yield response to water

Yield response to water

FAO IRRIGATION

ID DRAINAGE PAPER

33

byJ. DoorenbosWater Management SpecialistFAO Land and Water Development DivisionandA.H. KassamFAO ConsultantCrop ecologist - land-use planner withC.L.M. Bentvelsen,V. Branscheid,J.M.G.A. Plusje,M. Smith,G.O. Uittenbogaard and H.K. Van Der Wal

FOODAND

AGRICULTURE ORGANIZATION

OF THE UNITED NATIONS

Rome, 1906

Reprinted 1981, 1986, 1988

The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or o f its authorities, or concerning the delimitation of its frontiers or boundaries.

ISBN 92-5-100744-6

All rights reserved. No part o f this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, w ithout the prior permission of the copyright owner. Applications for such permission, w ith a statement of the purpose and extent of the reproduction, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy.

FAO 1979

- I l l -

To: C.E. Houston

The role which water plays in the production of agricultural crops is complex and the interacting processes involved in crop growth do not easily lend themselves to quantification. This draft publication ambitiously presents the relationship between water and crop yields in a simplified and easy-to-use form. Comments and suggestions for improvement of the presented methodologies and their practical application to the field, to be included in a.revised and possibly more complete edition, would be very welcome and should be forwarded to:

Chief, Water Resources, Development and Management Service

Land and Water Development DivisionFood and Agriculture Organization of the United Nations00100-Rome, Italy.

W ater is essentia l fo r crop production and best use o f availab le water must be made fo r e ffic ien t crop production and high y ield s . This requ ires a proper undet*- standing o f the e ffect o f water - ra in fa ll and/or irriga tion - on crop growth and yield under d ifferen t growing conditions.

A great deal has been published on aspects o f water relations in crop growth and attempts to understand crop response to water through crop growth modelling have met with success. H ow ever, fo r practica l application, a method is required to measure y ie ld response to water supply, which should be simple, requ ire commonly availab le clim atic, w ater, soil andcropdata, be w idely applicable with acceptable accuracy and allow easy verifica tion through adaptive research . With this in mind, the Land and W ater Development D ivis ion o f F AO initiated a study to establish generalized crop y ield and water use relationships o f twenty-six important irriga ted crops. An im pressive amount of related research information was generously made availab le by scientists contacted in the course o f the study (Appendix IV ) and was further obtained by a rev iew o f literatu re (Appendix 111). Valuable support was also rece ived from the International Institute for Land Reclamation and Improvement ( IL R l) , Wageningen, The N etherlands, in formulating the presented approach and through their co llection and analysis o f data and testing o f various water/crop y ield models. The resu lts o f the work by ILR I are herein further simplified and expanded in an effort to present results in an easy-to-use form.

This publication presents a methodology to quantify yield response to water through aggregate components which form the 'handles' to assess crop yields under both adequate and limited water supply. The method i s presented in Part A and takes into account maximum and actual crop y ie lds as influenced by water defic its using yield response functions relating re la tiv e y ield decrease and re la tive evapotranspiration de fic its . Part B gives an account o f w ater-re la ted crop yield and quality iriformation fo r twenty-six crops. Application o f the method provides the user with:

guidance in selection of irr iga ted crops under d ifferent growing conditions;

assessment o f crop yield under d ifferen t water supply regim es;

c r ite r ia , in terms o f crop production, on which to base p r io r it ies fur allocation o f limited water to crops both between and within p ro je c ts ;

d irec tives fo r fie ld water management for optimum crop production and water effic iency.

The publication lays down some o f the- important princip les involved in water management in relation to crop production. H ow ever, improvement for s ite-spec ific conditions w ill be needed with respect to the accuracy offered by the methodology and verification through adaptive research is required.

It should be pointed out that:

THE U PPE R L IM IT OF CROP PRODUCTION IS SET BY THE C LIM ATIC CON- D ITIONS AND THE GENETIC P O T E N T IA L OF THE CROP. THE EXTENT TO WHICH THIS L IM IT CAN BE REACHED W ILL A LW A YS DEPEND ON HOW F IN E LY THE ENGINEERING A S PE C T S OF W ATER SU PPLY ARE IN TUNE W ITH THE BIOLOGICAL NEEDS FOR W ATER IN CROP PRODUCTION. TH E REFORE, EFFIC IE N T USE OF W ATER IN CROP PRODUCTION CAN O NLY BE ATTA IN E D WHEN THE PLA N N IN G , DESIGN AND OPERATION OF THE WATER S U PP LY AND DISTRIBUTION S YSTE M IS GEARED TOWARD M EETING IN Q U AN TITY AND T IM E , INCLUDING THE PERIODS OF W ATER SHORTAGES, THE CROP W ATER NEEDS REQUIRED FOR O PTIM U M GROWTH Al^D HIGH Y IE LD S .

P R E F A C E

PagePA R T A : Y IELD AND W ATER 1

I . Maximum Y ield (Ym ) 3

II . Maximum Evapotranspiration (ETm ) 15

1. Reference evapotranspiration (E T o ) 17

2. Crop coefficien t (Re) 19

3. Maximum evapotranspiration (ETm ) 19

III. Actual Evapotranspiration (E T a ) 26

1. Adequate soil water 26

2. Limited soil water 27

IV . Actual Y ield (Y a ) 35

V . Y ield Response Factor (ky) 37

V I. Application in Planning, Design and Operation of.IrrigationPro jects 41

1. Adequate water supply 42

2. Limited water supply 48

3. Additional related applications 55

V II. Adaptive Research 58

1. S ite selection 59

2. 1 rrigation treatments 59

3. Experimental design 62

4. Data collection 63

5. Evaluation and presentation o f results 67

CONTENTS

v i l l

PART B: CROP AMD WATER

Pace

Alfalfa 69Banana 73Bean 77Cabbage 80Citrus 83Cotton 88

Grape 93

Groundnut 97Maize 101

O live 105Onion 109

Pea 112

Pepper 115Pineapple 118

Potato 121

Rice 125Safflower 131Sorghum 13d

Soybean 137

Sugarbeet U1

Sugarcane 145

Sunflower 150

Tobacco 153Tomato 157Watermelon 161

Wheat 164

APPENDIX 1 Calculation of Actual Evapotranspiration (E Ta) 171

APPENDIX 11 Glossary 173

APPENDIX III Persons and Institutes Consulted 177

APPENDIX IV Selected References l80

1 Good yields o f high-producing va rie ties adapted to the climatic ^conditions of the availab le growing season under adequate watersupply and high leve l o f agricultural inputs under irrigatedfarming conditions (ton/ha) ^

2 C lim atic, so il and water requirements for crops 6^73 Maximum active incoming shortwave radiation (Rse in cal/cm^/day)

and gross d ry matter production on overcast (yo ) and c lea r days (y c )(in kg/ha/day) fo r a standard crop 9

4 Correction for temperature (T ) 10

5 Production rates (ym in kg/ha/hour) fo r crop groups and meantemperatures 12

6 Correction for crop development over time and lea f area (c L ) I 37 Harvest index (cH ) o f high-producing va rie ties under irr iga tion (on

dry weight basis ) I38 Reference evapotranspiration (E T o in mm/day) for d ifferent agro-

climatic regions l 59 Saturation vapour pressure (ea ) in mbar as function o f mean a ir

temperature (T ) in °C 20

10 E x tra -te rres tr ia l radiation (R a ) expressed in equivalent evaporationin mm/day 20

11 Mean daily duration of maximum possib le sunshine hours (N ) ford ifferen t months and latitudes 21

12 E ffect of temperature f (T ) on longwave radiation (Rn l) 21

13 E ffect o f vapour pressure f(ed ) on longwave radiation (Rn l) 21

14 E ffect o f the ratio actual and maximum bright sunshine hours f(n/N)on longwave radiation (Rn l) 21

15 Values o f weighting factor (W ) fo r the e ffect of radiation on ETo atdifferent temperatures and altitudes 22

16 Adjustment factor (c ) in presented Penman equation 22

17 Pan coefficien t (kpan) for Class A pan for d ifferent groundcover andleve ls o f mean re la tive humidity and 24-hour windrun 24

18 Crop coefficien ts (kc ) 25

19 Crop groups according to soil water depletion 2820 Soil water depletion fraction (p ) fo r crop groups and maximum

evapotranspiration (ETm ) 28

21 Mean actual evapotranspiration (E T a ) in mm/day over the irriga tioninterval for d ifferent yields o f ETm (mm/day), D .S a (mm) and p (fraction ) 30-32

22 Monthly mean actual evapotranspiration (E Ta in mm/day) fo r A S l, remaining available soil water when ETa <ETm ( { ( l - p )S a .D j inmm/root depth) and maximum evapotranspiration (ETm in mm/day) 34

23 Sensitive growth periods for water defic it 36

24 Y ie ld response factor (ky) 3925 Relative total production (Pa/Pm ) for d ifferent values o f ETa/ETm

and ky factors for the total growing period 50

L IS T OF T A B L E S

PART A

YIELP AND WATER

The relationships encountered between crop, climate, water and soil are complex and many biological, physiological, physical and chemical processes are involved. A great deal of if-esearch information on these processes in relation to water is available; however, for practical application this knowledge must be reduced to a manageable number of major components to allow a meaningful analysis of crop response to water at the field level.

For application in planning, design and operation of irrigation schemes, it is possible to analyse the effect of water supply on crop yields. The relationship between crop yield and water supply can be determined when crop water requirements and crop water deficits, on the one hand, and maximum and actual crop yield on the other can be quantified. Water deficits in crops, and the resulting water stress on the plant, have an effect on crop evapotranspiration and crop yield. Water stress in the plant can be quantified by the rate of actual evapotranspiration (ETa) in relation to the rate of maximum evapotranspiration (ETm). When crop water requirements are fully met from available water supply then ETa = ETm; when water supply is insufficient, ETa < ETm. For most crops and climates ETm and ETa can be quantified.

When the full crop water requirements are not met, water deficit in the plant can develop to a point where crop growth and yield are affected. The manner in which water deficit affects crop growth and yield varies with the crop species and crop growth period. To evaluate the effect of plant water stress on yield decrease through the quantification of relative evapotranspiration (ETa/ETm), an analysis of research results shows that it is possible to determine relative yield losses if information is available on actual yield (Ya) in relation to maximum yield (Ym) under different water supply regimes. Where economic conditions do not restrict production and in a constraint-free environment, Ya = Ym when full water requirements are met; when full water requirements are not met by available water supply, Y a< Y m .

In order to quantify the effect of water stress it is necessary to derive the relationship between relative yield decrease and relative evapotranspiration deficit given by the empirically-derived yield response factor (ky), or:

/1 Y a \ 1 / 1 ETa \■ Ym ■ ETm^

where: Ya = actual harvested yield= maximum harvested yield

ky = yield response factorETa = actual evapotranspirationETm = maximum evapotranspiration

The value of ky for different crops is based on the evaluation of numerous research results, given in the bibliography, which cover a wide range of growing conditions. Extensive use has also been made of related known yield responses to soil salinity, depth of groundwater table and crop management practices. Based on experimental evidence, the relationship is given for the total growing period and the individual growth periods of the crops. Other than for different crops and crop growth periods, attempts to separate crop response to water according to climate, magnitude of maximum evapotranspiration and soil did not add to the accuracy obtainable.

Since the relationship is also affected by factors other than water, such as crop variety, fe r t i l izer , salinity, pests and diseases, and agronomic practices, the relationships presented re fer to high producing varieties, well-adapted to the growing environment, growing in large fields where optimum agronomic and irrigation practices, including adequate input supply, except for water, are provided.

With the presented relationships it is possible to plan, design and operate i r r i gation supply systems taking into account the effect of different water regimes on crop production.

CALCULATION PROCEDURE

I. Determine maximum yie ld CYm) o f adapted crop va rie ty , dictated by clim ate, assuming other growth factors (e .g . w ater, fe r t i l iz e r , pests and d iseases) are not lim iting.

II. Calculate maximum evapotranspiration (ETm ) when crop water requirements are fu lly met by available water supply.

III. Determine actual crop evapotranspi ration (E T a ) based on fa c to rs concerned with available water supply to the crop .

IV . Evaluate factors concerned with the interaction between w ater supply, crop water requirements and actual y ie ld (Y a ); through:

V . Selection o f y ie ld response factor (ky ) to evaluate re la tive y ield decrease as related to re la tive evapotranspiration d e fic it, o r (1 - Ya/Ym ) = k y ( l - ETa/ETm ), and obtain actual y ie ld (Y a ).

I. MAXIMUM YIELD (Ym)

The maximiim y ield le v e l o f a crop CYm) is prim arily determined by its genetic characteristics and how w ell the crop is adapted to the preva iling environinent. Environmental requirements o f clim ate, so il and water fo r optimum growth and yield vary with crop and crop va rie ty . A careful selection o f the crop and the va riety most suited to a given environment is o f paramount importance fo r obtaining high and effic ien t production.

Maximum yield o f a crop (Ym ) is defined as the harvested y ield o f a high- producing va r ie ty , well-adapted to the given growing environment, including the time available to reach maturity, under conditions where w ater, nutrients and pests and diseases do not limit y ie ld . Information on jrields indicates the maximum yields that are obtained under actual farming conditions, with a high le v e l o f crop and water management (Tab le 1).

Climatic factors which determine Ym are tem perature, radiation and length of the total growing season in addition to any specific temperature and daylength requ ire ments for crop development. In genera l, temperature determines the rate o f crop development and consequently affects the length o f the total growing period required fo r the crop to form y ie ld ; fo r example, a maize varie ty requ iring 100 days to reach maturity at a mean da ily temperature o f 25 to 30°C may take days at 20°C or 250 days or more at 15°C to reach maturity.

Some crops have specific temperature and/or daylength requirements for initiation o f certain growth and development; fo r example, fo r tuber initiation in potato night temperature o f below 15* C is normally requ ired ; in some sorghum varie ties flow ering is sensitive to short daylength, while in w inter wheat flowering requires both a cold period and long days. Furtherm ore, in some crops the quality o f yield is influenced by temperature; fo r example, in pineapple the sugar content of the fru it is determined by the temperature during y ie ld formation. A lso , many crops requ ire appropriate climatic conditions for yield formation, ripening and harvest.

Crop growth and y ield are affected by the total radiation received during the growing period . At a given radiation and temperature, crops d iffe r in their response to how much o f the total radiation received can be converted into growth and y ie ld . This d ifference has an important effect on how effic ien tly water can be utilized by the crop for production. Crop selection must therefore consider the radiation requirement and response o f crops in addition to temperature and daylength. For example, a good maize crop can convert 1 to 2 percent o f total radiation received into growth, whereas groundnut can convert half as much, although fo r a given location both crops may be suitable for production from the viewpoint o f other climatic requirements.

M ost crops o ffe r va rie ties which vary in their general and specific climatic requirements and in their length o f total growing period from sowing to harvest. This variation allows the crop to be adapted to a wide range o f climatic conditions and to the time period required and available for crop production. As an aid to crop selection , the length o f the total growing period , the temperature, daylength and other specific requirements are given (Tab le 2). Soil and nutritional requirements fo r each crop are also summarized in Table 2.

In addition to climatic requirements, the available growing season is also determined by the duration of an assured water supply of good quality. Consideration must be given to available water supply and crop water requirements, using a crop calendar in which demands for water are synchronized with the water supply available; fo r example, with the variation in r iv e r discharge and re s e rvo ir re lease . For some

crops the total growing period required fo r Ym must be manipulated by the leve l of water supply; fo r example, a reduction in water supply in the vegetative period of cotton hastens flow ering and boll formation, in addition to bringing the crop to maturity at the required time. For other crops, the growth required for Ym must also be manipulated by the le ve l of water supply during a particu lar growth period ; for example, in citrus a reduction m w ater supply w ill assist in checking excess vegetative growth and at the same time enhance flow er bud formation. The calculation o f total crop water requirements (FTm ) for maximum y ie ld (Ym ) is given in Chapter II and the leve l of water supply during the d ifferen t growth periods to regulate crop development and yield IS given fo r each crop in P a rt B. As an aid to crop selection in relation to total water required and maximum y ie ld , the water utilization e ffic iency (E y ) o r harvested yield per unit of water (kg/m^) and the sensitivity o f y ield to water de fic it are given (Tab le 2).

Other fa ctors , particu larly socio-econom ic, must also be considered in selection o f crops and length o f growing season, including, for example, farm ers' p re ference in relation to market demand, storage fac ilities and availab ility o f farmmachinery and labour.

Maximum yield (Ym ) can be calculated for d ifferen t climatic conditions. The methods enable quantification o f production potential o f d ifferent areas and thereby identify the most suitable areas fo r production fo r a given crop. The complexity of in terrelationships between many param eters makes the derivation of the methods complicated. However, their use is not, provided the essentia l data are availab le. Computation techniques are given for two selected methods:

1. An adaptation o f the method evaluated by the International Institute fo r Land Reclamation and Improvement ( IL R l),Wageningen, which is based on e a r lie r work by De W it,B ierhuizen, Rijtema, Feddes and Kowalik (see S labbers,1978).

2. The method developed by Kassam (1977) for the A gro - ecologica l Zone P ro je c t (see FAO W orld Soil Resources Report Z8, Report o f the A gro -eco log ica l Zone P ro jec t 1:A fr ic a , 1978).

1. THE 'W AGENINGEN' METHOD (a lfa lfa , m aize, sorghum, wheat)

Slabbers (1978) presents simplified water yield relationships which are c a librated and tested on extensive experimental data covering a wide T'ange o f climatic conditions. The so-called linear model is found to determine dry matter production adequately fo r a lfa lfa , maize, sorghum and wheat. Mathematical relationships are given to convert d ry matter production to yield o f marketable product depending on w ater shortages during d ifferent crop growth periods. A further simplification o f the linear model is given herein by assuming, amongst other assumptions, that maximum dry matter production occurs at maximum evapotranspiration, and by applying simplified corrections fo r d ry matter production to obtain marketable y ie ld . The possib le production potential fo r a given climate is calculated for a standard crop by the concept o f De Wit (1965), using radiation and evapotranspiration data; fo r application to agricultural crops corrections are required using crop-dependent constants and expressions o f the e ffect o f temperature, growth effic iency (resp ira tion ), and fo r the harvested part on final y ie ld . Since experimental fie ld data w ere used for calibration o f the method, the calculated 'experimental' y ield in dry weight (Ym e) must be adjusted to the yield leve l obtainable under actual farming conditions. H ow ever, Yme presen ts, fo r a given area, the re ference y ield leve l obtainable under a high standard oi crop and water management, where water and nutrients are not limited and pests and diseases are minimal.

Table 1 Good Y ields of High-producing Varieties adapted to the Climatic Conditions of the Available Growing Season under Adequate Water Supply and High Level o f Agricultural Inputs under Irrigated

Farming Conditions (ton/ha)

CROPClimatic Regions

T ropics V SubtroDics V Temperate y<20®Cy >200C <20°C >20oC <20«C >20°C

A lfa lfa hay 15 25 10

Banana fruit 40-60 30-40Bean; fresh pod 6-8 6-8 6-8

dry I grain 1 .5-2 ,5 1 .5-2 .5 1.5-2 .5Cabbage head 40-60 40-60 40-60

C itrus:grapefruit fruit 35-50 40-60lemon fruit 25-30 30-45orange fruit 20-35 25-40

Cotton seed cotton 3-4 3-4 .5

Grape fruit 5-10 15-30 15-25

Groundnut nut 3-4 3 .5 -4 .5 1-5-2M aize grain 7-9 6-8 9-10 7-9 4-6

O live fruit 7-10

Onion bulb 35-45 35-45 35-45

Pea : fresh pod 2-3 2-3 2-3dry grain 0 .6 -0 .8 0 .6 -0 .8 0 .6 -0 .8

Fresh pepper fruit 15-20 15-25 15-20

Pineapple fruit 75-90 65-75Potato tuber 15-20 25-35 30-40

Rice paddy 6-8 5-7 4-6

Safflower seed 2-4

Sorghum grain 3-4 3.5-5 3-4 3.5-5 2-3

Soybean grain 2.5-3-5 2 .5 -3 .5

Sugarbeet beet 40-60 35-55

Sugarcane cane 110-150 100-140

Sunflower seed 2 .5 -3 .5 2 .5-3 .5 2-2.5

Tobacco leaf 2-2.5 2-2.5 1.5-2

T omato fruit 45-65 55-75 45-65

Water melon fruit 25-35 25-35

Wheat grain 4-6 4-6 4-6

y Semi-arid and and areas only y Summer and winter rainfall areas y Oceanic and continental areas y Mean temperature

Table 2 C L I M A T I C . S OIL AND W A J E R RE QUI REMENTS FOR C ROPS

CropTotal growing

period(devsl

Temperature requirements for growTli",^C OD £ 1 m u/n an BC )

Daylength requirements for flowering

Specific climatic constraints/ requirements Soil requtrements

A lfalfa 100-365 24-26 (10-30) Day neutralSensitive to frost; cutting interval related to temp. ; requires low RH in warm climates

Deep, medium-tcstured, well- d ra in ^ , pH - 6 .5-7.5

Banana 300-365 25-30 (15-35) Day neutral

Sensitive io frost; temp. '*^8°C for longer periods causes serious damage; requires high RH, wind < 4 m/sec

Deep, well-dreined Loem without stagnant water; pH • 5-7

Bean fresh: 60-90 dry : 90-120 15-20 (10-27) Short day/

day neutralSensitive to frost; excessive ram, hot weather

Deep, friable soil, well-drained and aerated; opt. pH • 5 .5-6.0

Cabbage 100-150. 15-20 (10-24) Long day Short periods o f frost (-6 to -lO^C) are not harmful; opt. RH ■ 60-9C* Well-drained; opt. pH - 6 ,0-6.5

Citrvi* 240-365 23-30 (13-35) Day neutralSensitive to frost (dormant trees less), sirongwind, high humidity; cool winter or short dry period preferred

Deep, well-aerated, lighi to medium-textured oo ili, free from stagnant water; pH • 5-8

Cotton 150-180 20-30 (16-35) Short day/ day neutral

Sensitive to fro s t; strong or cold winds; temp. req. for boll development: 27-32“ C (18-38): d ry ripening period required

Deep, medium to heavy -texTuredsoils; pK • 5 .5-8.0 with opt. pH - 7,0-5.0

Grape 100-270 20 25 (15-30)

Resistant to frost during dormancy (down to '1 8 ^ 0 but sensitive during growth; long, warm to hot, dry summer and cool winter preferred/ reqoi red

WeLl-dretned , light soils are preferred

Groundnut 90- UO 22-28 (18-33) Day neutralSensitive to frost; for germination temp. >20“ C

Well-drained, friable, madium- (extured soil with loose top soil;pH - 5 . 5- 7 .0

Maize 100-140. 24-30 (15-35) Day neutral/ short day

Sensitive to frost; for germination temp. > 10®C: cool temp, causes problem for ripening

Well-drained and aerated soils with deep wetcr table and without waterlogging; opt. pH - 5-0-7.0

OUve 210-300 20-25(15-35)Scnsiuvc to frost (Jormant trees less); low winter temp, required (< 10°C) for flower bud initiation

Deep, well-drained soils free from wBtcrtcgging

Onion100-140

(.30-35 innursery)

15-20 (10-25) Long day/ day neutral

Tolerant to frost; low temp, ( < 14- 16*^C) required for flower initiation: no extreme temp, or excessive ram

Medium-textured soil; pH • 6.0-7-0

Pea fresh: 65-100 dry : 85-120 15-18 (10-23) Day neutral Slight frosi tolerance when young W ell -drained and aerated soils;

pH - 5- 5-6. 5

Pepper 120-150 16-23 ( I 5- 2?) S hort day/ day neutral Sensitive to frost Light to medium-textured soils;

pH - 5 .5-7-0 _

Pineapple 365 22-26 (18-30) Short day Sensitive to frost; requires high RH; queliiy affected by temperature

Sandy loam with low line content; pH • 4-5-6.5

Potato 100-150 15-20 (10-25)Long day/ day neutral

Sensitive to frost; night temp.< l7*C required for good tuber initiation

Well.drained , aerated and porous soils; pH ■ 5-6

Rice 90-150 22-30 (18-35) Short day/ day neutral

Sensitive to frost; cool temp, causes head sterility; small difference in day and night temp, is preferred

Hesvy soils preferred for p ercolation losses, high tolerance to O2 deficit; pH * 5. 5-6-0

Safflower spring: 120- 160 autumn; 200-230

early growth:15-20

later growth :_ 20-30 (10-35)

Tolerant to frost; cool temp. req. for good establishment and early growth

Fairly deep, well-drained soils, preferably medium-textured;pH - 6-8

Sorghum 100-140. 24-30 (15-35) Short day/ day neutral

Sensitive to frost; for germination temp.> lO^C ; cool temp, causes head sterility

Light to medium/heavy eotls relatively tolerant to periodic waterlogging, pH - 6-8

Soybean IOO-I3O 20-25 (10-30) Short day/ day neutral

Sensitive to frost; for some var- temp. >24®C required for flowering

Mhde range of soil except sandy, well-drained; pH - 6-6.5

Sugerbeet 160-200 18-22 (10-30) Long dayTolerant to light frost; toward harvest mean daily temp. <10®C for high sugar yield

Medium to slightly heavy- texturm) soils, friable and well- drained; pH “ 6-7

Sugarcane 270-365 22-30 (15-35)Short day/ day neutral

Sensitive to frost; during ripening cool (10-20®C), dry, sunny weather is required

Deep, well aerated with ground water deeper than 1. S-2 m but rc l. tolerant to periodic high watertables and On deficit; pH - 5- 8-5; opt pH - 6,5

Sunflower '90-130 10-25(15-30) Short day/ day neutral

Sensitive to frost Fairly deep soils; pH - 6-7-5

Tobacco90-120

( . 40-60 in nursery

20-30(15-35)Short day/ day neutral

Sensitive to frost Quality of leaf dnends on soil texture; pH * 5-6-5

Tomato90-140

(.25-35 innuriervJ

18-25 (15-28) Day neutral Sensitive to frost, high RH, strong wind; opt, night temp. 10-20^C

Light loam, well-drained without waterlogging; pH • 5-7

Water melon 80-110 22-30 (18-35) Day neutral Sensitive to frost Sandy loam is preferred; pH *5-18-7.2

Wheel Spring: 100-130 winter: l80-250

15-20 ( 10-25) Day neutral/ long day

Spring wheat t sensitive to frost; Winter wheat ; resistant to frostduring dormancy C > - l8®C), sensitive during post-dormancy period; requires a cold period for flowering during early growth. For both, dry period required for ripening

Medium-tcxture is preferred; relatively tolerant to high water table; pH ■ 6-8

V mean daily tamperaturas y ky of tbe total growing p e r i^ ;

medtum' Lowmeditim.hiahhigh

ky < 0.85 ky 0.85 - 1.0 ky l.O - 1.15 ky >1.15

Sensittvity to ftal mity

F e r t iliz e r requirements N : P 1 K

Itg/ha/growing period

W aterrequirement s

mm/growing Deriod

Sensitiv ity to water supply

Ckv)3'

W ater utilization e ffic iency for happened y ie ld , Ey, kg/m3

(H moisrurc)

Crop

moderatelysensitive O-iO : 53-65 : 75-100 800-1600

low tomedium -high (0 .7 -1 .1 )

I . 5 - 2.0

hay (10 -15%)A lfa lfa

sensitive 200-A00: Z5-bO : 1200-2200high(1 .2 -1 .3 5 )

plant crop ; 2. 5-4 ratoon : 3-5*6

fruit (70%)

Banana

sensitive 20-ZD : iO -60 : 50-120 300-500 medium-high(1 . 15)

lush : 1-5-2 .0 (80-90% ) d ry : 0 . 3 -0.6 ( 10%) Bean

moderatelysensitive 100-150; 50-65 : 100-UO 380-500 medium-low

(0 .9 5 )12-20

head (90-95%) Cabbage

sensitive 100-200; 35-45 : 5 0 -I60 900-12001 ow to medium -high (0 .3 - 1 . 1 )

2-5

fruit (85%, lime: 70%) Citrus

tolerant 100- 180; 20-60 : 50-60 700-1300 medium-low(0 .8 5 )

0 .4 -0 .6 seed cotton ( 10%) Cotton

moderatelysensitive 100-160: 40-60 : 160-230 500-1200 medium - low

(0 .85 )

2-4

fresh fruit (80%)Grape

moderatelysensitive 10-20 : 15-40 : 25-40 500-700 low

(0 .7 )

0 . 6-0.8 unshelled d ry nut ( 15%) Groundnut

moderately sensiti ve 100- 200; 50-80 : 60-100 500-800 high

(1 .25 )0 . 8- 1.6

gram ( 10- 13%)M aize

moderatelytolerant 200-250; 55-70 : l60-210 600-800 low

1 . 5- 2.0 fresh fruit (30%) O live

sensitive 60- 100: 25-45 ; 45-80 350-530 medium-hi gh(1 .1 )

8-10

bulb (85-90%) Onion

sen sitive 20-40 : 40-60 : 8O -I6O 350-500 medium-highD .1 5 )

fresh ; C-5-0-7shelled (70-80%)

d rv : 0 .15 -0 .2 (12%)Pea

moderately sen sitive lo o - 170: 25-50 : 5O-IOO 6tK)-900

(1250)

medium-high(1 ,1 )

1 .5- 3.0fresh fruit (90%) Pepper

230-300: 45-65 : 110-220 700-1000 lowplant c ro p : 3-10 ratoon ; 8-12 fruit (85%)

Pineapple

moderatelysensitive 80-120: 50-60 : 125-160 500-700 medium - high

(1 .1 )4-7

fresh tuber (70-75%)Potato

moderatelysensitive 100-150: 20-40 i 80-120 350-700 hign

0 . 7 - 1 .1paddy (15 20%) Rice

moderatelytolerant 60-110: 15-30 : 25-40 600-1200 low

(0 .8 )0 .2 -0 .3

seed (8-10%) Safflow er

moderatelytolerant 100- 180: 20-45 : 35*80 450-650 medium - low

(0 .9 )

0 .6 -1 .0

grain (12-15%) Sorghum

moderatelytolerant 10-20 : 13-30 : 25-60 450-700 medium - low

(0 .8 5 )0 .4 -0 .7

gram (6-10%) Soybean

tolerant 150 : 50-70 : 100-160 550-750low to medium-low (0 .7 - 1 . I )

beet ; 6-9 (80-85%) sugar; 0 .9 -1 .4 ((7%) Sugarbeei

moderatelysensitive 100-200; 20-90 : 125-160 1500-2500 high

(1 .2 )

cane : 5-8 (80%)

sugar; 0 .6 -1 .0 (0% ) Sugarcane

moderately t olerant 50- 100 : 20-45 ; 60-125 600-1000 medium-low

(0-95 )0 .3 -0 .5

seed (6-10%) Sunflower

sensitive 40-80 : 30-90 : 50-110 600-600 medium - low(0 .9 )

0 .4 -0 -6 cured leaves (3-10%) Tobacco

moderatelysensitive 100-150: 65-110 ; 160-240 400-600 medium -high

(1 .0 5 )10-12

fresh fruit (80-9(7%) Tomato

moderatelysensitive 80-100: 25-60 : 35-80 400-600 medium-high

( l . l )5-a

fruit (90%) W ater melon

moderatelytolerant 100-150: 35-45 ; 25-50 450-6-X)

medium-htgh ( spring: 1. 15 w inter: 1.0)

0 .6 -1 .0

a r a 1 - M J - 1 5%' Wbcat

1 kg P - 2.L kg P jO -

I kg K - ] . 2 kg K 2O

C A L C I M A T I O V P P O C ^ n V R F

To calculate ‘experimental' yield (Yme) the step* needed are:

a. Calculate gross dry matter production of * standard crop CYo),

b. Apply correction for climate (ETm /(ea-ed ))*

Apply correction for crop species (K ).

Apply correction for temperature (cT ) .

Apply correction for harvested part (cH)*

a. Calculation of Gross Dry Matter Production o f Standard Crop (Yo )

To calculate Yo m kg/ha/day for a g i v en l o c a t i o n , the method of De Wit (1965) is used. This method is based on the leve l of incoming active shortwave radiation forsl/ird ar'? cond it lor :

Yo - . ' W U ’C

w (iC ro

Yo - gross dry matter production of a standard crop, kg/ha/dayF - fraction of the da^ime the sky is clouded, fraction; or

F • (Rse - 0.5Rs)/0.8Rsc where Rse is the maximum active incoming shortwave radiation on clear days in cal/cm^/day (Table 3) and Rs is the actual measured incoming shortwave radiation in cal/cm^/day V

VO - gross dry matter production rate of a standard crop for agiven location on a completely overcast day, kg/ha/day (Table 3)<ross dry matter production rate of a standard crop for a given location on a clear (cloudless) day, kg/ha/day (Table 3)

orrection for Effect o f Climate (ETm/(ea-ed))

In addition to radiation, the rate of crop growth for a given climate is closely related to the ratio mean maximum evapotranspiration (ETm) in mm/day and the vapour pressure dehcit (ea-ed ) in mean daily mbar over the total growing period (Bierhuizen and SU tyer , 1965)* f Calculation of ETm is given in Chapter II; for calculation of, mean saturation vapour pressure (ea ) and mean actual vapour p r e s s u r e both in mber (Table 9)» see Chepter II, 1 .1 Penman Method.

Rs IS also expressed in mmMay equivalent evaporation; conversion is 59 cal/cm? I mm equivalent evaporerton. When only sunshine duration data are available, Rs can also be calculated from Rs - (0.25 ♦ 0. 50 n/N)Ra, where Ra is the extra- tarrastnal radiation m mm/day (Table 10), N is the maximum possible sunshine duratioo in hours/day (Table 11) and n is the actual measured sunshine duration in hours/day*When expressed in mm Hg conversions , I mbar - 0. 75 mm Hg.

Table 3 Maximum A c t ive Incoming Shortwave Radiation (R se in cal/cm^/day) and Gross Dry M atter Production on O vercast (yo ) and C lear Days (y c ) (in kg/ha/day) fo r

a Standard Crop (De W it , 1965)

North

South

Jan

July

Feb

Aug

M ar

Sept

Apr

Oct

M ay

Nov

June

Dec

July

Jan

Aug

Feb

Sept

M a r

Oct

Apr

Nov

May

Dec

June

0° Rse 3/ 3 360 369 364 349 • 337 343 357 368 365 349 337yc A13 U2L 429 426 417 410 4 13 422 429 427 418 410yo 219 226 230 228 221 216 218 225 230 228 222 216

10° Rse 299 332 359 375 377 374 375 377 369 345 3 1 1 291yc 376 401 422 437 440 440 440 439 431 411 385 370yo 197 212 225 234 236 235 236 235 230 218 203 193

20° Rse Z49 293 337 375 394 400 399 386 357 313 264 238yc 332; 371 407 439 460 468 465 451 425 387 348 325yo 170 193 2 15 235 246 250 249 242 226 203 178 164 •

30° Rse 191 245 303 363 400* 417* 411* 384* 333 270 210 179yc 281 333 385 437 471* 489* 483* 456* 412 356 299 269yo 137 168 200 232 2 5 1 * 261* 258* 243* 216 182 148 130

dO° Rse 131 190 260 339 396 422 413 369 298 220 15 1 118yc 219 283 353 427 480 506 497 455 390 314 241 204yo 99 137 178 223 253 268 263 239 200 155 112 91

* Values used in calculation example

10

C* Correction for Crop Species CK)

To relate gross dry matter production of a standard crop (Yo ) to gross dry matter production of alfalfa, maize, sorghum and iwheat (Yo . ETm/ca-ed)), empirically- derived crop constants (X ) are used with a value for alfalfa eaual 0 .9 , for maize equal 1 . 9 , for sorghum equal 1.6, for spring wheat equal 1-17 and for winter wheat equal 0.65<

d. Correction for Temperature (cT )

The production of a standard crop (Yo) is presented for standard temperature conditions. For actual mean daily temperature during the total growing period, a crop- spccific temperature correction (cT ) is applied to obtain net dry matter production (Ydm) taking into account the ^0 percent of total energy required by the plant for growth and maintenance processes (respiration). For a crop with optimum plant density, Ydm - K. cT . G . Yo . ETm/(ea-ed) in kg/ha/penod, where Yo is taken as the average over a total growing penod of G days.

Table L Correction for Temperature (cT )

Mean temperature over the total growing period, °C5 10 15 20 25 30 35

Alfalfa 0 0.2 0.55 0,6 0.6 0,5Maize 0 0. 1 0.35 0.5 0.6* 0 . 6* 0.6Sorghum 0 O.l 0.3 O .iS 0.55 0.6 0.6Wheat 0.05 0.3 0.55 0.6 0.35 0 . 1 0

« . Correction for Harvested Part (cH)

In general, only a part of the total dry matter is harvested. For alfalfa about 50 percent of the net total dry matter is formed in the roots during the first year of growth and about 10 percent for the subsequent years. When maize, sorghum and wheat are grown for gram, only a fraction of the total dry matter is Harvested, The ratio between net total dry matter and harvested yield is given by the harvest index (cH) for high-producing varieties under irrigation;

Alfalfa

MaizeSorghumWheat

cHO.A • 0 , j0.8 - 0.9 0 .^ - 0.5

0.35 - 0.^50 1 '

I 1 r y C A T

subsequent years

In summary, tl'O production (Yme) under experimental conditions of a h i g h -

producing, climaticallv adapted variety, grown under optimum climatic conditions is

" ~ ■■ ’ ■ - ETm/(e«-ed) kg/h«/perio<l|Tm /{e .- .d ) k g / h a / p e n o d

ETm/(ea.ed) kg/ha/penod ETm/(ca-ed) kg/ha/penod FTm/(ea-ed) kg/ha/penod

AUalfa YmeMaize YmeSorghum YmeSpring wheat YmeWinter wheat Yme

0.9 .cH 1.9 . cH1.6 .cH 1 . 1 7 . cH 0 .65 . cH

cTcTcTcTcT

GGGGG

YoYoYoYoY o

I ]

EXAMPLE

Given: Maize, with optimum plant density; location 3 0 ^ ; attitude 95m;total growing period 1/3 days from 1 May to 31 August; mean incoming shortwave radiation (Rs) over the total growing period 65O cal/cm^/day; mean temperature 27-5°C; mean relative humidity 55^: mean maximume v a p o t r a n s p i r a t i o n ( E T m ) is 6 , 8 m m /d a v : I i r \ mHex ( c H ) i s 0 *4 S.

Calculation:

yoyoRseFYoETmeaedea-edcTYme

meanmeanmeanmeanmeanmeanmeanmeanmeanfractiontotalperiod

(A03 - 0.5 X 650)/(0.8 X i03) (0.2A X 253) ♦ (1 - 0.2A)ii75

at 27.5°C ea X RH/100

at 27.5°C

1 .9 x 0 . i5 x 0 .6 x 123x^22b .o/ 16.6

Table 3 253 kg/ha/dayTable 3 475 kg/ha/dayTable 3 403 cal/cm^ /daycalc 0.24calc 422 kg/ha/dayChap. 2 6.8 mm/dayTable 9 36.8 mbarcalc 20.2 mbarcalc 16.6 mbarTable L 0.6ale 10910 kg/ha

grain dry weight

2, THE AGRO-ECOLOGICAL ZONE METHOD

The methodology to calculate crop production was developed to sun the assessment on a continental basis. However, the method can also be applied to a degree of detail required to suit specific locations. For a given climate, the possible potential yield is calculated for a standard crop using the concept of De Wit (1965) using radiation data; for agricultural crops, corrections are made for the genetically-controlled growth processes of the crop under the given climate. It is assumed that the climatic requirements of the crop are met and that water, nutrients, salinity, pests and diseases do not affect crop growth and potential yield (Ymp).

Under actual farming conditions, vield losses will occur due to adverse climatic conditions over short periods, limited water and nutrient supply, and problematic farm operations including land preparation, weeding and harvesting. These constraints are complex and it is difficult to quantify their effect on yield. However, when compared to actual farmers' yields, the calcu late potential yield (Ymp) will give an indication of the efficiency in agricultural production.


To calculate potential yield (Ymp) the steps needed are:

a. Calculate gross dry matter production of a standard crop (Yo)«b. Apply correction for crop species and temperature.c. Apply correction for crop development over time and leaf area (cL)«d. Apply correction for net dry matter production (cN).e. Apply correction for harvested parr r. H).

12

A. Calculation of Gross Dry Matter Production of a Standard Crop CVo)

As in Yo in ka/ha/day is calculated for a given location applying the concept of De Wu (1965):

where:Yo - F -

yo

yc

Yo “ F . yo + ( l - F )y c

?[ross dry matter production of a standard crop, kg/ha/day raction of tlie daytime the sky is clouded, fraction; or

F • (Rse - 0.5Fs)/ O.BRse where Rse is the maximum active incoming shortwave radiation on clear days in cal/cm^/day (Tab le 3) and Rs is the actual measured incoming shortwave radiation in cal/cm?/day. Rs can also be calculated from measured sunshine duration data (n) in hours/day gross dry matter production rate of a standard crop for a given location on a completely overcast day, kg/ha/day (Table 3)gross dry matter production rate of a standard crop for a given location on a clear (cloudless' day, kg/ha/day (Table 3)

b. Correction for Crop Species and Temperature

The gross dry matter production is crop species and temperature dependent, production rate (ym) can be la rger or smaller than 20 kg/ha/hour as assumed for the standard crop. Production rales (ym) in kg/ha/hour for groups of crops are given ii Table 5*

The

Table 5 Production Rates (ym in kg/ha/hour) for Crop Groupsand Mean Temperatures

Cropgroup 5 10

Mean temperature,15 20 25 30 35 40 45

1 cool 5 15 20 20 15 5 0 0 0I warm ') 0 15 32.5 35 35 32.5 5 0II cool i' 3 •iS 65 65 65 45 5 011 warm 0 0 5 ^5 65 65 65* 45 5

I cool:I warm

II cool: It warm

alfalfa, bean, cabbage, pea, potato, tomato, sugarbeel, wheal alfalfa, citrus, cotton, groundnut, pepper, rice, safflower, soybean, sunflower, tobacco, tomato some maize and sorghum varieties maize, sorghum, sugarcane

Applying Oe Wit's concept, the value of yo and yc can be adjusted for different crop groups:

1 «hcn ym >20 kg/h«/hour' o - FCO.fl ♦ 0.01 ym)yo ♦ (1 - FVO. > 0 .02" v-mVc kg^ha/day.henrm <20 kg/ka/hour

' ‘'-025 ynt)yo ♦ U “ i Xu. kg; ha day

c. Correction for Crop Development over Time and Lea f Area (c L )

In relation to the maximum growth rate during the middle of the total growing period, crop growth will be small at the start and the end of the growing penod or the average rate over the growing period is about 50 percent o f the rate during the maximum growth. A lso for the standard crop an active leaf area o f five times the ground surface IS assumed (LA I • 5)* When leaf area is smaller a correction must be applied; whengreater than 5 the effect is small (Table 6).

Table 6 Correction for Crop Development over Timeand Leaf Area u L )

13

LAI 1 2 3 4 >5

Correction cL 0.2 0.3 0.48 0.5*

d. Correction for Net Dry Matter Production (cN )

To maintain dry matter production, e n e r ^ is required by the plant for the within- plant growth processes (also called respiration). Only the remaining energy can be used to produce new growth which is about 0.6 for cool (mean temp. < 20<>C) and 0 .5 for warm (mean temp. >20°C) conditions, or cN - 0 .5 to O.b,

e. Correction for Harvested Part (cH)

In general, only a part of the total dry matter such as gram, sugar or oil is harvested. The ratio between net total dry matter and harvested yield is given by the harvest index (cH) for high-producing varieties under irrigation (Table 7).

Table 7 Harvest Index (cH ) of High-producing Varietiesunder Irrigation (on Dry Weight Basis)

Crop Product cH Crop Product cH

Alfalfa hay 0 .4 -0 .5V Potato tuber 0.55-0.650.8-0.9V Rice grain 0 .4 -0 ,5

Bean gram 0.25-0.35 Sorghum gram 0.3-0 .4Cabbage head 0 .6 -0 .7 Soybean grain 0 .3 -0 .4Cotton lint 0 . 08-0 .12 Sugarbeet sugar 0.35-0.45Groundnut gram 0.25-0.35 Sugarcane sugar 0 .2 -0 .3Mai ze grain 0.35-0.45* Sunflower seed 0 ,2 -0 .3Onion bulb 0,7 -0 .8 Tobacco leaf 0 .5 -0 .6Pea grain 0.3 -0 .4 Tomato fruit 0.25-0.35Pepper fruit 0 .2 -0 .4 Wheat gram 0.35-0.45Pineapple fruit 0 .5 -0 .6

V first and second year

M

a .

In summary, potential yietd (Ymp) o f a high-producing, climaticaUy adapted Rrown under constramt-free conditions over a gi^oving period of G days is:

whenym >20 kg/Ka/hourYmp - . cN , cH . G [ F(0.8 ♦ 0,01 ym)yo ♦ (1 -FXO, 5 + 0.025ym)vc ]

kg/ha/period

b. when ym <20 kg/ha/hourYmp • cL . cN . cH . G [F(0»5 + 0.025ym)yo + (l-FX0.05yn')y<^]

kg/ha/penod

wherecL - cN -

cH - G - F . ym -

yo •

yc .

correction crop development and leaf area (Table 6) correction for dry matter production, 0.6 for cool and 0.5 for warm conditionscorrection for harvest index (Table 7)total growing period (days)fraction of the daytime the sky is cloudedmaximum leaf gross dry matter production rate of a crop for a given climate, kg/ha/day (Table 5)gross dry matter production of a standard crop for a given location on a completely overcast (clouded) day, kg/ha/day (Table 3) gross dry matter production rate of a standard crop for a given location on a clear (cloudless) day, kg/ha/day (Table 3)

EXAMPLEGiven : Maize; location 3 0 ^ ; total g r o w i n g period ( G ) 1 2 3 days f r o m1 May to 31 August; LAI is 5; average incoming shortwave radiation (Rs) over growing period 650 cal/cmVday; average mean temperature 27-5®C.

Calculation:

yoy<RseFym cL cH cNGYmp

mean Table 3 253 kg/ha/daymean Table 3 475 kg/ha/daymean Table 3 403 cal/cm^daymean 403 - 0.5 X 650/0.0 X 403 calc 0.24

at 35°C Table 5 65 kg/ha/hat LAI - 5 Table 6 0.5

Table 7 0.4at 27.90C given 0.5

given 1230 .5x0 ,5?t0 .4x 123 [0.24(0.8 + 0.01

x 65)253 ♦ (1-0.24X0.5 + 0.025x65X75] calc 10520 kg/ha

NBi Th« derived yield using the two methods to calculate the ’experimental’ (Yme) and ^^ ten tia l ’ yield (Ymp) would seem high in relation to actual field production. However, for the location in question (Gira. UAR), the measured gram yield of maize with irnga - tton at 50 percent depletion of available toil “ "o »>th measured crop water use of6 850 10. J ton/ha (El Maghraby, 1969).

11. MAXIMUM EVAPOTRANSPIRATION (E T a )

CUmaic IS one of the niosv imporioM factors determining the crop water requ ire ments needed for unrestricted optimum growth and y ie ld . Crop water requirements are normally expressed by the rate o f evapotranspiration (E T ) in mm/day or mm/period.The leve l o f ET has been shown to be related to the evaporative demand of the a ir . The evaporative demand can be expressed as the re ference evapotranspiration (E T o ) which, when calculated, predicts the effect of climate on the level of crop evapotranspiration; ETo represents the rate of evapotranspiration of an extended surface o f an 8 to I 5 cm tall green grass co ve r , actively growing, completely shading the ground and not short o f water. Methods to calculate ETo are given, i . e . the Penman, Radiation and Pan Evaporation Methods, Approximate values for ETo in mm/day for different agro- climatic regions are given in Table 8.

Empirically-determined crop coeffic ients (Vc) con be used to re late ETo to maximum crop evapotranspiration (ETm) when water supply fully meets the water requirements of the crop. The value of kc va n es with crop, development stage of the crop , and to some extent with wmdspeed and humidity. For most crops , the kc value increases from a low value at time of crop emergence to a maximum value during the period when the crop reaches full development, and declines as the crop matures.Values of kc fo r different crops are given m Table 18 and in Part B,

For a given climate, crop and crop development stage, the maximum evapotranspiration (ETnO in mm/day o f the period considered is :

ETm - kc . ETo

Maximum evapotranspiration (ETm) re fe rs to conditions when water is adequate for unrestricted growth and development; ETm represents the rate of maximum evapotranspiration of a healthy crop, grown in large fields under optimum agronomic and irrigation management.

The methods presented allow prediction of ETm within 10 to 20 percent accuracy provided the meteorological data are re liab le and obtained from a representative a g r i cultural environment, and provided total growing period and lengths of development stages are known. For details see Doorenbos and Pruitt (1977).

M eteoro logica l data used in the calculation of ETm should pre ferab ly be collected at stations situated within an agricultural ( irr iga ted ) area. When data are collected at stations in d ry , bare a reas , at a irports or even on rooftops, the calculated ETm values should be corrected since the data do not represent the different micro-chmates found within the irr igation schemes. In and and sem i-and areas with moderate wind, ETm calculated with data obtained outside the irr igated area may need to be adjusted downward by 20 to 25 percent.

C A LC V LAT IO N PROCEDURE

1, Reference Evapotranspiration (F T o )Collect and evaluate available meteorological and crop data; based on ineteorological data available, select method of calculation. Compute ETo in mm/dayfor each 30 or 10-day period using mean meteorological data.

2, Crop Coefficient (kc)Determine growing period and length of crop development stages and select kc values.

16

Tabic 8 Reference Evapotranspiration (ETo m mm/day) forDifferent Agro-clim atic Regions

R.gion . ^,0Mean daily temperature,

. _ __2£oc

,>30(cool) (moderate)

t(warm)

TROPICShumid 3 - L 4 - 5 5 - 6subhum id 3 - 5 5 - 6 7 - 8semt-and d - 5 6 - 7 8 - 9and L - 5 7 - 8 9 - 10

SUBTROPICS

Summer rain fall;humid 3 - 4 4 - 5 5 - 6subhumid 3 - 5 5 - 6 6 - 7

semi-and ^ - 5 6 - 7 7 - 8and 4 - 5 7 - 8 1 0 -1 1

Winter rainfall

humid - subhumid 2 - 3 4 - 5 5 - 6semi-arid 3 - 4 5 - 6 7 - 8and 3 - 4 6 - 7 10 -11

TEMPERATEhumid - subhumid 2 - 3 3 - 4 5 - 7semi-and - arid 3 - 4 5 - 6 8 - 9

1 7

3. Maximum Evapotranspiration (ETm )Calculate HTm in mm/day for each 30 o r 10-day penod from ETm - kc I f needed, adjust ETm accord ing to data source.

ETo.

1. R h rE R b N C E E V A P O T R A N S P IR A T IO N (E T o )

1.1 Penman Method

Climatic data required a r e : mean temperature (T m ®C), mean re la t ive humidity (RH in %), total windrun (I) m km/day at 2 m height) and mean actual sunshine duration (n in hour/day) o r mean radiation (Rs o r Rn equivalent evaporation in mm/day). A lso measured o r estimated data on mean maximum re la t iv e humidity (RHmax in %) and mean daytime windspced (Uday in m/sec at 2 m height) must be ava ilab le . R e ference evap o transpiration (E T o ) representing the mean value in mm/day, o v e r the period considered , IS obtained b y :

w here :

(ea -ed )

f(U )

Rn

Wc

ETo W. Rn ♦ (1 -W ) . fCU). (e a -e d ) )

vapour p ressu re de fic it i . e . the d if fe rence between saturation vapour pressu re (ea ) at Tmean in mbar (Tab le 9) and actual vapour p ressu re (cd ) in mbar where ed - ea - RH/ICX) wind function o f fCU) * 0 .27 (1 + U/100) with U in km/day measured at 2 m heighttotal net radiation in mm/day o r Rn ■ 0*75Rs - Rnl where Rs is mcommg shortwave radiation in mm/day either measured o r obtained from Rs - (0 .25 + 0 .50 rVN)Ra. Ra is e x tra - te r r e s t r ia l radiation in mm/day (Tab le 10), n is the mean actual sunshine duration in hour/day and N is maximum possib le sunshine duration in hour/day (Tab le 11). Rnl is net longwave radiation in mm/day and IS a function of temperature. f (T ) , o f actual vapour p ressu re , f (ed ) and sunshine duration , f(n/N), o r Rnl • f (T ) , f (n/NV f(ed ) (Tab les 12, 13 and U )temperature and altitude dependent weighting factor (Tab le 15) adjustment factor fo r ratio Uday/Unight, for RHmax and fo r Rs (Tab le 16)

E X A M P L E

G iven : Location 3 0 ^ ; altitude 95 ; July; Tmean 28, 5®C; RHmean 55*:Umean 232 km/day; n mean 11. 5 hour/day; (RHmax 80%, Uday 3 m/sec,Uday/b'night 1.5).

Calcu la tion :

ea T - 28,5®C Table 9ed e a . RH/100 calcea-ed calcfCU) 0.27(1 + U/lOO): U - 232 km/day calcRa , July T a b u 10N 30<^N , Julv Table 11Rs (0 .25 ♦ 0 .50n/N )R a 1 calcRnl f ( T ) . f (e d ) . f(n/N) Tables 12, 13, 14Rn 0.75RS - Rnl calcW T - 28.5®C; 95 m Table 15c RHmax 80%; Rs 11. 2; Uday/Unight 1.5 Tab le 16ETo c 1 W . Rn ♦ (1 -W ) . K V ) . (ea -ed ) l rs lr

38.9 21.41 2 ^

.e13.9 11.2

1.8

M

mbarmbarmbar

mm/day hour/day mm/day mm/day

/<Uy

mm n

18

1. 2 Radiation Method

Climatic data reouired are mean temperature (T m °C ) and mean actual sunshine duration (n in hour/day) or mean incoming shortwave radiation (Rs in mm/day equivalent evaporation). Estimated values of mean re lative humidity (RH in %) and mean daytime windspeed (Uday in m/sec at 2 m height) muft be available.

overReference evapotranspiration CETo in mm/day) representing the mean daily value

the period considered is obtained by:

where: Rs -

Wc

by :

ETo - c (W . Rs)

measured mean incoming shortwave radiation in mm/day o r is obtained from Rs - (0.25 + 0 .50n/N)Ra where Ra is extraterrestr ia l radiation in mm/day (Table 10), N is maximum possible sunshine duration in hour/day (Table 11) and n is measured mean actual sunshine duration m hour/day temperature and altitude dependent weighting factor (Table 15) adjustment factor made graphically on W . Rs using estimated values of RHmean and Udaytime (F igure 1).

EXAM PLE

Given: Location 3 0 ^ ; altitude 95 nt; July; Tmean 28.5*^C; n11.5 hour/day; Uday mean - moderate (2 to 5 m/sec); RHmean • (about 55X).

Calculation:

meanmedium

Ra 3 0 ^ ; July Table 10 16.8 mm/dayN 3 0 ^ ; July Table 11 13.9 mm/dayRs (0,25 ♦ 0 .50n/N )Ra calc 11.2 mm/dayW T - 20.5°C; 95 m Table 15W . Rs calc mm/dayETo RH 55%; U - 2 to 5 m/sec Fig. 1 8.4 mm/day

1.3 Pan Evaporation Method

Data required are mean pan evaporation (Epan in mm/day), estimated values of mean relative humidity (RH in %) and mean wmdrun (U in km/day at2 m height) and information on whether the pan is surrounded by a cropped or dry fallow area.

Reference evapotranspiration (E T o ) representing the mean value in mm/day over the period considered is obtained by:by

ETo k pan . Epan

where:

Epan - evaporation in mm/day from an unscreened class A evaporation pan k pan - pan coefficient (Table 17)

tX A M P L L

Given: July; E class A pan 11.3 mm/day; RHmean • medium; Umean okoderatc; pan surrounded by cropped area of several hectares.

19

Calculation:kpan RH - medium; U - moderate; cropped Table 17 0.75ETo kpan.Epan calc 0^^ min/day

2 CROP COEFFICIENT (kc)

Information required on crops is :

the date of sowingthe length of the total growing season, includingthe duration of initial stage (germination to 10 percent ground cover) the duration of crop devel^ment stage (from 10 percent to QO percent ground cover)the duration of the mid-season stage (from 80 percent ground cover to start of ripening)the duration of late season stage (from start of ripening to harvest).

General information on crop development stages vs given for different crops in Part B. For crop coefficients see Table 18. Climatic data required for the selection of kc values are wmdspeed and humidity.

The value of the crop coefficient (kc) vanes with the development stages of the crop. For most crops the kc value for the total growing period is between 0.85 and 0.9 with the exception of a higher value for banana, rice, coffee and cocoa and a lower value for citrus, grape, sisal and pineapple.

EXAMPLEGiven: Maize; planted 1 May; harvested 31 August; initial stage is 20 days; development stage 35 days; mid-season stage 40 days; late season stage 28 days; wmdspeed is light to moderate; minimum mean relative humidity is low.

Calculation: From Part B, Maize, or from Table 18:

kc May • 0.4; June - 0-75; July - 1.15; August - 0.85

3. MAXIMUM EVAPOTRANSPIRATION (ETm)

Data required are monthly mean ETo m mm/day and the kc values for the given crop over each 30 or 10-day period. Maximum evapotranspiration ETm • kc , ETo.

EXAMPLEGiven: Climatic data collected at station located within an im ga ied areaz

ETo mm/day kcCalculation:ETm nun/day -

mm/month 110 212 314 201 840

May8.9

June9.4 n Au^^t

0.4 0.75 1.15 o \ s s

3.6 7. 1 10.1 6.5110 212 314 201

TabI* 9 V— ~ r P raatu r* (•*'> t" m b r « * FuttCttOn gf M ttB A ir T f ”per9W r« (T i In

9 10 11 12 13 l i 15 16 17 Ifl 19

I t . ! ; 12.'3 M-1 I ’ -O lfe-1 I f O

eaiper*

M « M r

20 21 22 23 21 25 26 27 28 29 30 31 32 33 Y ^

M . Z 2Z . ^ 2 6 ;^ 3H .1 1 1 . ? 3 3 . 6 Jb. 7 »3 7 .B -a o . i ’ A 2 . 4 A A , 3 4 7 -fe 5 0 , 3 ^ . 4 fe2 i £ -

Alao actual vapour pra.aure ( « ! ) can be obtained from this table using available Tdewpoint data. (Eipaiple; Tdewpoini la 18®C: ed la 20.6 mbar)

Table 10 Extra-terrestrial Radiation (Ra) expressed in equivalent evaporation in mm/day

JanNorthern Hemisphere

Feb M ar Apr May June July Aug Sept Oct

6.6 0.6 11.6 16.3 16.6 17.3 16.7 15.2 12.5 9.66.9 9.0 11.0 16.5 16.6 17.2 16.7 15.3 12.8 10.07.6 9.6 12.1 16.7 16.6 17.2 16.7 15.6 13.1 10.67.9 9.8 12.6 16.0 16.5 17.1 16.0 15.5 13.6 10.80.3 10.2 12.8 15.0 16.5 17.0 16.8 15.6 13.6 11.2

8.0 10.7 13.1 15.2 16.5 17.0 16.8^5.7 13.9 11.6 9.3 11.1 1 3 .1 5 .3 16.5 16.8 16.7 15.7 16.1 12.0 9.8 11.5 13.7 15.3 16.6 16.7 16.6 15.7 16.3 12.3

10.2 11.9 13.9 15.6 16.6 16.6 16.5 15.8 16.5 12.610.7 12.3 16.2 15.5 16.3 16.6 16.6 15.8 16.6 13.0

11.2 12.7 16.6 15.6 16.3 16.6 16.3 15.9 16.8 13.311.6 13.0 16.6 15.6 16.1 16.1 l6.1 15.8 16.9 13.612.0 13.3 16.7 15.6 16.0 15.9 15.9 15.7 15.0 13.912.6 13.6 16.9 15.7 15.8 15.7 15.7 15.7 15.1 16.112.8 13.9 15.1 15.7 15.7 15.5 15.5 15.6 15.2 16.6

13.2 16.2 15.3 15.713.6 16.5 15.3 15.6 13.9 16.8 15.6 15.616.3 15.0 15.5 15.516.7 15.3 15.6 15.3 15.0 15.5 15.7 15.3

15.5 15.3 15.3 15.5 15.3 16.715.3 15.0 15.1 15.6 15.3 16.815.1 16.7 16.9 15.2 15.3 15.016.9 16.6 16.6 15.1 15.3 15.116.6 16.2 16.3 16.9 15.3 15.316.6 13.9 16.1 16.8 15.3 15.6

Nov Dec Lat Jan Feb Mar AprSouthern Hemisohcre May June July Aug Sept Oct Nov Dec

7a0 5.7 40° 17.9 15.7 12.5 9.2 6.6 5.3 5.9 7.9 n . o 14.2 16.9 16.37a 5 6.1 38 17.9 15.6 12.8 9.6 7.1 5.8 6.3 8.3 11.4 14.4 17,0 16,38e 0 6.6 36 17.9 16.0 13.2 10.1 7.5 6.3 6.8 8.6 11.7 14.6 17.0 l8 .28. 5 7.2 34 17.8 16.1 13.5 10.5 8.0 6.8 7.2 9.2 12.0 14.9 17.1 18.29- 0 7.8 32 17.8 16.2 13.8 10.9 8.5 7.3 7.7 9.6 12.4 15.1 17.2 1 8 .1

9* 5 8.3 30 17.8 16.6 14.0 11.3 8.9 7.8 8.1 10.1 12.7 15.3 17.3 18.19- 9 8.8 28 17.7 16.6 14.3 11.6 9.3 8.2 6.6 10.4 13.0 15.4 17.2 17.9

10. 3 9.3 26 17.6 16.6 14.4 12.0 9.7 8.7 9*1 10.9 13.2 15.5 17.2 17.810. 7 9-7 24 17.5 16.5 16.6 12.3 10.2 9.1 9.5 11.2 13.4 15.6 17.1 17.711. 1 10-2 22 17.6 16.5 14.8 12.6 10.6 9.6 10.0 11.6 13.7 15.7 17-0 17.5

l ie 6 10,7 20 17.3 16.5 15.0 13.0 11.0 10.0 10.4 12.0 13.9 15-8 17.0 17.412, 0 U . l 18 17.1 16.5 15.1 13.2 Ua4 10.4 10.8 12.3 14.1 15.8 16.0 17.112. 4 11.6 16 16.9 16.6 15.2 13.5 11.7 10.8 11,2 12,6 14.3 15.8 16.7 16.812. a 12.0 14 16.7 16.6 15.3 13.7 12.1 11.2 11.6 12.9 14.5 15.8 16.5 16.613. 3 12.5 12 16.6 16.3 15.4 14.0 12.5 11.6 12.0 13.2 14.7 15.8 16.4 16. j

13. 6 12.9 10 16.6 16.3 15.5 14.2 12.8 12.0 12.4 13.5 14.8 15.9 16.2 16.213. 9 13,3 8 16.1 16.1 15.5 14.4 13.1 12.4 12,7 13.7 14.9 15.8 16.0 16.0U . 2 13.7 6 15.8 16.0 15.6 14.7 13.4 12.8 13.1 14.0 15.0 15.7 15.8 15.7U . 5 U . l 4 15.5 15.8 15.6 14.9 13.8 13.2 13.4 14.3 15.1 15.6 15.5 15.4u . 8 14.4 2 15.3 15.7 15.7 15.1 14.1 13.5 13.7 14.5 15.2 15.5 15.3 15.115. 1 14.8 0 15.0 15.5 15.7 15.3 14.4 13.9 14.1 14.8 15.3 15.4 15.1 14.8

Table 11 Mean Daily Duration of Maximum Possib le Sunshine Hours CN) for Different Months and Latitudes

NortfiemLatitudes Jan Feb M ar Apr M ay June July Aug Sept Oct Nov Dec

SouthernLatitudes July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June

40 9.8 10.7 11.9 13.3 14.4 15.0 14.7 13.7 12.5 11.2 10.0 9 .3A ^

35 10.1 11.0 11.9 13.1 u . o 14.5 14.3 13.5 12.4 11.3 10,3 9 .830 10.4 11.1 12.0 12.9 13.6 14.0 13.9* 13.2 12.4 11,5 10.6 10.2

25 10.7 11.3 12.0 12.7 13.3 13.7 13.5 13.0 12.3 11.6 10.9 10-620 11.0 11.5 12.0 12.6 13.1 13.3 13.2 12.8 12.3 11.7 11.2 10.915 11.3 11.6 12.0 12.5 12.8 13.0 12.9 12.6 12.2 11.8 11.4 n . 210 11.6 11.8 12.0 12.3 12.6 12.7 12.6 12.4 12.1 11.8 11.6 11.55 11.8 11.9 12.0 12.2 12.3 12.4 12.3 12.3 12.1 12.0 11.9 11.80 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0

Table 12 Effect o f Temperature f (T ) on Lontzwave Radiation. (R n l)

T®C 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36

fCT)- 6Tk* 11.0 11.4 11.7 12.0 12 .4 12.7 13.1 13.5 13.8 14.i2 14.6 15.0 15.4 15.9 16,3* 16.7 17-2 17.7 18.1

Table 13 Effect o f Vapour Pressure fCed) on Longwave Radiation (Rn l)

ed mbar 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

fCed) • 0.34 . 0 . 0 4 4 ^ 0.23 .22 .20 .19 .18 .16 .15 .14 .13* .12 . 12 .11 .10 .09 .08 ,08 .07 .06

Table U EffCCl gf Ult Ratio Actual and Maximmn Bright Sunshine Hours fpi/N3 jQP Longwave Radiation CRitl)

.05 .1 .15 .2 .25 .3 .35 .4 .45 -5 .55 .6 .65 .7 .75 .8 .05 -9 -95 l .O

0.10 .15 .19 . 24 , 28 . 33 . 37 . 42 . 46 . 51 .55 - 60 . 64 . 69 . 73 . 78 . 82* .87 . 91 .96 1.0

TaM« 15 v - i - . . n n for A a EflOct o f la d lH f la wt ETo at DKftrtnt To— ra tn r i i Mil AHltMdat

Teepw rtur* ^ 2 4 6 0 10 12 14 16 10 20 22 24 26 20 30 32 34 36 30 40

W M altitude «.66 .69 .00 .02 .03 .040 0.43 .46 .49 .52 .55 .50 .61 .64 .71 .73 .75 .77* .70

soo .40 • 51 .54 .57 .60 .62 .65 .67 .70 .72 .74 .76 .70 .79 .01 .02 .84 .05 .861000 .46 •49 .52 • 55 .61 .64 .66 .69 .71 .73 .75 .77 -79 .00 .02 .03 .05 .06 .072000 •49 • 52 .55 .61 .64 .66 .69 .71 .73 .75 .77 .79 .01 .02 .04 .05 • 86 .07 .66JOOO • 52 • 55 .50 i l l .64 .66 .69 .71 .73 .75 .77 .79 .01 .02 .04 .05 .06 .00 .80 .09

TaM« 16 AdtuiPncnt Factor (c ) in Presented Penman EouatiOD

RHmax - 30k RHmax - 60X RHmax • 90k

Rs mm/day 3 6 9 12 3 6 9 12 3 6 9 12

Uday m/acc Uday/U night - 4.0

0 .06 .90 1.00 1.00 .96 .98 1.05 1.05 1.02 1.06 1.10 1.103 .79 .84 .92 .97 .92 1.00 1.11 1.19 .99 1,10 1.27 1.326 .68 .77 .07 .93 .85 .96 1.11 1.19 .94 1.10 1.26 1.339 .55 .65 .78 .90 .76 .88 1.02 1.14 ,88 1.01 1.16 1.27

UdayAlnight - 3-0

0 .06 .90 1.00 1.00 .96 .98 1.05 1.05 1.02 1,06 1.10 1 .103 .76 .81 .88 .94 .87 .96 1,06 1.12 .94 1.04 1.10 1.286 .61 .60 .81 .80 .77 .88 1.02 1.10 .86 1.01 1.15 1.229 .46 .56 .72 .02 .67 .79 .88 1.05 .78 .92 1.06 1.10

U dayA lnight - 2.0

0 .86 .90 1.00 1.00 .96 .98 1,05 1.05 1.02 1.06 1.10 1.103 -69 .76 .05 .92 .83 .91 .99* 1.05* .89 .98 1.10* 1.14*6 .53 .61 .74 .84 .70 .00 .94 1.02 .79 .92 1.05 1.129 .37 .40 .65 .76 .59 .70 .84 .95 .71 ,81 .96 1.06

Uday/Unight • 1.0

0 .86 .90 1.00 1.00 .96 .98 1.05 1.05 1.02 1,06 1.10 1.103 .64 .71 .02 .89 .78 .86 .94* .99* .85 .92 1.01* 1.05*6 .43 .53 .60 .79 .62 .70 .84 .93 .72 .62 .95 1.009 .27 .41 .59 .70 .50 .60 .75 .87 .62 .72 .87 .96

W. Ra. mm/day W. Rt, mm/day

Fig. I Prediction of ETTo from W.RS for different conditions of mean relative humidity and day time wind.

24

Tabl* 17 Fan Coefficient (kpan) for Class A Pan for D ifferent Groun^cover and Levels o f Mean Relative Humidity

and 2^-hour Windrun

Pan place<l in short green cropped area Pan placed in dry fallow area

RHmean \ low<40

med. 40-70

high>70

low<40

med.40-70

high>70

Windkm/day

Windward side' distance

o f green crop m

Windward side distance

of dry fallow m

Light<175

110

1001000

• 55 .65 .7 .75

.65

.75

.8

.85

.75

.85

.85

.85

110

1001000

.7

.6

.55

.5

.8

.7

.65

.6

.85

.8

.75

.7

Moderate1^") - C25

110

100 1 000

.5

.6

.65

.7

.6

.7

.75*

.8

.65

.75

.8

.8

110

1001000

.65

.55

.5

.45

.75

.65

.6

.55

.8

.7

.65

.6

Strong425-700

110

1001000

.45

.55

.6

.65

.5

.6

.65

.7

.6

.65

.7

.75

110

1001000

.6

.5

.45

.4

.65

.55

.5

.45

.7

.65

.6

.55V ery strong

>7001

10100

1000-

.4

.45

.5

.55

.45

.55,6.6

.5

.6

.65

.65

110

1001000

.5

.45

.4

.35

.6

.5

.45

.4

.65

.55

.5

.45

25

Table 18 Crop Coefficients (kc)

CROPCrop Development stages

Totalgrowingperiod

InitialCrop

development

M idseason

Lateseason

Atharvest

Bananatropical 0 .4 -0 .5 0.7 -0.85 1.0 -1.1 0.9 -1 .0 0.75-0.65 0.7 -0 .8subtropical 0 .5 -0.65 0.8 -0 .9 1.0 -1.2 1.0 -1.15 1.0 -1.15 0,85-0,95

Beangreen 0.3 -0 .4 0.65-0.75 0.95-1.05 0 .9 -0.95 0.85-0.95 0.85-0 .9dry 0•3 -0 .4 0.7 -0 .8 1.05-1.2 0.65-0.75 0.25-0.3 0.7 -0 .8

Cabbage 0.4 -0 .5 0,7 -0 .8 0.95-1.1 0 .9 -1 .0 0.8 -0.95 0.7 -0 .8Cotton 0-4 -0 .5 0.7 -0 .8 1,05-1.25 0.8 -0 .9 0.65-0.7 0.8 -0 .9Grape 0.35-0.55 0.6 -0 .8 0,7 -0 .9 0.6 -0 .8 0.55-0.7 0.55-0.75Groundnut 0.4 -0 .5 0.7 -0.8 0.95-1.1 0.75-0.85 0.55-0.6 0.75-0.8Maize

sweet 0.3 -0 .5 0.7 -0 .9 1.05-1.2 1.0 -1.15 0.95-1.1 0 .8 -0.95grain 0 .3 -0 .5* 0.7 -0.85* 1.05-1.2* 0.8 -0.95 0.55-0.6* 0 .75-0.9*

Oniondry 0.4 -0 .6 0.7 -0 .8 0.95-1.1 0.85-0 .9 0.75-0.85 0.8 -0 .9green 0.4 -0,6 0.6 -0.75 0.95-1.05 0,95-1.05 0.95-1.05 0.65-0 .8

Pea , fresh 0.4 -0 .5 0.7 -0.85 1.05-1.2 1.0 -1.15 0.95-1.1 0.8 -0.95Pepper, fresh 0.3 -0 .4 0.6 -0.75 0.95-1.1 0.85-1 .0 0.8 -0 .9 0.7 -0 .8Potato 0.4 -0 .5 0.7 -0.8 1.05-X.2 0.65-0.95 0.7 -0.75 0 .75-0 .9Rice 1.1 -1.15 1.1 -1 .5 1.1 -1 .3 0.95-1.05 0.95-1.05 1 . 05- 1.2Saffiower 0.3 -0 .4 0,7 -0 .8 1.05-1.2 0.65-0,7 0,2 -0.25 0.65-0,7Sorghum 0.3 -0 .4 0.7 -0.75 1.0 -1.15 0.75-0.8 0 .5 -0.55 0.75-0.85Soyb ean 0.3 -0 .4 0.7 -0.8 1.0 -1.15 0.7 -0.8 0.4 -0 .5 0.75-0.9Sugarbeet 0.4 -0 .5 0,75-0.85 1.05-1.2 0.9 -1.0 0 .6 -0 .7 0.8 -0 .9Sugarcane 0.4 -0 .5 0.7 -1 .0 1.0 -1 .3 0.75-0.8 0 .5 -0 .6 0.85-1.05Sunflower 0 .3 -0 .4 0.7 -0.8 1.05-1.2 0,7 -0 .8 0.35-0.45 0.75-0.85Tobacco 0.3 -0 .4 0.7 -0.8 1.0 -1.2 0.9 -1.0 0.73-0.85 0.85-0.95Tomato 0.4 -0 .5 0.7 -0.8 1.05-1.25 0.8 -0.95 0 .6 -0.65 0.75-0 .9

Water melon 0.4 -0 .5 0.7 -0 .8 0.95-1.05 0.8 -0 .9 0.65-0.75 0.75-0.85Wheat 0.3 -0 .4 0.7 -0.8 1.05-1.2 i' ' - - L 7 5 0.2 -0.25 0.8 -0 .9

Alfalfa

Citrusclean weeding no weed control

O live

0.3 -0 .4 1.05-1.2 0.85-1.05

0.85-0 .9 0 .4 -0 .6

First figure : Second figure;

Under high humidity (RHmin >70%) and low wind (U <5 * "/ »«« )* Under low humidity (RHmin <20%) and

in . ACTU AL EVAPOTRANSPIRATION CETa)

The demand for water by the crop must be met by the water in the soilr via the root system. The actual rate of water uptake by the crop from the soil in relation to its maximum evapotranspiration (ETm) is determined by whether the available water in the •Oil IS adequate or whether the crop will suffer from stress inducing water defic it.

In order to determine actual evapotranspiration (E Ta ), the leve l of the available soil water must be considered. Actual evapotranspiration (ETa ) equals maximum evapotranspiration (ETm) when available soil water to the crop is adequate, or ETa - ETm. However, ETa < ETm when available soil water is limited. Available soil water can be defined as the fraction (p) to which the total available soil water can be depleted without causing ETa to become less than ETm. The magnitude of ETa can be quantified for periods between irrigation or heavy ram, and for monthly periods.

Total available soil water CSa) is defined here as the depth of water in mm/m soil depth between the soil water content at field capacity (S fc or at soil water tension o f 0,1 to 0.2 atmosphere) and the soil water content at wilting point (Sw or at 3oil water tension of 15 atmosphere). Total available soil water (Sa ) can vary widely for soils having a similar texture. A lso, most soils are layered and integrated values of Sa over soil depth should be selected; dense layers restrict water distribution.

As a general indication, Sa mm/m for different soil textures Is:

heavy textured soil 200 mm/mmedium textured soil 140 mm/mcoarse textured soil 60 mm/m

Local information on total available soil water in the root zone will be required. The need for Feld measurements is evident.

I, A D E Q L A i t SOIL W ATER. ETa - ETm

Immediately following irrigation or heavy rain, the actual rate of evapotranspiration (E Ta ) equals maximum evapotranspiration (ETm) where ETm for a given crop is dictated by the evaporative demand of the a ir . As the available soil water is d e p ic t^ , ETa at some point will become less than ETm. The proportion of the total available soil water that can be depleted without causing ETa to become less than ETm is defined by the fraction (p) of the total available soil water (Sa). The value of the fraction (p ) will depend on ( i ) the crop; ( l i ) the magnitude of ETm; and ( i i i ) the soil:

<1 lome crops, such as most vegetables, continuously need re lative lywet soils to maintain ETa • ETm; others, such as cotton and sorghum, can deplete soil water much further before ETa falls below ETm Crops can be grouped according to the fraction (p) to which the available soil water (Sa ) can be depleted while maintaining ETa equal to ETm (Table 19). The tolerable range of the fraction (p) is narrow for crops where the harvested part is in the fleshy or fresh form, such as fruit, vegetable or forage, but it is wider for crops where the harvested part is in the dry form, such as cereals for dry grain, cotton and oil seeds. The value of p may vary with the growth period and in general will be greater during the ripening penod due to the low evapotranspiration (ETm) level

27

caused by a low value of kc. In general, lower depletion levels than calculated arc required during the establishment period.

( i i ) For conditions where BTm is high, p is smaller and the soil is comparatively wet when ETa becomes less than ETm in comparison to when ETm is low. Consequently, the fraction (p) of available soil water over which ETa is equal ETm varies with the level of ETm (Table 20).

( i i i ) Soil water is more easily transmitted to and taken up by the plant roots in light textured than m heavy textured soils. Somewhat higher values of p would seem to apply to light textured soils than than to heavy textured soils. However, considerations of soil texture would add little to accuracy.


a. Total available soil water (D .Sa)from field data or general soil information, determine total available soil water (Sa in mm/m) over the root depth (D in m) or D.Sa in mm/root depth,

b. Soil water depletion (p. D.Sa) when ETa ■ ETmselect soil water depletion fraction (p) for given crop and ETm(Table 19)* Calculate available soil water over root depth (D)or p , 5a . D in mm/root depth when ET a - ETm .

Cm Irrigation interval ( i ) when ETa - ETmcalculate number of days when ETa - ETm by p.Sa,D/ETm.

EXAMPLEGiven: Maize; July; ETm is 10,1 mm/day; soil is medium textured with Sa 140 mm; root depth (D) m July is 1.2 m.

Calculation:

fraction p Tables 19, 20 0.40Sa over root depth Sa.D calc 170available soil water over root depth, ETa - ETm p. Sa.D calc 6b mmirrigation interval (i ) when ETa - ETm p.Sa.D/ETm calc 7

2. LIMITED SOIL WATER , ETa< ETm

Maximum evapotranspiration (ETm) will be maintained until the fraction (p) of the available soil water has been depleted. Beyond this depletion level actual evapotranspiration (ETa) becomes increasingly smaller than ETm until the next irrigation or heavy ram. When ETa < ETm, the magnitude of ETa will depend on the rcmaiolng available soli va ter ( l-p )S a .D , and on ETm. The remaining available soil water is related to the crop group (Table 19), to ETm ( i .e . the fraction p) and to the total available soil water over ^be root depth (Sa.D ), Appl>dng an adaptation of the formulation bv Rijtema and Aboukhaled (1975) given in Appendix 1, ETa can be quantified for the interval between imgauon or heavy rain (Table 21) and for monthly periods (Table 22).

2 8

For practical afmlication, the information can be used to calculate the effect of available soil water on ETa, and also to determine ETa for the period since last irrigation or heavy ram and for monthly periods when monthly irrigation supply and rainfall are known. The calculated results are relevant to predict the effect of i r r i gation schedules on ETa. The need to check the presented information through local available field data and comparison with other methods to determine ETa is stressed.

Table 19 Crop^rou, according to Soil Water Depletion

Group Crops

onion, pepper, potatobanana, cabbage, grape, pea, tomatoalfalfa, bean, citrus, groundnut, pineapple, sunflower, watermelon, wheatcotton, maize*, olive, safflower, sorghum, soybean, sugarbeet, sugarcane, tobacco

Table 20 Soil Water Depletion Fraction (p) for Crop Groupsand Maximum Evapotranspiration (ETm)

Crop ETm mm/dayGroup 2 3 5 6 7 0 9 10

1 0.50 0.425 0.35 0.30 0.25 0.225 0.20 0.20 0.1752 0.675 0.575 0.475 0.40 0,35 0.325 0.275 0.25 0.2253 0.80 0.70 0.60 0.50 0.45 0.425 0.375 0.35 0.30

- 0.875 0.80 0.70 0.60 0.55 0,50 0.45 0.4250.40*

2.1 ETa over Ir r igation Interval


a. Total available soil water (D.Sa)from field data or general information on crop and soil determinetotal available soil water (Sa) over the root depth (D) or D.Sa in nun/root depth.

b. Soil water depletion fraction (p) when ETa - ETma#ldct p for given crop and level of ETm (Table 20).

c. Actual evapotranspiration (ETa)select mean ETa over irrigation interval for value of ETm, p and D.Sa aab le 21).

29

e x a m p l e

<^ivenI M a ize ; July; ETm • 10,1 mm/dayj soil is moHium tcKturcH wwh Sa - 140 mm/m; root depth (D ) in July i t 1.2 m.

Calculation:

total available soil waterfraction p ETa

D .Sa calcTable 20

by interpolation Table 21

170 mm/root depth0.40

irrigation in torval. days 8 10 12 16 20 24 30mean ETa maize, mm/day 9.8 9.4 9.0 5.0 7.1 6.2 5.3

Similar calculations are made for when ETm maize is 7 and 4 mm/day. Results of calculating ETa and available soil water depletion for different durations of the irrigation interval are given in the figure below. This shows that at lower ETm values the irrigation interval with ETa - ETm can be extended (F igure 2).

10

.2UJ 4

2

ETm = 10

ETm = 4

4-10 12 (4 e 1 8 2 0 22 2 4 2 6 2 8 3 0

doyt after irriyotioA

ovoiiol>i«•oHweter

16 « 20 22 24 26 28Ooys oft«r irrigonoe

^^8* 2 Mean actual evapotranspiration (L 1 a) and available toil water(Sa .D ) over time after irrigation for different values of maximum

evapotranspiration (ETm)

Table 21 Mean Actual Evapotranspiration (E Ta) in mm/day over the Irrigation Interval for Different Yields of ETm (mm/day), D .Sa (mm) and p (fraction)

30

ETm - 2.0 mm/day

D.Sa P 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 35 40

25 0.2 2.0 2.0 1.8 1.7 1.6 1.4 1.3 1.2 1.2 1.1 1.0 0.9 0.9 0.8 0.8 0.7 0.60.^ 2.0 2.0 2.0 1.9 1.7 1.6 1.5 1.4 1.2 1.2 1.1 1.0 0.9 0.9 0.8 0.7 0.60.6 2.0 2.0 2.0 1.9 1.7 1,6 1.5 1.3 1.2 1.1 1.0 1.0 0.9 0,8 0.7 0.60.6 2.0 2.0 2.0 1.9 1.7 1.5 1.4 1.3 1.1 1.0 1.0 0,9 0.8 0.7 0.6

50 0.2 2.0 2.0 2.0 2.0 1.9 1.8 1.8 1,7 1.6 1.6 1.5 1.4 1.4 1.3 1.3 1.2 1.10,1 2.0 2.0 2.0 2.0 1.9 1.9 1.8 1.7 1.7 1.6 1.5 1.5 1.4 1.3 1.10*6 2,0 2.0 2.0 2.0 2.0 1.9 1.8 1.7 1.7 1.6 1.5 1.4 1.20.8 2.0 2,0 2.0 2.0 1.9 1.8 1.7 1.6 1.4 1.2

100 0.2 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2,0 1.9 1.9 1.9 1.8 1.8 1.7 1.7 1.6 1.60.4 2.0 2,0 2.0 2,0 2.0 2.0 2,0 1.9 1.9 1.8 1.70.6 2.0 2.0 2.0 2.0 2.0 1.90.8 2.0 2,0 2.0 2.0

150 0.2 2.0 2.0 2.0 2.0 2.0 2,0 2.0 2.0 2.0 2.0 2.0 2.0 1.9 1.9 1.9 1.8 1.80.4 2.0 2.0 2.0 2.0 2.0 2.0 1.90.6 2.0 2,0 2.00.8 2.0 2.0

200 0.2 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.9 1.90.4 2.0 2.0 2,0 2.00.6 2.0 2.00.6 2.0 2.0

300 0.2 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2,0 2.0 2.0 2.0 2.0 2.0 2.0 2.00.4 2,0 2.00.6 2.0 2,00.8 2.0 2.0

ETm - 4.0 mm/day

25 0.2 3.9 3.4 2.9 2.5 2.2 1.9 1.7 1,5 1.4 1.2 1.1 1.0 0.9 0.9 0.8 0.7 0.60.4 4.0 3.7 3.2 2.7 2,3 2,0 1.7 1.5 1.4 1.3 1.1 1.0 1.0 0.9 0,8 0.7 0.60.6 4.0 4.0 3.5 2.9 2.4 2.1 1.8 1.6 1.4 1.3 1.1 1.0 1.0 0.9 0.8 0.7 0.60.8 4.0 4.0 3.8 3.1 2.5 2.1 1.8 1.6 1.4 1.3' 1.1 1.0 1.0 0.9 0,8 0.7 0.6

50 0.2 . 4.0 3.9 3.6 3.4 3.1 2.9 2.7 2.5 2.3 2.2 2.0 1.9 1.8 1.7 1.6 1.4 1.20.4 4.0 4,0 4.0 3.7 3.5 3.2 2.9 2.7 2,5 2.3 2.1 2.0 1.9 1.7 1.6 1.4 1.20.6 4.0 4 .0 4.0 3,8 3.5 3.2 2.9 2.6 2,4 2.2 2.1 1.9 1.8 1.6 1.4 1.20.8 4.0 4.0 4,0 3.8 3.4 3,1 2.8 2,5 2.3 2.1 1-9 1,8 1.6 1.4 1.2

100 0.2 4.0 4.0 4.0 3.9 3.8 3.6 3.5 3.4 3.2 3.1 3.0 2.9 2.8 2.7 2.6 2.3 2.20.4 4.0 4.0 4.0 4.0 4.0 3.9 3.7 3.6 3.5 3.3 3.2 3.1 2.9 2.8 2.5 2.30.6 4.0 4.0 4.0 4.0 3.9 3.8 3.6 3.5 3.3 3.2 3.0 2.7 2.40 .8 4.0 4.0 4 .0 4.0 3.9 3.8 3.6 3.4 3.2 2.8 2.5

ISO 0.2 4.0 4.0 4.0 4.0 4.0 3.9 3.8 3.7 3.6 3.5 3.5 3.4 3.3 3.2 3.1 2.9 2.70.4 4.0 4.0 4.0 4.0 4.0 4 .0 3.9 3.8 3.7 3.7 3.6 3.5 3.2 3,00.6 4 .0 4.0 4.0 4.0 4.0 3.9 3.9 3,8 3.5 3.30.8 4.0 4.0 4.0 4,0 4.0 3.8 3.6

200 0.2 4.0 ' r< :.o 4.0 3.9 3.9 3.8 3.8 3.7 3,6 3.6 3.5 3.4 3.3 3.10.4 4.1 4.0 4.0 4.0 4 .0 4.0 4.0 4.0 3.9 3.9 3.8 3.6 3.50.6 4.0 4.0 4.0 4.0 4.0 3.9 3.80.8 4.0 4.0 4.0 4.0

300 0.2 4.0 4.0 4.0 4.0 4.0 4,0 4.0 4.0 4 .0 4.0 3.9 3.9 3.9 3.8 3.8 3.7 3.50.4 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 3.90.6 4.0 4.0 4.00.8 4.0 4.0

3J

Tabl« 21 Conunucd

ETm * 6>,0 mm/day

D .Sa P 2 2 6 8 10 12 12 16 18 20 22 24 26 28 30 35 20

25 0.2 5.5 2.3 3 .5 2.8 2.2 2.0 1.8 1.6 1.2 1.2 1.1 1,0 l.O 0 .9 0 .8 0.7 0.60,/ 5.9 2 .8 3.7 3.0 2.5 2.1 1.8 1.6 1.2 1.3 1.1 1.0 1.0 0.9 0 .8 0.7 0.60 .6 6 .0 5.2 2 .0 3.1 2.5 2.1 1.8 1.6 1.2 1,3 1.1 1.0 1.0 0 .9 0 .8 0.7 0.60.6 6.0 5.7 2.1 3.1 2.5 2.1 1.8 1.6 1.2 1.3 1.1 1.0 1.0 0.9 0 .8 0.7 0,6

50 0.2 6.0 5.5 2 .9 C.3 3.9 3.5 3.1 2.8 2.6 2.2 2.2 2.0 1.9 1.8 1.7 1.2 1.30,/ 6.0 5.9 5.^ 2.8 2.2 3.7 3.3 3.0 2.7 2.5 2.2 2.1 1.9 1.8 1.7 1.2 1.30.6 6.0 6.0 5.9 5.2 2.6 2.0 3.5 3.1 2.8 2.5 2.3 2.1 1.9 1.8 1.7 1,5 1.30.8 6,0 6.0 6.0 5.7 2.9 2.1 3.6 3.1 2.8 2.5 2.3 2.1 1.9 1.8 1.7 1.2 1.3

100 0.2 6,0 6.0 5.8 5.5 5.2 2.9 2.6 2,3 2.1 3.9 3.7 3 .5 3.3 3.1 3.0 2.6 2.20./ 6 .0 6.0 6.0 5.9 5-7 5.2 5.1 2.8 2 .5 2.2 2.0 3.7 3.5 3.3 3.1 2.8 2.20.6 6,0 6.0 6.0 6.0 5.9 5.6 5.2 2.9 2.6 2.3 4.0 3.7 3.5 3.3 2.0 2.50.8 6,0 6.0 6.0 6.0 5.7 5.3 2.9 2 .5 4.1 3.8 3.6 3.3 2.9 2.5

150 0.2 6.0 6,0 6.0 5.8 5.7 5.5 5.3 5.1 2 .9 2.7 4 .5 4.3 2.2 2.0 3.9 3.5 3.20.2 6.0 6.0 6.0 6.0 5.9 5.8 5.6 5.2 5.2 5.0 4.8 2.6 2.2 2.2 3.0 3.30.6 6 .0 6.0 6.0 6.0 6.0 5.9 5.7 5.5 5.2 5.0 2.8 2 .6 2.1 3.60.8 6,0 6,0 6.0 6.0 5.9 5.7 5.2 5.1 2,9 2.2 3.7

200 0.2 6.0 6.0 6.0 6.0 5.9 5.8 5.6 5.5 5.3 5-2 5.0 4.9 2.7 2.6 2.2 2.1 3.90.2 6.0 6.0 6.0 6.0 6.0 5.9 5.8 5.7 5.6 5.4 5.2 5.1 2 .9 2.6 2.20.6 6.0 6.0 6,0 6 .0 6,0 6.0 5.9 5.7 5.6 5.2 5.0 2.60.8 6.0 6.0 6.0 6.0 6.0 5.9 5.2 2 .9

300 0.2 6.0 6.0 6.0 6.0 6.0 6.0 5.9 5.8 5.8 5.7 5.6 5.5 5.2 5.3 5.2 2.9 2.70.2 6.0 6.0 6.0 6.0 6.0 6.0 6.0 5.9 5.9 5.8 5.7 5.2 5.20.6 6.0 6.0 6.0 6.0 6 .0 6.0 5.9 5* 70 .8 6.0 6.0 6 .0 6.0

ETm - fCo mm/day

25 0.2 6.7 5.0 3.8 3.0 2.5 2.1 1.8 1.6 1.2 1.3 l . l 1.0 1.0 0.9 0.8 0.7 0.60.2 7.5 5.2 2.0 3.1 2.5 2.1 1.8 1.6 1.2 1.3 1.1 1,0 1.0 0.9 0.8 0.7 0.60 .6 . 8,0 5.8 2.1 3.1 2.5 2.1 1.8 1,6 1.2 1.3 1.1 1.0 1.0 0.9 0,8 0.7 0 .60.8 8,0 6.1 2.2 3.1 2.5 2.1 1.8 1,6 1.4 1.3 1.1 1,0 1.0 0 .9 0.8 0.7 0.6

50 0.2 7.8 6.7 5.8 5.0 2.3 3.8 3,2 3.0 2.7 2.5 2.2 2.1 1.9 1.0 1.7 1.2 1.30 .2 7.9 7.5 6.2 5.2 2.6 2.0 3.5 3.1 2.8 2.5 2.2 2.1 1.9 1.8 1.7 1.2 1.30.6 8.0 8.0 7.0 5.8 2.8 2.1 3.6 3.1 2.8 2.5 2.3 2.1 1.9 1.0 1.7 1.2 1.30.8 8.0 8.0 7.6 6.1 5.0 2.2 3.6 3,1 2,8 2.5 2.3 2.1 1.9 1.8 1.7 1.2 1.3

100 0.2 8,0 7.8 7.3 6.7 6.2 5.8 5.3 5.0 2.6 2.3 4 .0 3.8 3.6 3.2 3.2 2.8 2 .50.2 8,0 8.0 7.9 7.5 6,9 6.2 5.9 5.2 5.0 2.6 4.3 4.0 3.7 3.5 3.3 2.8 2.50.6 8.0 8.0 8.0 8.0 7.6 7.0 6.2 5.8 5.3 2.9 4 ,5 4.1 3.8 3.6 3.3 2,9 2.50.8 8.0 8.0 8.0 7.6 6.9 6.1 5.5 5.0 4 ,5 4.1 3.8 3.6 3.3 2.9 2.5

150 0.2 8.0 8.0 7.8 7.5 7.1 6.7 6,2 6.1 5.8 5.5 5.2 5.0 2.7 2.3 3.9 3.50.2 8,0 8.0 6.0 8.0 7.8 7.5 7.1 6.7 6.2 6.0 5,7 5.2 5.1 2 .8 2.6 2.1 3.60.6 8.0 8.0 8.0 6.0 7.7 7.2 7.0 6.6 6,2 5.8 5.5 5.1 2.6 2.2 3.70.8 8.0 8.0 8.0 7.9 7.6 7.1 6,6 6.1 5.7 5.3 5.0 2.3 3.7

200 0.2 8.0 8.0 8.0 7.8 7.5 7.2 7.0 6.7 6.5 6.2 6.0 5-7 5.5 5.3 5.1 2.7 2.30.2 e .o 8,0 8.0 8.0 7.9 7.7 7.5 7.2 6 .9 6.6 b.2 6.1 5.9 5.6 5.1 2,60.6 6,0 8.0 8.0 8.0 8.0 7.8 7.6 7,3 7.0 6.7 6.2 6.1 5.2 2.80.8 e .o 8.0 6.0 8.0 7.9 7.6 7.2 6.9 6.5 5.7 5.0

300 0.2 8,0 8.0 6.0 8.0 7.9 7.8 7.6 7.5 7.3 7.1 6 .9 6.7 6.6 6.2 6.2 J.8 5*50.2 8,0 8.0 0.0 6.0 8.0 8.0 7.9 7.8 7.6 7.5 7.3 7.1 6.9 6 .5 6.00.6 8.0 0.0 8.0 8.0 8,0 8,0 7.9 7.7 7.6 7,1 6.70.8 8.0 6.0 6.0 8.0 6.0 7.7 7.1

32

Tabic 21 Continued

E T * - 10.0 mm/day

D .Sc 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 35 40

25 0.2 7.8 5.4 4.0 3.1 2.5 2.1 1.8 1.6 1.4 1.3 1.1 1.0 1.0 0.9 0,8 0.7 0.60.4 8,7 5.7 4.1 3.1 2.5 2.1 1,8 1.6 1.4 1.3 1.1 1.0 1.0 0.9 0.8 0.7 0.60.6 9<5 6.0 4.2 3.1 2.5 2.1 1.8 1.6 1.4 1.3 1.1 1.0 1.0 0.9 0.8 0.7 0.60.6 10.0 6.2 4.2 3.1 2.5 2.1 1.8 1.6 1.4 1.3 1.1 1.0 1.0 0.9 0.8 0.7 0.6

50 0.2 9.4 7.8 6.4 5.4 4.6 4,0 3.5 3.1 2.8 2,5 2.3 2.1 1.9 1.8 1.7 1.4 1.30.4 10.0 8.7 7.0 5.7 4.8 4.1 3.5 3.1 2.8 2.5 2.3 2.1 1.9 1.8 1.7 1.4 1.30.6 10.0 9.5 7.6 6.0 4.9 4.2 3.6 3.1 2.8 2.5 2.3 2.1 1.9 1.8 1.7 1.4 1.30.6 10.0 10.0 8.1 6.2 5.0 4.2 3.6 3.1 2.8 2.5 2.3 2.1 1.9 1.8 1.7 1.4 1.3

100 0.2 10.0 9.4 6.6 7.8 7.1 6.4 5.9 5.4 5.0 4.6 4.3 4.0 3.7 3.5 3.3 2.8 2.50.4 10.0 10.0 9.5 8.7 7.8 7.0 6.3 5.7 5.2 4.8 4.4 4.1 3.8 3.6 3.3 2.8 2.50.6 10.0 10.0 10.0 9.5 8.5 7.6 6.8 6.0 5.4 4.9 4.5 4.2 3.8 3.6 3.3 2.9 2.50.6 10,0 10.0 10.0 9.3 8,1 7.1 6.2 5.6 5.0 4 .5 4.2 3.9 3.6 3.3 2.9 2.5

150 0.2 10.0 9.9 9.4 8.9 8.3 7.8 7.3 6.8 6.4 6.0 5.7 5.4 5,1 4.8 4.6 4.0 3.70.4 10,0 10.0 10.0 9.7* 9 .2* 8.7* 8.1*' 7.5* 7.0 6.6* 6.1 5.7* 5.4 5.1 4.8*'4 .2 3.70 .6 10,0 10.0 10.0 9.9 9.5 8.9 8.2 7.6 7.0 6.5 6.0 5.6 5.3 4.9 4.3 3.70 .8 10.0 10.0 10.0 10.0 9.6 8.9 8.1 7.4 6.8 6.2 3.8 5.4 5.0 4.3 3.7

200 0.2 10.0 10.0 9.8 9.4 9.0 8.6 8.2 7.8 7.4 7.1 6.7 6.4 6.1 5.9 5.6 5.1 4.60.4 10.0 10.0 10.0 10.0* 9.8"* 9.5* 9.1* 8.7* 8.2 7.6* 7.4 7 .0*6 .7 6.3 6 .0* 5.4 4.80 .6 10.0 10.0 10.0 10.0 9.8 9.5 9.0 8.5 8.1 7.6 7.2 6.8 6.4 5.6 4.90.8 10.0 10.0 10,0 10.0 9.8 9.3 8.7 8.1 7.6 7.1 6.6 5.7 5.0

300 0.2 10.0 lO.O lO.O 9.9 9.7 9.4 9.2 8.9 8.6 8.3 8.0 7.6 7.5 7.3 7.1 6.5 6.00.4 10.0 10.0 10.0 10.0 10.0 9.9 9.7 9.5 9.2 8.9 8.7 8.4 6.1 7.8 7.1 6.50.6 10.0 10.0 10,0 10.0 10.0 9.9 9.7 9.5 9.2 8.9 8.5 7.7 7.00.8 10.0 10.0 10.0 10.0 10.0 9.9 9.6 9.3 8.3 7.4

33

2./ h i a over Monthly PericKjg

For reconnaissance and prelim inary planning purpose* an estimate o f mean monthly actual evapotranspiration (E T a ) fo r a given crop can be obtained using the available soil water index (A S l ) . The ASI indicates the p a n of the month when available soil water is adequate for meeting full crop water requirements (E Ta - ETm), A combination of AS I value, maximum evapotranspiration (ETm ) and remaining available soil water [C l-p )Sa .D l provides an estimate of the mean monthly ETa.

AS l - lli-t Pe . Wb . [ ( l .D )S a .Pmonthly ETm

where:

Iti “ Dct monthly irr iga tion application, mm/monihP e - e ffect ive ra in fa ll, mm/monthWb - actual depth of available soil water at beginning o f the

month, mm/root depth ( l - p )S a .D “ depth of remaining available soil water when E T a< ETm,

mm / root depth ETm - maximum evapotranspiration, mm/month

F or the AS l it is assumed that In + Pe when equal o r smaller than 30 ETm will fully contribute to the evapotranspiration and no deep percolation or runoff will occur; also mean monthly ETa is only affected by the total o f In, Pe and Wb and not by their distribution over the month.

AS l can be grea ter than one, o r smaller than zero , When AS l >1, then ETa - ETm; when A S 1 < 0 then ETa/ETm is so small that crop growth is hardly possible except when ETm is low and the remaining available soil water ( ( l - p )S a .D l is high.

CA LC U LA T IO N PROCEDURE

a. Available soil water index (A S l )DctcrTTnno: In 4 Pc + Wb - [( l-D )Sa.D .

monthly ETm

b. Actual evapotranspiration (E T a )Select monthly mean ETa in mm/day from the calculated A S I ,the remaining available soil water ( l - p )S a .D l in mm/root depth whenE T a < ETm, and maximum evapotranspiration (ETm ) in mm/day (Tab le 22)

EX AM PLEG iven : M a ize ; July; ETm is 10.1 mm/day; soil is medium lextured with 5a 140 mm/m; root depth (D ) i s 1.2 m .net irr igation application (In) • 145 Bvm/moniheffect ive ra in fa ll (P e ) - 20 mm/monthactual depth of available water at beginning o f month (Wb) - 40 mmIn ♦ P e ♦ Wb - 205 mm/monih

Calculation:fraction p Tables 19, 20 • __available soil water when E T a < E T m ( l - p )S a .D calc * iAS l (205-100)/(31 x lO.O) calc •ETa Table 22 • 6 .2 m«/day

34

Tablr 22 Monthly Mean Actual Evapotranspiration (ETa in nun/day) for A S l, Remaining Available Soil Water when ETa < ETm ( [(1 -p ) Sa.D ) in mm/root depth) and Maximum Evapotranspiration (ETm

in mm/da\ )

AS! - 0.83 ASl - 0.67 ASl - 0.5(1 -p)Sa. D ETm, mm/day ETm, mm/dav ETm , mm/day

mm/root deoth 2 4 6 8 IQ 2 4 6 8 10 2 4 6 8 IQ25 1.9 3.8 5.6 7.3 9.1 1.3 3.3 4,8 6.1 7.5 1.6 2.8 3.8 4.8 5.850 2.0 3.9 5.7 7.6 9.4 1.9 3.6 5.2 6.7 8.1 1.7 3.2 4.4 5.5 6.5

100 2.0 3.9 5.9 7.8 9.6 1.9 3.8 5.5 7.2 8.8 1.9 3.5 5.0 6.3 7.6150 2.0 4.0 5.9 7.8 9.7 2.0 3.8 5.7 7.4 9.1 1.9 3.7 5.3 6.7 8.1200 2.0 4.0 5.9 7.9 9.8 2.0 3.9 5.7 7.5 9.3 1.9 3.7 5.4 7.0 8.5

ASl - 0.33 ASl - 0.17 ASl = 0(l-p )S a .D

mm/root deothETm,

2 4mm/day

6 8 10 2ETm

4, mm/day

6 8 10 2ETm

4, mm

6/day

8 1025 1.3 2.1 2.8 3.5 4.2 1.1 1.5 1.8 2.2 2.5 0.8 0.8 0.8 0.8 0.850 1.6 2.7 3.5 4.3 5.0 1.4 2.1 2.8 3.0 3.3 1.2 1.5 1.6 1.7 1.7

100 1.8 3.2 4.3 5.3 6,2* 1.7 2.8 3.6 4.2 4.7 1.5 2.3 2.8 3.0 3.2150 1.8 3.4 4.7 5.9 7.0 1.7 3.1 4.2 5.0 5.7 1.7 2.7 3.5 4.0 4.3200 1.9 3.5 5.0 6.3 7.5 1.8 3.3 4,5 5.5 6.4 1.7 3.0 4.0 4.7 5.1

IV . ACTUAL YIELD OTa)

When water supply does not meet crop water requirements, actual evapotranspiration (ETa) will fall below maximum evapotranspiration (ETm) or ETa< ETm. Under this condition, water stress will develop m the plant which will adversely affect crop growth and ultimately crop yield. The effect of water stress on growth and yield depends on the crop species and the variety on the one hand and the magnitude and the time of occurrence of water deficit on the other. The effect of the magnitude and the timing of water deficit on crop growth and yield is of major importance in scheduling available but limited water supply over growing periods of the crops and in determining the pnprity of water supply amongst crops during the growing season.

Crops vary in their growth and yield response to water deficit. When crop water requirements are fully met by available supply (ETa - ETm), the amount of total dry matter and yield produced per unit of water <Vg/m3) varies with crop. This can be expressed as the water utilization efficiency in kg/m for total dry matter (Em) and harvested yield (Ey). Crops have different growth rates and crop water requirements; also the portion of the total dry matter that is harvested as yield varies with the crop (harvest index. Table ?)• When ETa ■ ETm, these differences in growth and yield result in differences in Em and Ey, For example, Em for groundnut is about 1,6 and for maize about 2.5; with harvest index (cH) for groundnut (unshelled) equal to 0.35 and for maize 0,40 and taking into account the moisture percentage of the harvested part specific to the crop, the value of Ey for groundnut is about 0.65 and for maize about 1,15. However, as Ey also depends on the harvest index (cH) and the moisture percentage of the harvested part, a high Em does not always lead to a high Ey.

When water supply does not meet crop water requirements, or ETa < ETm, crops vary in their response to water deficits. In some crops there is an increase in water utilization efficiency (Ey) whereas for other crops Ey decreases with increase in water deficit. For example, with a water deficit spread equally over the total growing season, Ey will decrease for maize and increase somewhat for sorghum under similar climatic conditions. Although yield per unit area Ckg/ha) for both crops will be lower when water supply is limited, the yield reduction will be greater in the case of maize.

When water deficit occurs during a particular part of the total growing period of a crop, the yield response to water deficit can vary greatly depending on how sensitive the crop is at that gro>»^ period. In general, crops are more sensitive to water deficit during emergence, flowering and early yield formation than they are during early (vegetative, after establishment) and late growth periods (ripeningXTable 23).

However, the yield response to water deficit can vary among varieties of the same crop. In general, high producing varieties are also the most sensitive in their response to water, fertilizer and other agronomic inputs. On the other hand, low producing varieties with little response to water may be more suitable for ramfed crop production in areas which are prone to drought. To attain high yields under irrigation, it is necessary to use h i^ producing and most responsive varieties to water so that high water utilization efficiency for harvested yield (Ey) is obtained. For instance, many traditional maize varieties produce 2 to 3 ton/ha gram under erratic rainfall conditions and 4 to 5 ton/ha grain under full irrigation; this compares with yields of 8 to 10 ton/ha grain of high producing varieties under full irrigation but with drastically reduced yields under erratic rainfall or poor irrigation. Efforts directed toward increased yields by improved irr iga tion must be based on the use of high producing varieties obtained through local field evaluation and selection trials.

The response of yield to water cannot be considered m isolation from all the other agronomic factors, such as fertilizers, plant density and crop protection, because these factors also determine the extent to which actual yield (Ya) approaches maximum yield (Ya )«

36

Tabic 23 Sensitive Growth Periods fo r Water Deficit

A lfalfa

Banana

Bean

Cabbage

Citrusgrapefruitlemon

orange

Cotton

Grape

Groundnut

Maize

Olive

Onion

Pea

Pepper

Pineapple

Potato

Rice

SafflowerSorghum

Soybean

Sugarbeet

Sugarcane

Sunflower

Tobacco

Tomato

Watermelon

Wheat

just a fter cutting (and for seed production at flowering)

throughout but particu larly during firs t ; » r t o f vegetative pen od , flowenng and yield formation

flowering and pod fillin g ; vegetative period not sensitive when followed by ample water supply

during head enlargement and ripening

flowering and fruit set > fruit enlargementflow enng and fruit set > fruit enlargement; heavy flowering may be induced by withholding irrigation jusi before flowering flow enng and fruit set > fruit enlargement

flowering and boll formation

vegetative penod , particu larly during shoot elongation and flowering > fruit filling

flowenng and yield formation, particu larly during pod setting

flowenng >grain filling ; flowering very sensitive i f no p r io r water defic it

just p rior flowering jna weld formation, particu larly during the period o f stone hardening

bulb enlargement, particu larly during rapid bulb growth >vegetative penod (and for seed production at flow enng)

flowering and yield formation >vegetative , npemng for d ry peas

throughout but particu larly just p r io r and at start o f flowering

during period o f vegetative growth

penod of stolonization and tuber initiation, yield tormauon > early vegetative period and ripening

dunng penod of head development and flowering > vegetative period and npening

seed filling and flowenng > vegetativeflowering yield formation >vegeta tivc ; vegetative period less sensitive when followed by ample water supply

yield formation and flowering; particu larly dunng pod development

particu larly firs t month after emergence

vegetative penod , particu larly during period o f tillering and stem elongation > yield formationflowenng > yield formation -> late vegetative, particu larly period of bud devcTopmeniperiod of rapid grown. - tonuution uud ripening

flowering > yield formation > vecetative penod , p a m c ila r lv during and pisl after transplantingflow enng, fruit filling > vegetative period, particularly dunng vine developmentflowering > yield formation > vegetative penod ; winter wheal less sensltlv* than spnng wheat

V. Y IELD RESPONSE FACTOR Ckv)

The response o f y ield to water supply is Quantified through the yield response factor (Vy) which re la tes re la t iv e y ie ld d ecrease ( 1 -Ya/Ym ) to re la t iv e evapotranspiration de fic it (1 -E T a/E Tm ), W ater de fic it o f a given magnitude, expressed in the ratio actual evapotranspiration (E T a ) and maximum evapotranspiration (E T m ), may e ither occur continuously o v e r the total growing period of the crop o r it may occur during any one o f the individual growth per iods ( i . e . establishment (0 ) , vegetative (1 ) , flow ering (2 ), yield formation (3 ) , o r ripening (4 ) period ). The magnitude o f water de fic it r e fe r s in the form er to the de fic it in relation to crop water requirements o ve r the total grow ing period of the crop and in the la tter to the de fic it m relation to the crop water requirements o f the individual growth period (Tab le 24).

The genera lized e ffect o f water de fic it on crop y ie ld is schematically presented fo r both the total grow ing period and the individual growth periods (F ig u re 3)- genera l, for the total grow ing penod , the d ecrease in yield is proportionally less wilh the increase in water de fic it ( ky < 1) for crops such as a lfa lfa , groundnut, sa ff low er and sugarbeet (Group I ) while it is proportionally g rea te r (Vy > 1 ) fo r crops such as banana, maize and sugarcane (Group IV ) , F or the individual growth periods the decrease in yield due to water de fic it during that growth period is re la t iv e ly small fo r the vegetative (1 ) and ripening period (4 ) and re la t iv e ly la rge fo r the f low er ing (2 ) and y ie ld formation (3 ) per iod . W ater de fic it during a particu lar growth period can also be expressed as a water de fic it o v e r the total grow ing period when the relationship between the maximum evapotranspiration (E Tm ) of that growth penod and ETm of the total grow ing period is known (se e F igures in Pa rt B ).

The ky values fo r most crops a re derived on the assumption that the relationship between re la t iv e y ie ld (Ya/Ym ) and re la t ive evapotranspiration (E Ta/E Tm ) is linear and IS valid fo r water de fic its of up to about 50 percent o r 1 - ETa/ETm - 0*5* The values of ky are based on an analysis o f experimental fie ld data cover ing a wide rangjc o f growing conditions (s ee B ib liography). The experimental results used represent high- producing crop va r ie t ie s , well-adapted to the grow ing environment and grown under a high leve l o f crop management.

An evaluation o f fie ld experimental data indicates some scatter m ky values which is due to experimental inadequacies, and variations in climate, leve l o f evapotranspiration and so il. Separation of ky according to the variation in these factors did not add to the accuracy obtainable. Since no standard re fe ren ce values are availab le fo r comparison, the re liab il ity o f the presented ky values (Tab le 24) is assumed lo be sim ilar to that o f the outcome o f the analysis o f the field expenmental resu lts ; in most cases 80 to 85 percent o f the yield variation due to d ifferent water treatments can be explained. In the final evaluation o f the ky va lues, from the field experimental data, use is a lso made o f known y ie ld responses to soil sa lin ity , the depth of the groundwater table and agronomic and irr igation p rac t ices .

The magnitude and duration of water de fic it expressed as re la t ive evapotranspiration de fic its (1 - ETa/ETm ) are made to correspond closely to the individual crop growth per iods . Analys is o f the availab le field experimental data in terms of the more prec ise ly defined s tress-day and drought indices proved d iff icu lt .

Application o f the yield response factor (k y ) fo r planning, design and operation of irr iga tion p ro jec ts allows quantification o f water supply and water use in terms o f crop yield and total production for the p ro ject area . Under conditions of limited water distributed equally o ve r the total growing season, involving crops with d ifferent ky values, the crop with the higher ky value w ill su ffer a g rea te r yield loss than the crop with a low er ky value. Both the likely losses in yield and the adjustments required in water supply to minimize such losses can W quantified. S im ila r ly , such a quantification is

38

•St Mpoinmmition diicit

11

111

IV

alfalfagroundnutsafflowersugarbeet

alfalfa sorghumcabbage soybeancitrus sugarbeetcotton sunflowergrape tobacco

wheat

bean potatocitrus tomatoonion water melonpea wheatpepper

bananamaizesugarcane

.Ua. Retolive evopotron*ptrolton delicti

10 0 5 0

Ftg* 3 Generalized relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration

(1 - ETa/ETm)

Table 24 Yield Response Factor Cky)

V e cetati ve period (1 ) F lowering Yield Ripening TotalCrop early

( la )late( lb ) total period

(2)formation

(3 ) (4)growingperiod

Alfalfa 0 .7-1 .1 0.7 -1 .1Banana 1.2-1.35Bean 0.2 1.1 0.75 0,2 1.15

Cabbage 0.2 0.45 0 .6 0.95Citrus 0.8-1 .1

Cotton 0.2 0 .5 0.25 0.85

Grape 0.85

Groundnut 0.2 0.8 0.6 0.2 0.7

M aize 0.4 1.5* 0 .5 0.2 1.25*

Onion 0.45 0.8 0.3 1.1

Pea 0.2 0 .9 0.7 0.2 1.15

Pepper 1.1

Potato 0.45 0.8 0.7 0.2

Safflower 0.3 0.55 0.6 * c

Sorghum 0.2 0.55 0.45 0.2 0.9

Soybean 0.2 0.8 1.0 0.85

Sugarbeetbeetsugar

0 .6 -1 .0 0 .7 - 1.1

Sugarcane 0.75 0 .5 0.1 1.2

Sunflower 0.25 0 .5 1.0 0.95

Tobacco 0.2 1.0 0. 5 0 .9

Tomato 0.4 1.1 0.8 0.-, 1.05

Water melon 0.45 0.7 0.8 0.8 0.3 1.1

Wheatwinterspring

0.20.2

I 0.61 0.65

0 .50.55 i . l j

possible when the likely yield losses arise from differences in the kv of individual growth periods.

Tlie yield response to water deficit of different crops is of major importance in production planning. For example, under conditions of limited water supply and with water deficit equally spread over the total growing season, the y ie ld decrease for maize (total growing period ky - 1 -25) w ill be greater than for sorghum (ky - 0 .9 ).Consequently, when such crops are grown within the same project area and maximum production per unit volume of water is being aimed at, maize would have the prior ity for water supply. Also when maximum total production for the project area is being aimed at, and land is not a restricting factor, the available water supply would be directed toward fully meeting the water requirements of maize over a restricted area; for sorghum, the overall production will increase by extending the area under irrigation without fully meeting water requirements provided water deficits do not exceed certain cr itica l values.

Similarly, the yield response to water deficit in different individual growth periods is of major importance in the scheduling of available but limited supply in order to obtain high est yield. In general, crops are more sensitive to water deficit during emergence, flowering and early yield formation than they are during early (vegetative, after establishment) and late growth periods (ripening). This implies that timing of water supply IS as crucial as the supply level over the total growing period. Planning of seasonal supply must therefore take into consideration the optimum allocailon of water supply to the crop over the growing season. In terms of water management this would mean that water allocations of a controlled but limned supply would be directed toward meeting the full water requirements of the crop during the most sensitive growth periods for water deficit rather than spreading the available limited supply to the crop equally over the total growing period. For example, for maize, the supply would be directed particularly to the flowering and yield formation periods. It follows that where crops are grown under supplemental irrigation the water application must be programmed so that •ufficient water is available in the soil during flowering and yield formation,

EX AM PLE :

Glvyn : Maize with total growing period 1 May to August (123 days)

May lune lulv Aufl Totalgrowth period (day) establ (25) veg (30) flow (30) yield form (38) (123)

90 192 285 273 8^0

( i ) Water supply is 1(3% (85 mm) less than total water requirements (840 mm) with deficit equally spread over the total growing period (123 days)I - ETa/ETm 1-755/84.0 calc 0.11 . Ya/Ym 1 .2 5 x 0 .1 Table 24 0.125 Ya/Ym - 8 7 . ^

( i i ) Water supply during July is 30% (85 mm) less than water requirements of (hat month (flowering period 2, 285 mm)1 - ETa/ETm 1-200/285 calc 0.31 - Ya/Ym 1.5 x 0 .3 Table 24 0.45 Ya/Ym - 5 $

( h i ) Water supply ts 10% (8^ mm) less than total water requirements (840 mm) with deficit occurring in the flowering period (July) only 1 - ETa/ETm 1-755/840 calc 0.1’ at flowering Fig. 20 0.45-0*65 Ya/Ym ■ 5 ^

uiaiioi. examples of yield response to alternative water supply schedules • r « also given in detail m Chapter VI.

40

VI. APPLICATION IN PLANNING. DESIGN AND QPERATIQM OF IRRIGATION PR01ECTS

In the planning, design and operation ot irrigation projects, the production objectives must be related to the physical resource Base, particularly climate, toil and water supply, in order to ensure that production proposed and yields predicted can be achieved and maintained. A lso, several technical, economic and organizational factors must be considered to arrive at a technically sound, managenally workable, economically and financially viable project which is at the same time in accordance with the development and production objectives.

An important element in the evaluation of crop production under irrigation is the available and required water supply over lime and acreage. When available water supply is adequate and fully meets crop water requirements, the production is maximum and tne required supply depends on the crop selected, the length of the growing season and the irrigated acreage. When available water supply is limited, production is determined by the extent to which full water requirements can be met by the available water supply over the total growing season.

The cropping patterns of the project (e .g . crops, crop rotation, crop intensity) and the efficiency with which production resources can be u s^ are essential input considerations in the overall project planning. Selection of cropping patterns must carefully consider the climatic, soil and water requirements of crops. The length of the growing season and the climatic conditions within the growing season dictate the type of crops and the cropping pattern that can be considered. These must also match the available soil and water resources. The climatic and soil requirements and growing periods of crops are presented in Table 2.

For crops that are climatically suitable, their water requirements must be considered in relation to both water supply and the efficiency of water utilization in crop production (Ey). When water supply is adequate and full water requirements of the selected crops can be met, crop selection, total acreage and total production are primarily determined by factors other than water. When water supply is limited, crop selection, total acreage and total production are primarily determined by the extent to which the available water supply over the growing season can meet full water requirements of the crops, and the highest water utilization efficiency that can be obtained from the available water supply. Water utilization efficiency (Ey) of crops is presented in Table 2.

Decisions on the m ost su i t ab l e crop calendar must be made at an early stage of the project planning and design to attain the most efficient use of the available water supply and an adequate supply and distribution system. For project operation, the most suitable crop calendar must be clearly outlined well before the start of the growing season. Depending also on the available supply, an evaluation and first determination of the water supply schedules can be made. To achieve a high water use efficicocy and a high production, the water supply schedules must be adjusted according to the changes in crop water requirements over the growing period. To cater particularly for periods of water shortage, continuous updating of the schedules Is required.

Step by step calculation procedures are presented on crop selection, crop acreages, and water use and scheduling of available water supply in relation to crop production. Two main conditions are distinguished:

1. Adequate water supply condition when the available watermeets full crop water requirements ( i . e . ETa - ETm and Ya - Ym if other inputs do not limit yields). Here the role

42

of management 15 directed toward manipulating water and other inputs to attain maximum production per unit of land for the selected crops over the available acreage.

2. Limited water supply condition when available water eithermeets full crop water requirements over a restricted acreage ( i . e . ETa - ETm and Ya - Ym) or partially meets crop water requirements over an extended acreage ( i . e . E Ta< ETm and Ya< Ym with other factors adequate). Here the role of management is directed toward manipulating water and other inputs to attain maximum production per unit of water for the selected crops and acreages.

These calculations constitute an essential input in the evaluation of crop production for a given irrigation project. In addition to water, other variables such as farmers' preference, availability of labour and farm machinery, market and profits, must be considered in determining optimum production. Presentation of optimization models that take such factors into account is outside the scope of this publication.

1. ADEQUATE WATER SUPPLY

When the available water supply fully meets crop water requirements, crop selection and crop acreage are primarily determined by factors other than water availability and water use, although the capacity and cost of the irrigation supply and distribution system do have an influence. To plan, design and operate the water supply and distribution system for the project in relation to water available and water requirements, the procedure must consider: ( 1) selection of crops and cropping pattern; ( i i ) monthly ( o r ten-day) and peak supply requirements; and ( i i i ) schedule of irrigation water supply over the growing season.

1. 1 Selection of Crops and Cropping Patterns

When water supply is adequate, crops and cropping patterns that con be considered suitable will be those whose climatic requirements are met by the prevailing climatic conditions and the length of the growing season (Table 2). When data on crop yields are not available for the given location, a first estimate can be made with the help of Table I or can be calculated by the vield prediction methods given in Chapter I. Similarly, an estimate of yield per unit of water (Ey) for the climatically suitable crops can be obtained (Table 2) to indicate the crop water requirements per unit of produce.


a. Determine cllmattcally suitable cropsCollect available clitnatic data; evaluate climatic conditions in relation to crop requirements; select crops that are most suitable for the given climate and soil.Determine cropping patternsDetermine most likely length of grow in g periods of the selected crops in relation to the total growing season and time required for other farming operations.

Select optimum cropping pattern in relation to yieldDetermine for alcemactve crops and cropping patterns the yieldas determined by climate and select optimum cropping pattern andpossible vneld s ,

43

EXAM PLE :

]an

Tmean URHmcan % 65n hour/day 7,4 Rs mm/day 4.9

Feb M ar Apr

15 17.5 2165 63 508.0 8.9 9.76.4 8.5 9.-8

May June July Aug Sept Ocl Nov Dec

25.5 27.5 28.5 26.5 26 24 20 15 .545 50 55 57 60 64 68 68

10.8 11.4 1 1 .5 n . i 10.4 9.6 8.6 7.510.8 11.3 11.3 10.4 9-1 7 .1 5.4 4.5growing season

Calculation;

Climaiically suitable selected crops (Table 2):

May - August April - October/November May - August May - October November - Apn l November - Apn l November - April

Possib le cropping patterns;

wheat/maize/bean/maize or sorghum wheat/maize/bean/groundnut wheat/cotton/bean/moizc or sorghum

For selecting the optimum cropping pattern maximum harvested yield (Ym) and water utilization efficiency (Ey ) should be taken into account in addition to other cr iter ia ;

(Tables 1 and 2)

maize 24 - 28®C 120 dayscotton 25 - 30 180sorghum 25 - 30 120groundnut 26 - 30 120wheat 18 - 22 150bean 15 - 20 120onion 15 - 20 120

Ym ton/ha

maize (grain) 7-9 0 . 8- 1.6cotton (seed) 3-4,5 0 .4 -0 .6sorghum (grain) 3. 5-5.0 0 . 6- 1.0groundnut (unshelled) 3 .5 -4 .5 0 . 6-0.8'vheat (grain) 4-6 0 . 8- 1.0bean dry 1 . 5- 2.5 0 . 3 -0.6

fresh 6-8 1 , 5-2.0onion bulb 35-45 8-10

1.2 Monthly (or ten-day) and Peak Supply Requirements

The main variables in determining the monthly (or ten-day) and peak supply requirements are: the water requirements of the crops, the crop acreages, the efficiency of the supply and distribution system, and the leaching requirements. To minimize the design capacity of the system, adjustments in the crop calendar and crop practices may be required. These may vary from making optimum use of seasonal rainfall and water stored in the soil from pre-season rainfall to reducing peak supply requirements by shifting sowing dates so that different crops do not reach peak water requirements at the same time.


Crop water requirements (ETm)Calculate reference crop evapotranspiration (E T o ) on a laonthly or ten-day basis; select appropriate crop coefficient (kc): calculate crop water requirements (ETm • kc . ETo) in mra/perlod

44

b. Net irrigation requirements (In)Determine effective rainfall (P e ) and groundwater contribution (Ge) to crop va ter requirements in mm/period, and actual depth of available soil water over the root depth at start of the growing period (Wb) in mm; calculate In - ETm - (P e + Ge + Wb) in mm/period,

c. Irrigation supply requirements (V )Determine leaching requirements (L R ) and conveyance (Ec), field canal (Eb) and field application efficiency (Ea) or project efficiency (Ep * Ec . Eb , Ea) as fraction; calculate foracreage (A ) ;

^ - '" ’ /period

EXAMPLEGiven; Location 3 0 ^ ; altitude 95 <n; crop is grain maize, with growing penod 1 May to 31 August; initial stage is 20 days; crop development stage is 33 days; mid-season stage is 40 days; and late season stage is 28 days.

ETo, mm/day kc, fraction ETm, mm/day

mm/month Pe , mm/month Ge, mm/month Wb, mmLeaching requirement (LR ) is 0.44 of total supply requirements; project effi c I on c V ( E p ) i . L ; fi old application effi n p--- ~ v (Fn') i 0

Calculation:

Assume leaching to take place after growing season:

May June July Aug Total

6.9 9.4 8.0 7.6 e x ,11. 10.4 0.75 1.15 0.85 e x . I I .23.6 7.1 10.1 6.5 e x .11.3110 212 314 201 840

20 - - - 20

In , mm/month V , m^/ha/month

at field inlet

90 212 314 201 020

1265 3030 4485 2070 11670at head work 2250 5300 7050 5025 20425

VpeakmV ha/month

V 1 r 0b i:- !c I.'T 1 boT al growing period7850

36500

1.3 Schedule for lrt iki.uUwj:. a j i c r bupply over the Growing Season

For high crop production, the design and operation of the supply and distribution aystem of the project must lie geared toward delivering water to the fields at the pre-dctermined interval and depth of irrigation, which meets the changing water mquircfnents of the crops over the growing season. The supply schedule withm the supply and distribution system must be based on the supply requirements of the lowest irrigation unit or the individual field. The supply requirements at the field level are expressed in irrigation interval ( i ) fn days and m net irrigation depth (d) in mm- The main variables in determining i and d when ETa “ ETm are water requirements (ETm), root depth CD), water holding capacity of the soil (Sa) and level of available

4 5

soil water depletion (p ). To a r r iv e at the supply schedule within the supply and distribution system o f the p ro jec t, expressed in flow rate (m*/sec) and now duration (hours ), the supply requirements o f the Individual fie lds are weighted and subsequently determined for a block of fie lds and for areas served by mam canals, taking into account the irr igation e ff ic iency and leaching requirements.

C A LC U LA T IO N P R O l LULRE

a. Soil water balance (W e)Determine for monthly (o r shorter) periods the soil water balance or actual depth o f available soil water o ver the root depth at the end of a month (o r period thereof) We « P e + Gc + Wb - ETm in mm, and plot ( s e e example line 1); note that We at the end o f each month IS equal to Wb at the botjHininc of iho next month -

b. Total available soil water o ver root depth (S a .D )Determine total available soil water (S a ) in mm/m;determine for given crop root depth (D ) in m fo r eachmonth (o r period thereoO; calculate Sa.D in mm for each month (o r period ihereoQ, and plot (line 2).

c. Remaining available soil water o ver root depth whenE T a < ETm | ( l-p )S a .D lDetermine for given crop and ETm the fraction (p ) of the total available soil water when ETa ■ ETm (Tab le 20); calculate ( l - p )S a .D in mm for each month (o r period thereoO, and plot Gme 3).

d. Interval and depth of irr igation application (i and d)Apply graphical method; when soil water balance (line 1) TT^ets maximum soil water depletion o ve r which ETa • ETm, o r ( l - p )S a .D (line 3), replenish soil water with water depth equal to p. Sa.D in mm, and plot (line 4 ); plot new soil water balance curve Gme 5) para lle l to the old one (line 1) until ( l - p )S a .D (line 3 ): repea l; read approximate date, interval ( i ) in days and net depth (d) in mm; note that tomake maximum use of available soil water, step d can alsobe started at the time o f harvest with depth o f available soil water at time o f harvest equal lo (1 -p )Sa .D .

e . Operation o f supply and distribution system Determine duration (hours) and interval (days) ; oi l supply; quantify supply schedules for different crops and acreages over the growing season for selected method o f d e liv e ry . (F o r details see FAO Irrigation and Drainage Paper No. 24, 1977, revised vers ion , Pa r t II, Chapter 2 . )

In the following example, it is assumed that the irrigation supply is fully controlled and the interval and depth of irr igation application can be chosen to maintain ETa - ETm and Ya - Ym.

46

E X AM PLEG w en : Crop \s maize; soil is medium textured with total available soil water (S a ) 140 mm/m; climatic and crop data are :

May

3.611020

June

7.1212

July

10.1 314

Aug

6.5

Total

201

1.2

640ETm, mm/day ETm, mm/month P e , mm/monthGe, mm/month - - -Wb, mm 7 0 (p r c - im g . )D, m 0 .5 1.0 1.2Water supply is adequate and can be fully controlled; application efficiency (Ea) is 0. 7.

Calculation:

ex.11.3

W e- Pe + G e> W b - ETm mm/month

Sa.D , mm fraction

l - p )S a .D , mm apply plottingprocedure number of irrigations approximate date

I

-20 -232 -546 -747 line (1)

70 140 170 170 line (2)0.75 0.5 0.4 0.55 Table 20

18 70 102 77 line (3)

(pre)+2 4 4 1(2)* Fig. 4(1/5) 5/6 6/7 11/8 Fig. 417/5 12/6 12/7 (27/8)*2 B Ij 20/6 19/7

28/6 28/715 8 7 15 Fig . 4

(70)+55 60 70 95 Fig . 4( 100)+80 05 100 135 calc

1 , days d , mmirrigation depth (g ross )

• last irrigation falls shortly before harvest and can be omitted or scheduled ea r l ie r with a reduced depth.

Similar calculations can be made for different crops grown simultaneously in the project area. To a rr ive at an irrigation supply in terms of flow rate (m^/sec) and flow duration (hours), the irrigation interval ( i ) and depth of irrigation (d) are weighted for different crops according to their respective field acreages, blocks of fie lds, acreages served by laterals and mam canals, taking into account irrigation effic iency and leaching requirements.

However, to simplify the operation of the supply system, in many irrigation projects fixed irrigation intervals and/or fixed depth or irrigation application are used Since crop water requirements change over the growing period, the use of fixed interval* and/or fixed depths of irrigation causes either over- or under-irrtgation during the different parts of the growing period. This in turn leads to inefficient use of water or causes reduction In crop y ie ld s , as shown In the following examples

EXAM PLE

lyg i: Previous example ©n maize; a fixed irrigation interval (O of day* I* u*cd.

47

\

Fig. L

Calculation: Tha 15 day interval is correct for May and August; duringJune and July the 15 day interval leads to crop^ water defic it. In July :ETm - 10.1 mm/day, Sa - 140 mm/m, D - 1.2 m, p - 0 .4 ,

140 X 1,2 calcat ETm - 10.1 Table 20(8.1 W . 5 + 9.1 ♦ 8.7)/4 Table 211 - 8.4/10.1 calcat flowering Table 241 .5 x 0 .1 7 calc

Sa.D , mm p, fraction ETa, 1 - 1 5 days 1 - ETa/ETm ky maize 1 - Ya/YmYield decrease due to water deficit in July

170 mm 0.48.4 mm/day 0.171.5 0.25 23

2. LIMITED WATFP ^VPPLY

4 8

When w ater supply is l imited, considerat ions on crop se lect ion and acreage i r r iga ted should be b a s ^ on crop y ie lds as affected by the extent to which crop water requirements (E T m ) a re met by the ava i lab le water supply o v e r the grow ing season.A f irs t evaluation can be made by consider ing the ef fect o f limited seasonal supply on crop y ie lds and total production. H ow eve r , fo r a full evaluation o f the e f fect o f limited water supply on y ie ld and production, considerat ion must be given to the e f fec t o f the limited water supply during the individual growth per iods o f the c rops . W here crops under consideration a re v e ry sensit ive to water supply d e f i c i t s , scheduling o f the supply IS based on meeting full crop water requirements. Where crops under cons id eration a re less sensit ive to water de f ic i t and can be grown with acceptable y ie ld s but without meeting full water requirements, scheduling o f the supply is based on minimizing water de f ic i ts in the most sensit ive growth pe r iods . During per iods o f unpredictable water shortages , within season adjustments o f water scheduling must be made in relation to the d i f fe rence in the yield response to water de f ic i ts on the crops and their individual growth pe r iods . Th is applies both to control led and uncontrolled water supply at headworks .

To plan, design and operate the water supply and distribution system fo r the pro jec t in relation to production leve l and water requirements, the procedure must consider ( i ) se lection o f crop and cropping patterns; ( i i ) seasonal and monthly water supply requirements and crop production (y ie ld pe r unit area and total p ro jec t production); and ( l i t ) schedule o f i r r iga t ion water supply o v e r the growing season.

Selecuou oi and k,roppiaiz Pat iorns

When water supply is limited, crops and cropping patterns that can be considered suitable w il l be those whose climatic requirements a re met by the preva i l ing climatic conditions and the length o f the growing season (Tab le 2). When data on crop y ie ld under adequate water supply a re not ava i lab le fo r the given locat ion, an estimate can be made with the help o f Table 1, o r can be calculated by the y ie ld pred ict ion methods given in Chapter I. In addit ion, selection o f crops and their acreages must consider the crops that a re most e f f ic ient in water utilization (a high Ey) under adequate water supply, as well as ihose which a re able to maintain an acceptable yiehi level under limited water supply (a low ky).

r i ' l ATION PR O C E D U R E

Determine cUmaucally suitable cropsCol lec t ava i lab le climatic data; evaluate climatic conditions in relation to crop requirements ; se lec t c r o p s that a re most suitable fo r the ^ v e n climate and so i l .

b. Determine crops and crop acreages in re lat ion to water supply1 valuate fo r the c l imatical ly suitable crops the ava i lab le water

in relation to water requirements, water util ization ency (E y ) and yield response factor (ky ) .

s im p lye f i ic ie i

Saleci optimum cropping patternDetermine fo r crops with high Ey and high ky values the crop rotation and crop acreages where full water requirements are met by avai lab le water supply.Determine for crops with high Ey values and low ky values the crop rotation and crop acreages where water requirements a re partially met by avai lable water supply.

For the example, step (a) follows the analysis made under Chapter V I . ' . ’ . Steps (b) and (c ) are discussed jointly in relation to seasonal and periodic water supply and production level, Chnpter VI-3. 1 and 2.

2.2 Seasonal Supply

Under limited water supply, a first evaluation of actual crop j ; anJtotal production (P ) for the project area can be made by considering the yield response factor CKy) fo r the ,total growing period of the crops with high Hy values in relation to the ratio available seasonal and required seasonal supply. Since ky is used together with the relative evapotranspiration deficit (1 - ETa/ETm), the available and required supplies need to be expressed m terms of ETa and ETm.

Actual yield (Ya )

The actual y ie ld under limited water supply is obtained by expressing the available and required seasonal water supply in terms of ETa and ETm. Subsequent application of ky for the total growing period provides an estimate of the relative yield decrease (1 - Ya/Ym).


a. Available water supplyFrom hydrological data and irrigated acreage, determine,after correction for irrigation efficiency, the net water supply lo the crop over the total growing period in m^/ha and ETa in mm,

b. Relative evapotranspiration deficit (1 - ETa/ETm)Determine crop water requirements (ETm) in nun for the total growing period and calculate (1 - ETa/ETm).

c. Relative yield (Ya/Ym)Select appropriate yield response factor (ky) for the total growing period (Table 24), calculate (1 - Ya/Ym) “ ky(l - ETa/ETm) and obtain Ya/Ym.

EXAM PLEG iven : Crop is maize; total growing penoU i May to August; crop water requirements (ETm) are SiO mm; effective rainfall is 20 mm; available water supply at headworks is 13 750 m /ha; projectefficiency (Ep) - 0 .4.

Calculation:Available to crop, ETa 0.4 x 13 750/10 ♦ 20 calc • 570 mmETm example • 840 mm1 - ETa/ETm 1 - 570/840 calc - 0.32ky Table 24 - 1.251 - Ya/Ym ky<l - ETa/ETm) calc • 0.40Ya/Ym calc - j g j

49

50

Total production for the oroiect area (P )

To maximize total production under a limited water supply and a given cropping^attem of crops with high Ey values, a first evaluation of the total production CP) for the irrigated acreage can be obtained by considering the crop response factor (Vy) for the total growing period. Total production CP) is defined as actual yield (Ya) over the total irrigated acreage (A ) or P - A .Y a . Based on the ky values, two cases can be distinguished ;

when ky > I ; for maximum total production (P ) , the acreage (A ) is based on available water supply meeting full crop water requirements or ETa - ETm; Ya - Ym over the acreage (Am) where Am is defined as the irrigated acreage with crop water requirements fully met.

when ky < 1; for maximum total production (P ) , the acreage (A ) is based on available water supply partially meeting the crop water requirements or ETa < ETm, and Ya< Ym but Aa >Am, where Aa is defined as the irrigated acreage with water supply less than the required supply to meet full crop water requirements.

The effect of limited warer supply per unit area and the ky factor of the total growing period on total production CP) is shown in Table 25- Pm represents the totalF reduction from acreage Am with crop water requirements fully met by available supply

ETa - ETm, Ya - Ym and Pm - Am.Ym); Pa represents the total production from the acreage Aa with crop water requirements partially met by the available water supply and 'savings' in water supply are used to extend the irrigated acreage Am (ETa < ETm, Ya < Ym, but Aa > Am and Pa - Aa. Ya).

Table 25 Relative Total Production (Pa/Pm) for DifferentValues of ETa/ETm and ky factors for the Total

Growing Period

ETa/ETm0.6 0.7 0,8 0.9 . U ) _

0.6 1.27 1.17 1.10 1.04 1.00.8 1.13 1.08 1.05 1.02 1.01.0 1.0 1.0 1.0 1.0 1.01.2 0.87* 0.91* 0.95* 0.98* 1.0*1.4 0.73* 0.83* 0.90* 0.95* 1.0*


b.

Available water supplyFrom hydrological data, and after correction for Irrigation effi ciency, determine for the total growing period the water supply available to the crop in m3; for different irrigated acreages determine water supply available to the crop in m /ha,

Relative evapotranspiration (ETa/ETm)Determine for the total growing period the crop water requirements (E Tn ) in nun and calculate ETa/ETm.

c . Relative total production (Pa/Pm )Select yield response factor ky for the total growing period and determine for different values of ETa/ETm the relative total production CPa/Pm) from Tab le 2S-

E X A M P L EG iven : Crop is maize; grow ing period Is 1 M ay to 31 Auguat; watersupply is ICXXlOOOm ; project efficiency (E p ) la 0 .4 .

Calcu lation :

Availab le to crop kyETm y mm a rea , haaverage supply, m^ha E T a , mm ETa/ETm kyYa/Ym Pa/Pm

0 .4 X 1 000000 calc 400000

40 47.6 50 60 70

Table 24 • e x .11.3 - assume

1.25 640 mm

10000 8400 8(XX) 6650 5 700 calc840 840 800 665 570 calc

(1 .0 ) 1.0 0.95 0 .8 0.68 calc1,25 1.25 1.25 1.25 1.25 given

(1 ) 1.0 0.94 0.75 0 .6 calc(0 .84 ) 1.0 0.90 0.94 0.89 Table 25

2.3 Schedule of W ater Supply

A full evaluation of crop yield response to limited water supply can only be mode by considering the distribution of available water supply over the individual crop growth periods. Under conditions of limited water supply, the supply schedule should be directed towards minimizing water deficits during the most sensitive periods (o r when ky for the individual growth period is high). This applies for most crops during the flowering and yield formation per iods . In scheduling limited water sifoply two main conditions con be distinguished;

( i ) ava ilrb le supply is fully controlled at headworks (v iz . supply from a r e s e rv o ir )

( i i ) available supply at headworks is uncontrolled and v a n e s with time (v iz . available discharge of a r iv e r ) .

( i ) Fully Controlled but Limited bupplv

\When water supply is fully controlled, the irrigated acreage is mainly determined by the total available water supply and the required supply to attain the expected level of crop yield. Supply scheduling is directed toward minimizir.g water deficits during the individual growth periods with high ky values.

C A L C U L A T IO N PR O C ED U R E

Crop water requirements (ETm )Determine for monthly (o r ten-day) periods and for eavi. crop growth period the maximum evapotranspiration (ETm ) in mm.

Yield response to water supply (Ya/Ym and ETa)Determine for the individual growth periods the respective ky value; select relative yield level (Ya/Ym) and determine corresponding actual evapotranspiration (ETa> in m n .

52

c. Irrigation scheduleSelect for the individual growth periods the level of actual evapotranspiration (ETa) in mm/period, available soil water over root depth (Sa .D ) in mm and fraction of soil water depletion (p) when ETa - ETm; calculate irrigation interval (0 in days and depth (d) in mm.

d. Irrigated acreageFrom hydrological data determine for the individual growth periods total available water supply in m ; calculate acreage m ha from available and required supply (V ) in m^/ha.

e. Operation of supply systemDetermine duration (in hours) and interval (in days) of field supply, and quantify supply schedules for blocks of fields, and for acreages served by laterals and mam canals.

EXAMPLEGiven: Crop is maize; growing period 1 May to 31 August with an establishment period of 25 days, a vegetative period of 30 days, a flowering period of 30 days and a yield formation period of 38 days. Monthly maximum evapotranspiration CETm) IS, for May 3.6, for June 7*1, for July 10.1 and for A u ^s t 6. 5 mm/day; soil is m^ium textured and total available soil water ( S ^ IS 140 mm/m; root depth during the establishment period is 0 . 5 m , during the vegetative period 1.0 m, during flowering and yield formation,1.2 m. Available water supply is 1000 000 m ; project efficiency (Ep) is0.4. Assume maximum irrigated acreage with yield per ha equal to 80% of the maximum.

(0) (1) (2) (3)esta- vege flow yield TotalblisKm, tative ering form.

ETm, mm/day calc 3.6 6.4 9.5 7.2ETm, mm/penod calc 90 192 285 273 840ky Table 24 0.4 0.4 1.5 0.5water savings X X

0.8ky (period 1 & 3)V X X(1 - Ya/Ym) given 0.2(1 - ETa/ETm) calc 0 0.25 0.25ETa/ETm calc 1 0.75

2850.75

ETa, mm/penod calc 90 144 205 724ETa, mm/day calc 3.6 4.8 9.5 5.4S a .D , mm/rootzone calc 70 140 170 170p, fraction Table 20 0,75 0.5 0.4 0.55i , day* Table 21 15 26 7 28d , mm (i X ET a) calc (pre 70)

5555

125 6565656565

150* 630

Date calc (pre 1/5) 15/5 30/5

26/6 3/710/717/724/731/7

28/8*

Fsnmatad value^or the combined effect of water deficit in periods 14 3.

Irrigated acreage:- 0.4 x 1000000/6 300 - 63 ha,

* Last irrigation falls shortly before harvest and can be omitted (o r scheduled ear lie r with reduced depth).

When rainfall occurs, the irrigation interval can be extended with a number o f days equal to Pc/ETa, where Pe is the effective rninfnU in mm occurring during that irrigation interval.

0 0 Oncontrolled and L,injited Supply

When water supply is uncontrolled, irrigated acreages are mainly determined by the available supply during the different growth periods, the effect of water dcflcita on yield during those periods and the s e le c t^ yield level. Crop selection and crop calendar should, when possible, be adjusted so that periods with high ky values do not coincide with periods of limited water supply.

53


a. Crop water requirements (ETm)Determine for monthly (or ten-day) periods and for the individual growth periods the maximum evapotranspiration ( ETm) in mm.

b. Yield response to water supply (Ya/Ym and ETa)Determine for the individual growth periods the effect of evapotranspiration deficit on crop yield (ky); select relative yield level (Ya/Ym); by comparing available water (E Ta ) with crop water requirements (ETm), determine the critical growth period for water deficit; determine acreage in ha from available and required supply for the critical growth period; check for other growth periods if water supply IS adequate; if not, adjust acreage to attain selected yield leve l (Ya/Ym).

Irrigation schedule (i and d)Select level of mean actual evapotranspiration (E Ta ) in mm/day, available soil water (Sa ) in mm/m over root depth (D) in m, and level of soil water depletion (p) in fraction when ETa - ETm; calculate irrigation interval ( i ) in days and depth (d) in mm.

d. Operation of supply systemDetermine duration in hours and interval in days of field supply, and quantify supply schedules for blocks of fields, and for acreages served by laterals and main canals.

54

EX AM PLE

G i T « : Crop is maize; growing penod 1 May to 31 August, with an establishment penod of 25 days, a vegetative period of 30 days, a flowering penod of 30 days and a yield formation period of 38 days. Monthly maximum evapotranspiration (ETm) for May is 3 .5 mm/day, for June 7- 1, for July 10.1 and for August 6. 5* Soil is medium texture and total available soil water (S a ) 1 s 140 mm/m; root depth CD) during the establishment period is 0. 5 ni, dunng the vegetative penod 1.0 m and during flowering and yield formation 1.2 m. Water supply is 161 000 m in May, 261 000 m m June, 269000 in July and 309000 m August. Assume maximum inmgated acreage with yield per ha equal to 70% of the maximum.Calculation:

length of period (days) ETm, mm/period ETm , mm/dav

givencalccalcTable 24

(0)esta-bltshm.

2590

3.60.4

(1)vegetative

301926.40.4

(2)flowering

302859.51.5

(3)yieldform.

382737.20 .5

total

123840

ETa • 0 .9 ETm mm/period calc 81 173 257 246Ya/Ym for ETa/ETm - 0 . 9(%) calc 96 96 85 95ETa - 0.8 ETm mm/period calc 72 154 228 218Ya/Ym for ETa/ETm - 0.8(%) calc 92 92 70* 90ETa - 0.7 ETm mm/penod calc 63 134 200 191Ya/Ym for ETA/ETm - 0 . 7(%) calc 88 88 55 85ETa - 0 .6 ETm mm/pcnod calc 54 115 171 164Ya/Ym for ETA/ETM - 0.6(%) calc 84 84 40 80

available water supply inm V period given 130000 240000 260000 370000 1000000

net average supply (Ep * 0 .4 ) calc 52000 96000 104000 148000 400000Ya/Ym % given 70cntical penod X• Irrigated acreage (104 000/2 280) 45-6net available water, m^/ha calc 1140 2105 2280 3245no supply restrictions in growth penod s 0, 1 and 3

ImgApgn achfidulg!ETa/ETm ETa, mm/day ETa, mm/period D. Sa, nun/root depth p , fraction 1 , daya d , mm

approximate date

calc 1.0 1.0 0.8 1.0calc 3.6 6.4 7-6 7.2

90 192 228 273calc 70 140 170 170Table20 0.75 0 .5 0.4 0.55Table 21 15 11 15 13calc (pre 70) 70 115 95

55 70 115 9555

calc (p re 30/4) 11/6 5/7 2/815/530/5

22/6 20/7 15/8

3 . A D D IT IO N A L R E L A T E D A P P L IC A T IO N S

3' 1 Prior ity of Water Supply Amongst Cropi Dunna Periods of Wgter fihortaoea

In the operation of the supply and distribution system, decisions must be made on the best allocation of available water at the lime of water shortage. During the individual growth periods, crops vary in their yield response to water deficits* To minimize yield reduction, the irrigation supply should be directed toward minimizing water deficits during the growth periods with high ky values.

When water supply is short, the ky values of the growth periods for crops grown simultaneously in the project area indicate the priority in water supply allocation. This priority can be expressed in terms of yield response to the level of water supply. Detailed calculations are given under V I . 2.

EXAMPLEGiven: Start of the growing season is May; crops are maize, cotton and sunflower; water shortage occurs during July and August; attainment of maximum production per unit area is pursued.

Calculation:From information for the different crops given in Part B:

May June July August Sept.

growth periods:maize establ. veg. flow. yield form.cotton establ. veg. flow. flowering yield form.sunflower establ. veg. veg. flowering yield form.

ky:maize 0.4 0.4 1,5 0.5cotton 0,2 0,2 0,5 0.5 0.5sunflower 0.25 0.25 0.5 1.0 0.8

Supnlv Diioritv:

Oct.

npening

0.25

July:August

1 maize, 2 and 3 cotton and sunflower 1 sunflower, 2 and 3 maize and cotton

3.2 Rehabilitation of i r o io ^ ts through Improved Operation of WgicrK .en am ii ia i ion oi tSupply and Distribution Systems"

For high yields, the operation of the water supply and distribution system must be directed toward meeting the crop water requirements over time and acreage. In some projects, supply schedules are based on a fixed interval and/or a fixed depth of water application, regardless of the changes in crop water requirements over the growing period. However, field data, reflecting y ie ld losses due to excessive or inadequate water supply to the crop, are in many cases scarce or not available. In exisiDig projects, the lack of this information often inhibits the required unprovemeni programmes.

Improvement of existing projects calls for reliable data at the ferm Level on crop water requirements and irrigation supply scheduling m relation to crop yields. Based on these data, criteria for optimum woter use at the farm level can be developed,

in turn can form the basis for determining the measures needed to improve the physical and managerial operations of the water supply system.

The likely benefits of improvement of the water supply system in existing projects be obtained from an analysis of the present yield level compared to the maximum yield attainable under a high level of water management. To measure the effect o f present water supply on present y ie lds, an analysis is required on interval and depth of water application to the field over the growing season.

A fter first calculating maximum evapotranspiration (ETm) (Chapter 11), the actual evapotranspiration (E Ta ) under the present water supply can be obta in^ (Chapter III). Subsequently, the relative evapotranspiration deficit (1 - ETa/ETm) for each crop growth period after first calculating maximum yield (Ym) (Chapter 1) and, by applying the crop response factors (ky)» the effect o f water deficit on present re lative yield can be obtained by (1 - Ya/Ym )- k y ( l - ETa/ETm).

Calculations similar to those given in Chapter VI. 2 can be applied to calculate, fo r the present available water supply, the yield level that can be obtained under improved irrigation supply scheduling. The present and improved yields are also suDject to factors other than water. However, an indication of the expected yield increase due to improved water supply and management is obtained by following the presented methodology.

56

3*3 Reservo ir Operation

In planning and design of water supply systems fed by rese rvo irs , the water re lease for irrigation is sometimes based on selected water duties or supply norms.The required supply for irrigation is then considered as an operational parameter, rather than an operational variable; the re lease then represents, for a given irrigated acreage, a fixed flow of water over a fixed, often calendar-based, time period. While the concepts of water duty and supply norms are helpful at the planning stage, considerations in relation to efficiency of water use and leve l of crop production greatly assist in the most effective operation of re servo ir re leases.

Reservo ir operation over the growing season should be directed toward minimizing water shortages during these crop growth periods when crop yield response to water deficits is most sensitive. The calculations involved are ( i ) determination of available supply over the growing season; ( i i ) determination of crop water requ irements (ETm) for the different crops for ten-day periods; ( i i i ) selection of yield response factors (ky) for different crops and ( iv ) determination of the distribution of available supply over the growing season, based on minimizing crop yield losses due to water defic its . Since several crops may be involved, weighted averages need to be used. Dunng pcnods of water shortages, the priority of supply amongst crops within the project area can subsequently be determined (Chapter V I , 3 .1 ).

3 .4 IrTiAOiiQn Efficiency

Irrigation efficiency is normally expressed in terms of the amount stored in the root zone as a percentage of the total water released at the project headworks. It IS separated into three components: the conveyance efficiency (E c ), the field canal efficiency (Eb) and the held application effic iency (Ea) or project effic iency Ep - Ec . Eb . Ea. Mem factors affecting irrigation efficiency are the size of the project, ike nvmbmr end the type of crops requiring adjustments in supply, the canal seepage, the else of the individual fields, the irrigation methods and practices, and managerial

and ic^ntiiLdi la ^ iU t io lor water control. At the planning stage, irrigation eff iciencv 15 normaUy estimated on the basis of experience. The estimated values can ^ check^ only 3 to 10 years after constFuclion of the pro ject, when operators and farmers have become familiar with the water distribution and application.

Irrvgation eff iciency (Ep) is expressed in terms of water loss Forpractical purposes , it is normally considered as constant over the growing season. However, in most cases eff iciencies will vary over the season. For instance, under conditions of limited water supply to the field and when under-irrigation is practised most water applied to the fields is taken up by the crop and field application efficiency may be near 100 percent rather than the frequently assumed 50 to 70 percent. A lso when water is in short supply, more attention is given to water distribution and scheduling, and project eff iciency is consequently higher. Furthermore, the effect of limited water supply on crop yields varies over the growing season, and consequently the impact of water loss on yield van es over the growing season.

Besides expressing it in terms of water losses (m^/m^), irrtgation eff iciency can also be expressed m terms of yield losses by applying the relationships between water supply and crop yield. Under conditions of adequate supply an increase in irrigation eff iciency will save water. Thus an extension of the irrigated area is possible and the total yield is subsequently increased. Under conditions of limited supply, an increase in irrigation eff ic iency will also save water, making a reduction in water deficits to the crop occurring during different growing periods possible, and yield per unit area is subsequently increased.

Consideration of irrigation eff iciency in relation to yield response to additional water supply assists in the evaluation of the need for improvement of irrigation eff ic iency, as, for instance, the decision on canal lining.

57

EXAM PLEGiven; Previous example (Chapter V I . 2.3 ) where Ya/Ym is 0 .7 ; Ep is 0 .4 , Assume j m increase in Ep from 0.4. to 0 .4 4 ; water supply shortage is experienced during the f lowering period (July).

C a lc u la t io n :

net average water supply oAnnnnduring Howering (July), m»

net supply, mVhaET«/ETm 250'285k y , nowermg Table ^( 1 - Ya/Ym)Ya/YmYield increase due to _

increasing eff iciency (0.82 - 0-7)/0.7

calccalc 2 500 mVhacalc 0.86given 1.5calc 0.18calc 0.82

calc

V l i . A D A P T IV E RESEARCH

Crop production and oplimuin use o f water are determined by the total enviroTiment, and consequently a re location spec if ic . The method presented fo r analysing the relationship between crop y ie ld and water use allows an integration through a y ie ld response factor (ky ) o f a la rge number of complex p rocesses into a aimplc quantitative relationship between re la t ive y ie ld d ecrease (1 - Ya/Ym) and re lative water de fic it (1 - ETa/ETm ). The methc^ as such forms a basis o f rational water management in relation to irr iga ted crop production.

In o rd e r that the method has a wide application, the relationship fo r the d ifferen t crops is ( i ) derived from experimental data o f high producing va r ie t ies obtained under conditions where production inputs other than water arc adequate, and ( i i ) presented on a re la t ive sca le . H ow ever, production conditions during the grow ing p en od are location spec if ic , e . g . water quality, f e r t i l i z e r application, endemic plant d iaeases . A ls o , for many locations y ie ld and water use data on which to base the analysis are often lacking. Thus, ver if ica tion o f the presented method and y ie ld -w a te r use relationship through adaptive research fo r a given production condition is v e ry much warranted for use in planning, design and operation o f existing and new irr iga tion p ro jec ts .

The ob jectives o f the experimental programme should in c lude :

- establishment o f crop growth and y ie ld responses to d ifferent leve ls of water supply o v e r the total growing penod for specific crops

- the evaluation from the developed y ie ld response tunctioas of practica l irr iga tion schedules which w ill guarantee optimal y ie lds per unit o f water and/or per unit o r area .

The adaptive research programme must determine ( i ) the maximum y ie ld (Ym ) under conditions o f full water requirements (ETm ) with other growth factors not limiting y ie lds and ( i i ) the e ffect o f l im i t ^ water (E T a ) on y ie ld (Y a ) fo r the total and individualgrowth per iods . Th is inforn.nTu'''i >x ill .illow 'U'rti.',Trtori o f The re la r ’ orxhir.- jrield and water use (ky ).

It must be emphasized that detailed planning o f the experimental programme, including the number o f treatments and rep lications and the type and number o f ob se rva tions and measurements to be made, is most essentia l. In p ract ice it has often shown that ambitiously devised programmes in the course o f execution experienced great d iff icu lties due to insufficient equipment, funds, labour and supervising pe fsonnel.The experimental programme should th e re fo re , espec ia lly fo r the f irs t y e a r (s ) , be simple, with a limited number o f va r iab les involved, and be based on c le a r ob jectives and proper planning.

The experimental programme must be prob lem -so lv ing oriented. T h e re fo re , first of a l l , an analysis must be made of the present y ie lds in relation to the agronomic and ir r iga t ion practices m farm ers ' f ie lds in existing p ro jec ts . This would include an analysis o f crop and crop v a r ie t ie s , the present yield le v e ls , the planting dates and growing periods, the crop husbandry practices such as plant population, cultivation mathods, waad contro l, i^ s t and d isease con tro l, and harvesting techniques as well as the fraqaancy and depth of ir r tga iion with special re fe rence to irr iga t ion methods and pracucaS f irr iga t ion efficiency, water quality, depth of groundwater tab le, and soil and ferohty factors. Such an analysis is nc^cd to determine poss ib le limiting factors to high pronuctior ant! Thnr cffocT*. riiiroved water schedules based on

experimentally determined relationships between yield and water use are amlled in the fie ld . Furthermore, the analysis of present field practices will indicate Uie variables,in addition to water , Ahicb mav to ho irrhiJod m t^o OTtporiinontrtl

59

1. SITE SELECTION

The site selected should be fully representative for the climatic, soil and water conditions of the area where the results will be applied. Areas with steep slopes or low-lying areas subjectcxl to flooding should be excluded. The soil should preferably be deep, without hard pans or dense layers with no physical or chemical limitations, and a high water table should be avoided except where such limitations form a part of the experimental treatment. A drainage system should be included whenever necessary.

The experimental area must be placed within an agricultural area surrounded by irrigated crops. The surrounding area must be Large enough to avoid the so-called 'clothesline* effect (at least 100 x IcS m). A fully controlled and guaranteed water supply should be a v a i l a b l e .

2. IRRIGATION TREATMENTS

Experiments should be conducted with high-producing varieties well adapted to the prevailing climatic conditions, with an adequate plant population, soil fertility and crop protection. To obtain results that are statistically meaningful, each treatment should have sufficient replications.

Water supply schedules should be related to water requirements taking into account climatic and soil conditions, and crop development. Consequently, the interval and the depth of irrigation should vary accordingly over the growing penod. Results have little meaning when fixed irrigation timing is used and only the depth of application is varied according t- fractions o f a reference le ve l , e. g. 1. 1 , 0 . 9 and 0 . 7 times pan evaporation. Irrigation depth per application should preferably be sufficient to bnng the soil water content to field capacity over the effective rooting depth, with additional water applied when leaching o f salt is required.

In order to determine the frequency and depth of irrigatio" for .'ich •rt'.’i*'-.'- », a preliminary supply schedule can be obtained by calculating;

maximum evapotranspiration (ETm) and actual evapotranspiration (ETa) by the methods provided in Chapters 11 and 111

total available soil water oyer the root depth (Sa), using meaaured data on soil water content at field capaci^ (S fc ) and wilting point (Sw), and root depth CD)depletion level of total available soil water (p) for each treatment by information provided in Chapter 111.

Supply schedules will need to be adjusted throughout the course ot the experiment, also taking into account climatic conditions and rate of crop development. The supply schedule should be made possible by the irrigation method used, e .g . small depth of irrigation under surface irrigation methods.

The recommended irrigation treatments a rc :

<i) One *‘wet ireatment" o r treatment with no water defic it o v e r the total orowin^ p en od f^ETa ■ ETm. Ya - Ym)

Experimental resu lts obtained under this treatment w il l p rov ide an indication o f the accuracy o f methods to pred ict crop water requirements (ETm ) and the maximum y ie ld (Ym ) fo r the given crop va r ie ty and grow ing conditions.

Timing and depth o f application is based on the calculated maximum evapotranspiration (F T m ), the total availab le so il w ater (S a ) , the root depth (D ) and the water depletion leve l (p ).Soil water measurements to check the rate o f water uptake from the soil as recorded in the soil water balance sheet a re made frequently o v e r the root depth. For a measure o f soil water status tensiometers and gypsum blocks are needed.Care must be taken that no excess water is lost un-measured through deep perco lation o r la te ra l movement.Regular observation should be made on crop development (s e e check l is t ) ,

( i i ) One "d ry treatment" o r treatment with considerable water de fic it throughout the total growing period ( E T a « ETm. Yd ^ Ym)

Experimental results obtained under this treatment w ill p rov ide the actual yield (Y a ) and actual evapotranspiration (E T a ) under conditions o f water d e f ic it . These results allow a quantification o f the crop response factor (ky) fo r the total growing period when ETa is compared to ETm and Ya is compared to Ym.

The water defic it and consequently the soil water depletion le ve l at which irr iga tion is applied w ill depend on the c rop , soil and leve l o f ETm (Chapter HI). Stunted growth and wilting w ill be observed but serious w ilting fo r a long period must be avoided.Timing and depth o f ir r iga t ion should be based on a continuous measure o f soil water status (so il sampling, gypsum b locks), combined with crop observationse . g . w ilt ing, change o f colour. The selection o f the depletion leve l at which irr iga tion is applied should be based on lite ra tu re re fe ren ces o r Chapter III and actual evapotranspiration (E T a ) should p re fe rab ly be 40 to 50 percent below ETm,

( i l l ) One o r more "m ix ^ treatments" with water defic it during selected individual growth p en od s only (E T a ^ ETm. Ya ^ Ym) ”

Experimental results obtained under this treatment w ill p rov ide the actual yield CYa) and actual evapotranspiration (E T a ) under conditions o f period ic water de f ic its . These results allow a quantification o f the crop response factor (ky ) for the individual growth period (vegeta tion , f low ering , y ie ld formation, npenm g) when for the individual growth periods ETa is compared to ETm and Ya IS compared to Ym.

Depth and interval o f irr igation are based on selected depletion leve ls of available soil water, e.g, fo r most grain crops selected leve ls are 60 , 80 and 1(X) percent o f the total available so il water (S a ) , Treatment combinations are g;ivafi in F igure S. L itera ture re fe ren ces and Chapter 111 can be consulted for Ml«Cttng the depletion leve ls fo r d ifferent crops and growth per iods .Soil water measurements should be made to record the rate o f soil water uptake h y the crops. Regular observations should be made on crop development (see check l is t ) . From water balance sheets, a measure o f ETa can be obtained.The leve l o f soil water depletion (p ) when ETa becomes smaller than ETm can also be determined by plotting ETa against time after ir r iga t ion . In o rd er to make results applicable le other so i ls , the leve l o f soil water depletion (p ) should also p re ferab ly be expressed in soil water tension (b a r ) rather than in volume percentage alone.

60

M

irriQsiion TrMimerM

v«i« SMw v M nip

1 1 I

1 1 < t

1 <1 1

1 < t 4 1

1 < » t 1

1 € 1 4 1

1 < 1

I < ! < 1 < 1

< 1 1 1

<1 1 < 1

<1 < t 1

<1 < 1 4 1

< 1 < 1 1 1

< I C 1 1 < 1

<1

F i g . 5 Poss ib le combinaiion o f irrigation treatments

62

3. EXPERIM ENTAL DESIGN

The experimental design w il l depend on the number o f ir r iga t ion treatments and the number o f va r iab les other than water to be considered. S tatistica l handbooks should be consulted on the most appropriate design , e . g . latin square, sp lit-p lot design . Number o f rep lications fo r each treatment is normally four. During the firs t yea r & simple plot layout with latin square design w\th f o u r water treatments and four rep lications can be used, e . g . fo r maize:

<‘ 1 “ 1

»>2 “ 2 “ 2

'3 “ 3 “ 3 »>3

a. no water de fic it o v e r the total grow ing period

b. w ater depletion to 90% o f the available soil water during the vegeta tive period( 1)

c. water depletion to 90% o f the available soil water during the y ie ld formation (3 ) and npem ng (4 ) periods

d. water depletion to 80% o f the available soil water during the total grow ing period

Latin square design

The number o f water treatments and/or other va r iab les deemed necessary can be increased dunng the subsequent y ea rs . An example is given o f an experimental layout with 12 treatments and 4 replications in a sp lit-p lot design .

Experimental layout, sp lit-p lot design

The size o f the indivi^vial plots should be as large A*y pcssiblc war. a minimum for most crops of 5 x 10 m. In determining the size of the plots, account must be taken in case of a row crop on exclusion o f border rows (2 ), minimum number o f rows required for yield records (5), minimum number of rows required for recording plant development for different growth periods (3 ), and crop samples for determining dry matter production during different crop growth periods (5). The experimental layout should include provision for irrigation ditches or pipes with measuring devices, drain ditches, access strips between plots and separating borders between plots and ditches to reduce lateral movements o f water. Borders between plots should be as narrow as possible.

«3

D ATA COLLECTION

To allow a full evaluation o f the relationship between yield and water use and for experimental data to be useful to other locations, a balanced data set on site, crop, climate, soil and water management must be collected. The data set to be collected depends on the purpose for which it will be used. Full use must be made of related data already available for the area of study. Collection and recording o f data should follow a standardized form using an appropriate time scale depending on the event lo be recorded .

There is no optimum data set, but there is a minimum data set related to the type o f experiment and the purpose for which the data are to be analysed.

An indication of data requirements is given in the following checklist V. A subjective subdivision has been made in relation to type of experiment:

1. Field tria ls remote from research stations for crop performanceand comparative analysis at different sites and seasons.

U. Site experiments for crop performance and water use studiesfo r planning and design purposes.

111. Detailed experiments for testing water and crop productionmodels requiring extensive instrumentation, freoueni observations and samplings and a balanced set o f all relevant data.

Coding includes: a - needed 0 once

b ■ desirable 00 before and after growing period

c - helpful 1 daily

7 weekly

fortnightly

s selected times

c continuous

The checklist is primarily oriented toward grain crops but can, with adjustment, also be applied to other crops.

y A lso based on the outcome o f the F A O C ^ lP O C o n fe r e n c r o r s o il -w eathei^rop relations, Canberra, May 1976

C H E C K L IS T FOR D A T A ACQ U IS IT IO N FROM E X P E R IM E N T S

64

LO C ATIO N : 1,11,111; location name; y ea r/ p en o d ; latitude;longitude; altitude; surroundings; exposure; slope and r e l i e f

C U L T U R A L O P E R A T IO N S : I, I I , HI; land/plot h is to ry ; land preparation ;f e r t i l i z e r s ; weed , pest and d isease c o n tro l ; plot layout; ir r iga t ion method

CROP M A T E R IA L : 1, I I , 111; crop species and cu lt iva rs ; seed ireatmeni;sowing ra te , depth, and spacing and sowing method;III germination test

CROP H A ZA R D S 1,11,111; pest and d isease occu rrence ; w e e d s ; hail

C L IM A T E :

An agrom eteoro log ica l station should be established at o r near the experimental f ie ld . The station should be surrounded by an irr iga ted fie ld o f at least 100 x 100 m, covered hjr a short c rop . The station should be at least 10 x 10 m with short g rass as ground co ve r . Minimum observations should include; ( i ) temperature, maximum and minimum; ( i i ) r e la t iv e humidity (wet and dry bulb thermometers); ( in ) precip ita tion (ram gauge); ( i v ) wind (wind to ta l iz e r ) ; ( v ) sunshine duration (Cam pbell-S tokes r e c o rd e r ) ; and ( v i ) evaporation (c la ss A pan). Radiation measurements at the station o r nearby are recommended. Automatic record ing instruments such as thermograph and hydrograph can be useful but should be placed within the Stevenson sc reen , p re fe rab ly with a non-record ing instrument. W here this is not poss ib le , automatic record ing instruments should be checked for re l iab i l i ty at frequent in terva ls . The station should be established in co llaboration with the National M eteo ro log ica l S e rv ic e . F o r selection of instruments and observation p ra c t ic e s , the national accepted standards a re normally fo llowed. (S e e FAO Irr iga t ion and Drainage Pape r No . 27, A gro -m eteoro log ica l Field Stations, 1976. )

1 11 1111. temperature *7 “ i

2. humidity max/min 1 "1 “13. precipitation “14* wind ^7 “ 1

sunshine •1radiation b

snow b a as s s

•o il tamperature *>1 *1

SOI L ;

Detailad aoll tn/onnation is required which, in addition to general information (parent m ater ia l, dra inage, presence o f stones o r rock outcrops, evidence o f e ros ion , m icro- r e l ia f and slope) should include a description o f the individual soil horizons (s ee G a iA ^ la es fo r D es c i ip a o n , F A O , Ml 70605).

*5

1 n ni•oil type a^ a^

•oil texture a a ao o o

bulk density c a ao o o

fert i l ity c b aoo oo oo

pH c b aoo oo oo

available water b a ao o o

retention curve c * ao o o

infiltration rate b a ao o o

hydraulic conductivity a^

ECe b a ao oo oo

SAR c^ b a^o o o

W A TE R :

Measurements include soil water and in and outflow of water. Significant results of experiments depend almost exclusively on the accuracy with which the measurements are carried out.

Soil water measurements are carried out by; ( i ) soil water sampling for each treatment at different soil depth (soil layers ); and ( i i ) tensiometers (range 10 to 70 cbar or up to about 40 percent depletion leve l) and gypsum blocks (range 30 to 90 percent soil water depletion) in s ta l l^ at different soil depths for each treatment with 2 to 3 replications per plot. Readings should be made daily and using averages for each plot and each treatment. Design with four treatments and four replications would require about 1(X) devices (4 treatments, 2 or 3 replications, 3 locations per plot at 3 depths). For determining the water balance the amount of irrigation water applied, drain outflow, and effective rainfall must be measured by flumes (open conducts), flow o r ventun- meters (closed conducts) and ram gauges.

I II III

•oil water volume ‘>00 astension * .groundwater

depth *>00 • k * Uquality *>00 *0 0 • u

applicationdepth bc ac •cfrequency •c •cefficiency »>o • •

water quality ‘ >0 • u • utemperature b0 • u • uIn/out flow •c •c *c

66

CROP DEVELOPMENT:Adequate records should be made on dates of crop development periods for each treatment requiring almost daily inspection together with crop observations, e .g . wilting, stunted growth.

I 11 III

sowing ao *o ®o

emergence co “ o ô

10% cover c a ao o o

full cover b a ao o oflower initiation »>o *o50% riowenng co “ o *o

npenmg “ o ‘ o ®oharvest ao ao “ o

CROP GROWTH AND YIELD:For analysing yield response to water, crop observations and crop samples during the growing penod are required since final yield alone frequently provides an insufficient indication on crop growth and yield of the effect of water deficit during different growth penod s.

plants /m

tiUcrs/plant

head bearing tillers

LAI

crop height

1 11 Hi

b a ao o o

c b ao o oc b ao o o

b as s

bs •ssample for dry matter at nower initiation »>o “ o

50% flowenng “ onpening ‘ oharvest b a^ aô o o

economic yield •o ®o “ o

1000 gram weight ô ‘’o *ogram quality ô *>o *o

seed/head bo •oseed/plant •>o ‘ oroot/plant 'o •oroot development/depth ô

67

5. FV'Al I ’ ATION AND PRESENTATION OF RESULTS

All collected data should be examined indmdually for accuracy, reliability and consistency. Differences between treatments are to be analysed statistically.The relationships between yield and water deficit can be evaluated in a manner similar to that given in this publication. If the yield-water relationships show a wide variation within treatments, and if the yield response factors (ky) are markedly different from those presented, a further evaluation and interpretation of the results should be conducted in the light of limiting factors that may have been overlooked, anexperiment conducted with unadpated varieties or with hidden adverse effects from poor soil or with conditions or excessively high evapotranspiration.

The presentation of the final evaluation of the results will depend on the nature of the user. The presentation to planners, engineers, agronomists, should include the appropriate supporting research information obtained during the course of the experiment, whereas presentation to farmers should adopt a more practical approach whereby the results are expressed in clear guidelines on depth and interval of irrigation water as related to expected yields. This may also take the form of actual demonstration on the farm.

PART B

CROP AND WATER

ALFALFA

Alfalfa ( Medicaflo satvya) vs believed lo have originated in the Mediterranean region. It is grown as a forage crop, either for fresh produce or for hay. The crop IS grown under a wide rar^e of climates where average daily temperature during the growing period is above 5 ^ * The optimum temperature for growth is about 25®C and growth decreases sharply when temperatures are above 30^C and below lO^C- In warm climates the production is higher under dry as compared to humid conditions. A lfalfa can be used as an important break crop in the rotation and most crops can follow alfalfa with the exception of certain root crops such as sugarbeet, because of the high amount of root residue left in the soil.

Alfalfa IS a perennial crop and produces its highest yields during the second year of growth. In climates with mild winters, alfalfa is grown for 3 to 4 years continuously, but m continental climates with cold winters it is grown for 6 lo 9 y «d r s , with a dormant period in winter. The crop is also grown as a short season annual crop. Following seeding, the crop takes about 3 months to establish. Number of cuts vanes with climate and ranges between 2 and 12 per growing season. A lso , yield per cut for a given location varies over the year due to climatic differences.

Water use by the crop in relation to its production is high when compared to other forage crops such as forage maize, and when economic conditions permit alfalfa is replaced by maize as a forage crop.

Alfalfa IS successfully grown on a wide variety of soils, with deep, medium textured and well-drained soils being p re fe r red . Fert i l ize r requirements vary with production level and are 55 to 65 kg/ha P and 75 to 100 kg/ha K. V Alfalfa ts capable of fixing atmospheric nitrogen which meets its requirements for high yields. However, a starter of approximately 40 kg N is beneficial for good, early growth.

The crop is moderately sensitive to soil salinity. Yield decrease related to electrical conductivity (ECe of extraction saturated paste in mmhos/cm) is : 0% at ECe 2.0 mmhos/cm, 10% at 3 .4 , 25% at 5*4, 50% at 9 .8 , and 1(X)% at ECe 15-5 mmhos/ cm.

WATER REQUIREMENTS

Crop water requirements (ETm) are between 800 and 1 600 mm/growing period depending on climate and length of growing period. The variation in water requ irements in each cutting interval for alfalfa is similar to that during the total growing period from sowing to harvest for other crops. The kc value is about 0.4 pist after cutting, increasing to 1.05 to 1*2 just pnot to the next cutting with a mean value of 0.85 to 1 . 05* For seed production, the kc value is equal to 1.05 to 1.2 during full cover until the middle of flowering, after which the kc value is reduced sharply.

y Fert i l ize r requirements (kg nutrient/ha) o f high-producing varieties under irrigation; accurate amounts are to be obtained from local research results or to be determined by experiments, soil testing and plant analysis and evaluation of economic conditions. Conversion: 1 kg P • 2.4 kg PyO^, I kg K • I • 2 kg K7O.

7 0

WATER SU PPLY AND CROP YIELD

To stimulate root growth, the young stand should be irrigated frequently because root development is adversely affected by dryness. During each cutting interval the amount of total green matter produced increases to a maximum at the stari of flowenng when the quality for hay production is also at its best. To enhance growtfi, irrigation is normally applied just after cutting. When irrigation is applied just before cutting the top soil may still be wet at the time of cutting, hampering cutting and causing the cut matenal to mould more easily.

Excess irrigation may cause reduced soil aeration which is particularly harmful TO the crop. Dunng winter, when the crop is dormant or growing very slowly, the crop will tolerate short penods of flooding without causing much damage to the later growth of the crop.

The relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ETm) is given in Figure 6. Within a certain range of relative evapotranspi ration deficit (0 to 0.4 ), the yield response factor Cky) for both fresh and dry yield is smaller than one. This implies that water utilization efficiency (Ey) (kg of produce/mi of water) increases in this range of relative water deficit.Under conditions of limited water supply, overall production is increased by extending the area under irrigation rather than by meeting full crop water requirements over a limited area. A lso, the effect of a reduced water supply on yield of alfalfa is less pronounced than that of many other crops that have ky' values greater than one dunng the period of water shortage. Where cropping of several crops is involved, the irrigation supply to alfalfa may be reduced in favour of more son •sitive crops.

10 09 0 8 07 06 0 5 04 OS 02 0

Fig. 6

Relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ ETm) for alfalfa

For calculation example sec p. 40 and Chapter VI.

To reduce peak demands for water during the hot summer months, a dormancy ponod dunng these months is sometimes practised in North Afnca . Water savings •ro utilized dunng spnng and autumn when climatic conditions allow high yields with relatively lower water roquirements. Where the crop is grown for seed, effective water savings mav be made by timing the seed production dunng the penod when normal water dcmaruls of a forage crop would be high.

71

The 'drought tolerance* o f a lfa lfa , sometimes claimed during p en o d t o f Jo^ water requirem ents, appears to be due to ns extensive rooting system which enab le, the crop to draw water from a la rge soil volume.

CUTTING IN TE R V A L

Cuts are normally taken at the start o f flow ering when the vegetative growq^ slows down. Tem perature has a pronounced effect on cutting interval and cutting interval at d ifferen t mean daily temperatures is :

Tmean, °C 10 15 20 25 JO

In terva l, days (100) 50 3 5 25 20 18

When water and other growth factors are not lim iting, a firs t indication o f the time and number o f cuts for a given location can be obtained from the summation o f daily mean temperature (T ) above 5°C and the time o f cut is found when the aum T - 5 • 500 to 550 degree days (fo r example see Figure 7)-

^*8* 7 Example o f cutting interval over the growing periodo f a lfa lfa

W A T F R u p T A K F

AltaUa nas a deep rooting system extending up to 3 m in deep soils. The maximum root depth is reached after the first year. The crop can draw water from great soil depth and Uttle response to irrigation has been shown with groundwater tables at 2 m or higher. Normally, when the crop is fully grown, 100 percent of the water is extracted from the first 1 to 2 m soil depth CD » 1-2 m). When maximum evapotranspiration (ETm) is 5 to 6 mm/day, about 50 percent of the total available soil water can be depleted before the uptake of water from the soil affects crop evapotranspiration (o r p • 0 .5 ). A fter cutting full cover is reached in 12 to 20 days depending on temperature, and peak ETm is reached soon after.

IRRIGATION SCHEDULING

To obtain maximum yields under conditions where water supply is not limited, an adequate supply to meet crop water requirements during the whole cutting interval IS advisable. Irrigation practice for hay production van es with an application just after cutting to enhance rapid growth, or at the time when the crop is reaching full cover and water requirements are near maximum. Irrigation imm ^iate ly following removal of the cut crop is often practised on land difficult to irr iga te . Late application may result in soil remaining wet, thus delaying the drying of hay on the ground* For conditions free from water stress and depending on the leve l of maximum evapotranspiration (ETm ), a soil water depletion level of about 50 percent of the total available soil water (p ■ O . j ) » » permissible.

IRRIGATION VFTMODS

burtacc irrigation is commonly used in alfalfa production. The most common method is border irrigation. Contour irrigation and wild flooding arc sometimes practised. Where water is scarce o r the soil permeability is high, water is supplied' by overhead sprinkling.

YIELD

Crop yield vanes with climate and length of total growing period. Good yields after the first year are in the range of 2 to 2 .5 tons/ha per cut (hay with lt> to 15 p e r cent moisture) of about 25 to 30 day cutting interval. For example, Hofuf, Saudi Am bia, 28 ton/ha of hay over 310 days involving 12 cuts; DaviS| California, under expenmental conditions, 22 ton/ha of hay over 200 day growing period involving 7 cut*. The water utilization efficiency for harvested yield (Ey ) of hay with 10 to ISporcemt moiature la 1-5 lo 2.0kg/m) after the first year. The moisture content of freah green matter is about bO percent. From l8 to 20 percent of the dry weight IS protein.

BANANA

Banana (Musa spp.) is one of the mcsi imporiant tropical frutts. Ripe banana fruits are sugary and eaten raw; unnpe fruits, called plantains, are cooked and provide a starchy food with nutritional value sim ilar to potato. Total world production o f banana is about J9 million tons o f fresh fruit.

The cultivated banana is believed to have originated in the lowland, humid tropics in Southeast Asia and is mostly grown between and S of the equator.A mean temperature of about 27®C is optimal for growth. Minimum temperature for adequate growth is about 16°C, below which growth is checked and shooting de layed . Temperatures below 8®C for long periods cause serious damage. Maximum temperature for adequate growth is about 38^C, depending on humidity and the radiation intensity. Bananas are day-neutral in their response to daylength.

A humidity of at least 60 percent o r more is p re ferab le . Strong winds, grea ter than L m/sec, a rea major cause o f crop loss due to the pscudostems being blown down. Under high wind conditions windbreaks are des irab le .

Bananas can be grown on a wide range of soils provided they arc fert ile and w e ll-d ra in cd . Stagnant water will cause diseases such as the Panama disease. The best soils are deep, well-drained loams with a high water holding capacity and htunus content. Optimum pH is between 5 and 7. The demands for nitrogen and especia lly potash are high. Since the early stages of growth are cr itica l fo r later development, nutrients must be ample at the time of planting and at the start o f a ratoon crop. Short intervals between fe r t i l iz e r applications, especia lly nitrogen, are recommended. F e r t i l iz e r requirement s are 2(X) to 400 kg/ha N , 43 to 60 kg/ha P and 240 to 480 kg/ha K per year .

Banana is ve ry sensitive to salinity and soils with an ECe o f less than 1 mmho/ cm are required fo r good growth.

Banana, 2 to 9 m ta ll, bears leaves on a pseudostem consisting of leaf stalks. The flowering stalk emerges (shooting) from the pseudostem and produces a hanging bunch o f f low ers . Fruits are formed on 'hands* with about 12 fingers; each bunch contains up to 150 fingers. A fter harvest the pseudostem is cut. The underground stem (corm or rhizome) bears several buds which, after sprouting, form new pseudostems, o r so-called suckers. They are removed except for one o r two which provide the ratoon crop.

Banana is normally multiplied vege ta tive ly . S evera l types of suckers can be used. The development of the plant can be divided into three per iods : vegetative, flowering and yield formation. The time from planting to shooting (vegeta tive ) is about 7 to 9 months, but with lower temperatures at higher altitudes o r in the subtrop ics , up to 18 months. The time from shooting to harvest (n ow en ng and yield formation) is about 90 days. In tropical ]pwlands the time to harvest o? (he next ratoon crop is about 6 months. The number o f ratoons va n es . The average Ufe o f a commercial plantation can be from 3 to 20 years ; with mechanical cultivation the economtc h fe is often 4 to 6 years . Some varie ties are replanted a fter each harvest.

Planting distances vary according to var ie ty , climate, soil and managciaeni and are between 2 x 2 m and 5 x 5 tn, corresponding to a density of 400 to 2 500 plants/ ha. On steep slopes contour planting is practised. The crop is sometimes interplanted or is used as a nurse crop for crops such as cocoa.

"4

Fig. 9Development of banana (Champion, 1963)

WATER REQUIREMENTS

Being a long duration crop, the total water requirements of banana are high. Water requirements per year vary between 1 200 mm in the humid tropics lo 2 200 in th« dry tropics. For rainfed production, average rainfall of 2 000 to 2 jOO mm per year, well-dist*nbuted, is desirable, but banana often grows under less rainfall.

In relation to reference evapotranspiration (ETo) the maximum water requirements (ETm'' > o It-termined with the crop coefficient (kc), or ETm - V

kc

r T

J F M A M J J A S O N D

SMbmaus*! climateFirst-year crop, March planting:Humid, light to mod. wind - - .65 .6 Dry, sirongwind - - .5 >45

• J J

.5 .65. 7.0

.05 .95 1.0 1.15

1.01.2

1 . 0 1 . 0 1.151.15

Second with ratoon starting in February: Humid, hght to mod. wind 1.0 .8 . 7 5 Dry, atrong wind 1.15 *7 . 7 5 J -9

.9X.l

1.05 1.05 1.25 1.25

1.051.25

1.0 1.0 1.2 1.2

IC SBISA) £ )L -« UMonths following planting: 1 2 3 4 5 6 7 0 9 10 11 12 \ 3_ 14__ 15

.4 .4 .45 *5 *o . 7 • 05 1.0 l . l 1.1 .9 .8 .8 .95 'suckering shooting harvesting

75

W A i i .K cL IT 1 'I A N T K O L i l h L D

Banana requires an ample and frequent supply of water; water deficits adversely affect crop growth and yields. The establishment penod and the early phase of the vegetative period (0-1) determine the potential for growth and fruiting and an adequate water and sufficient nutrient supply is essential dunng this period. Water deficits in the vegetative pericxl (1) affect the rate of loaf development, which in tuni can influence the number of flowers in addition to the number of hands and bunch production.

The flowering period (2) starts at flower differentiation, although vegetative development con still continue. Water deficits m this period limit leaf growth and number of fruits.

Water deficits m the y ie ld formation period (3) affect both the fruit size and quality (poorly filled fingers). A reduced leaf area will reduce the rate of fruit filling; this leads, at harvest time, to bunches being older than they appear Ho in-lquently the fruits are liable to premature ripening during storage.

The ratio between relative yield decrease and relative evapotranspiration deficit (ky) IS 1.2 to 1.35, with little difference between different growth p*' * ’(Fig* 9)* For calculation examples seep . 40 and Chapter VI.

t u

10 09 OS 0^ OS 0& 04 0 ) 02 Oi

Fig. 9Relation: hip i o L a i i v o _\ . l .Jdecrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - FTa/ FTm) for banana

0

01

02

01

04

05

OS

07

oa

0> 2rs

Regular water supply under irrigation over the total growing season as ^c:iipared to rainfed production with seasonal differences in water supply produces taller plants, with greater leaf area, and results tn earlier shooting sjkd K i^er yields. Interval between irrigation has a pronounced effect onylcldSa with h i^ c r yields being achieved when intervals are kept short. Under condittons of limited water supply, total production will be higher when full crop water requirements are met over a limited area than when crop water requirements arc partially met over an extended area.

76

W T V ‘ r'TAK F

The banana plant has a sparse, shallow root system. Most feeding roots are apread laterally near the surface. Rooting depth w ill generally not exceed 0.75 In general 100 percent of the water is obtained from the first 0-5 to 0 .8 m soil depth (D - 0 .5 -0 .8 m) with 60 percent from the first 0 .3 m. With maximum evapotranspiration (ETm) o f 5 to 6 nun/day, a 35 percent depletion of the total available soil water should not be exceeded (p - 0.35).


Since a depletion of total available soil water in excess of about 35 percent .i.g the total growing period is harmful to growth and fruit production, frequent

irrigation is important. The irrigation interval will depend on ETm and the soil water holding capacity in the rooting depth and may vary from 3 days under high evaporative conditions and light soils up to 15 days under low evaporative conditions and high water retaining soils. When rainfall and irrigation water is limited, it is advantageous to reduce the depth of each water application rather than to extend the irrigation interval.

IRRIGATION METHODS

Overhead sprinkler systems with small application at frequent intervals are commonly used in commercial banana plantations. Surface irrigation methods include the basin, furrow or trench irrigation systems. The trench system also serves as a dram during the rainy periods. A lso drip irrigation is used; with drip irrigation under conditions of high evaporation, low rainfall and particularly when irrigation water contains even a small amount of salt, accumulation of salts at the boundary of wet and dry soil area w il l occur. Under such conditions leaching will often be needed alncc banana plants are highly salt-sensitive and damage to the crop can otherwise easily occur.

YIELD AND Q U ALITY

Yields can vary enormously. Under poor management yields are usually highest for the planted ( f ir s t ) crop and decline for the ratoon crops. Under intensive management with correct desuckermg and control of pests and diseases, yields from the first ratoons are usually higher than for the plant crop. Good commercial yields of banana are in the range of iO io 6U ton/ha. The water uiilization efficiency for harvested yield (Ey ) of fruits, containing about 70 percent moisture, is 2 .5 to 6 hg/m^ for o ,J '. ' »o k w’ ' for ratoon crops.

BEAN

Common bean CPhaseolus vulflana) is known under different names (French bean, kidney bean, snap bean, runner bean, string bean). It can be grown as a vegetable crop for fresh pods or as a pulse crop for dry seed. World production of dry beans is about 18. 7 million tons from about JO million ha and green beans 2.2 million tons from 0.^ million ha.

Common bean grows well m areas with medium rainfall, but the crop is not suited to the humid, wet tropics. Excessive ram and hot weather cause flower and pod drop and increase the incidence of diseases. Optimum mean daily temperatures range between 15 and 20®C. The minimum mean daily temperature for growth is 10®C, the maximum 27°C. High temperatures increase the fibre content in the pod.Germination requires a soil temperature of 15®C or more, and at 18®C germination takes about 12 days, and at 25®C about 7 days. Most bean varieties .are not affected by daylcngth. The length of the total growing period vanes with the use of the product and IS 60 to 90 days for green bean and 90 to 120 days for dry bean.

The crop does not have specific soil requirements but fr iab le, deep soils with pH of 5. 3 to 6.0 are pre ferred . Fert i l ize r requirements for high production are 20 to ^0 kg/ha N , iO to 60 kg/ha P and 50 to 120 kg/ha K . Bean is capable of fixing nitrogen which can meet its requirements for high yie lds. However, a starter dose of N is beneficial for good early growth. The crop is sensitive to so il-bom e diseases and should be grown in a rotation; in the subtropics in the USA wheat, sorghum, onion and potato are common rotation crops, whereas m tropical A frica and Asia maize, sweet potato and cotton are common.

Normal sowing depth is about 5 to 7 cm. Spacing depends on va n o tv . i ish types (e rect ) normally have a plant and row spacing of 5 to 10 x 50 to 75 cm, while pole-type (climbing) are 10 to 15 x 90 to 150 cm, Po le beans are also often grown on hills spaced 90 to 120 cm apart. Other spactngs are possible, and these depend on the method of harvest.

Common bean is sensitive to soil salinity. The yield decrease at different levels of ECe is : 0% at ECe 1.0, 10% at 1,5. 25% at 2.3, 50% at 3-6 and 100% at ECe6. 5 mmhos/cm.

W ATER REQUIREMENTS

Water requirements for maximum production o f a 60 to 120-day crop vary between 300 and 500 mm depending on climate. The water requirements during the ripening period depend very much on whether the pod is harvested wet or dry. When grown for its fresh product, the total growing period of the crop is relatively short and during the ripening, which is about 10 days long, the crop evapoiransptretion is relatively small because of the drying of the leaves. When the crop is grown for seed the ripening period is longer and the decrease in crop evapotranspiration is relatively greater. The growing period depends on the number of pickings, and when 3 or L pickings are taken the harvest period is 20 to JO days. Crop coefficient Ckc) relating reference evapotranspiration (E T o ) to water requirements (ETm) for d if fe raat development stages is , fo r common bean, green: during the initial stage 0 .3-0*^ (15 to 20 days); the development stage 0.65-0,75 ( IS to 20 d ^ s ) ; the mid-season stage 0,95-1.05 (20 to JO days); the late-season stage 0 .9 -0 .95 (5 to 20 days) and at harvest 0 .85-0 .9- For common bean, dry', the kc value is : during the tmttal stage

7 8

<15 to 20 days); the dcvclopmeni stage 0 ,7 -0 .8 (15 to 20 days); the mid- ••eaon stage K05-1 .2 (35 to ^5 days); the late-scason stage 0.65-0.75 (20 to 25 days); and at harvest 0 .23-0.3.

W A. ‘ r SUPPLY AND CROP YIELD

Water supply needed for maximum yield for both fresh and dry produce is similar during much of the growing period but varies during the ripening period. For green beans supply is continued just p r ior to the last picking, but for dry bean it is discontinued about 20 to 25 days before crop harvest. With one picking only the harvest period is concentrated. This can be achieved to some extent by the timing of water supply so as to induce a slight water deficit to the crop during the ripening period and a soil water depletion to about 50 percent of the total available water may hasten the onset of maturity. Concentration of the harvest period is more easily achieved for bush than for pole types. The former normally have a more uniform ripening period.

The growth periods of a common bean crop are;

green bean dry bean

0 estabh shment 10-15 days 10-15 daysI vegetative (up to first flower) 20-25 20-252 flowering (including pod setting) 15-25 15-253 yield formation (pod development

and bean f i l l in g 15-20 25-30. pening 0-5 20-25

Go -90 90-120 days

The relationships between relative yield decrease and relative evapotrans- piratiOn deficit are given in Figure 10. For calculation examples seep . -dO and Chapter VI

f t10 OS OS or os OS 04 05 02 01

f t

1 iK* I" Relationship between relative yield decrease U - Va, Ym)and relative evapotranspiration deficit (1 - ETa/ETm) for bean

7 ^

However, a severe water deficit during the vegetative period (1 ) generall> re tard .1 plant development and causes non-uniform growth.

During flowering (2) and yield formation G ) frequent irrigation results m the highest response to production, although excess water increases the incidence o f d iseases, particularly root rot. When nitrogen is supplied to the crop In ti'e form o f mineral fe r t i l iz e r , irrigation should be accompanied by adequate application - f nitrogen fe r t i l iz e r in order to maximize yield.

When water supply is limited, some water savings could be made dunng the vegetative period (1 ) and, for dry bean, also during the iipening period wi;*r*ui greatly affecting y ie ld , provided water deficits are moderate. ,:*xxiuctlon Ishigher when full crop water requirements are met over a liudtcd area ihu"» wl lh « cultivated area is extended under limited supply conditions.

WATER U PTAKE

The tap root of the bean plant may reach a depth of 1 to 1.5 tn- Tht Ut **rsl root system is extensive and is mainly concentrated in the first 0. J m. At emerk^e.icc, the rooting depth is about 0.07 m, at the start of flowering 0.3 to 0 .^ m, and at maturity 1 to 1,5 m. Water uptake occurs mainly in the first 0-5 to 0.7 m depth (D - 0 .5 -0 .7 m). Under conditions when ETm is 5 to 6 mm/day, ^0 to 50 percent of the total available soil water can be depleted before water uptake is affected (p - O.ii-0.5 ).


When the bean crop is grown with supplemental irrigation, water supply should be directed toward meeting water requirements during the establishment period (0) and the early pai~t of the flowering period (2). When the crop is grown under full irr igation, the soil water depletion during the flowering ( 2 ) and yield formation (J) periods should not exceed ^0 to 50 percent of the total available soil water (p - O .Z-0.5). When the crop is grown for dry seed the depletion level during the ripening period (^) should not exceed 60 to 70 percent. Water stress in the plant can be detected by eye because the leaves turn dark bluish-green in colour.

YIELD AND Q U ALITY

Water Juring lae jie iu lormation period (3) gives rise to small, shortdiscoloured pods with malformed beans. A lso, the fibre content of the pods ta higher and seeds lose their tenderness. Good commercial yield in favourable environments under irrigation is 6 to 8 ton/ha fresh and 1 . 5 to 2 ton/ha dry seed. The water utilization efficiency for harvested yield (Ey ) for fresh bean containing 80 to 90 p e rcent moisture is 1 .5 to 2.0 kg/m* and for dry been containing about 10 percent moisture, O.J to 0 .6 kg/m*.

CABBAGE

Cabbage CBrassica oleracea var. capitata) originates from the south and western coast of Europe. Annual world production is about 21 million tons o f fresh heads from 1. 1 million ha.

For high production the crop requires a cool , humid climate. The length of the total growing period va n es between 90 (spring-sown) and 200 (autumn-sown) days, depending on climate, variety and planting date, but fo r good production the growing period IS about 120 to 140 days. Most varieties can withstand a short period of frost of -6®C, some down to -10®C. Long periods (30 to 60 days) of -5°C are harmful. The plants with leaves smaller than 3 cm will survive long periods of low temperature but when the leaves are 5 to 7 cm, the plant will initiate a seed stalk and this leads to a poor quality yie ld. Optimum growth occurs at a mean daily temperature of about 17®C with daily mean maximum of 24°C and minimum of 10°C. Mean relative humidity should be in the range of bO to 90 percent.

Generally, the heavier loam soils are more suited to cabbage production.Under high rainfall conditions, sandy or sandy loam soils are preferab le because of improved drainage. The fe r t i l iz e r requirements are high: 100 to 150 kg/ha N , 50 to65 kg/ha P and 100 to 130 kg/ha K .

Cabbage is moderately sensitive to soil salinity. Yield decrease due to soil salinity at different leve ls of ECe is : 0% at ECe 1.8, 10% at 2.8 , 25% at 4 .4 , 50% at 7.0 and 100% at ECe 12.0 mmhos/cm

Row spacing is dependent on the size of heads required for markets or between 0-3 and 0. 5 ni fo r heads of 1 to 1.5 kg each and 0. 5 and 0 .9 nn for heads up to 3 kg each. An optimum production can be reached with a plant density in the range o f 30 000 to 400(X) plants/ha. Planting can be by direct seeding with a se€:d rate of 3 kg/ha, or by transplanting from open field beds and from cold frames which are used to protect the

) frcm cold during germination and e a r ly plant development.crop

ill-grown cabbage

Cabbage is characterized by slow development during the first half o f the growing period, which may be 50 days for early maturing and up to 100 for autumn-sown, late maturing varieties (estabhshmeni and vegetative periods, 0 and 1). During the following periods (yield formation and npening periods, 3 and 4) the plant doubles Its weight approximately every 9 days over a total penod of 50 days. In the beginning of the yield formation period (3), head formation starts, followed by a sudden decrease m the rate of leaf-unfolding. Eventually, leaf unfolding ceases completely, whilst leaf initiation continues. This results in the formation o f a re s tr ic tive skin by the oldest folded leaves within which younger leaves continue to grow until the firm, mature head Is produced during the ripening period

81

of 10 to 20 days (4). Depending on variety , the head can be pointed or round, green or red, smooth or crinkled. Crop rotation o f at least 3 years is recommended toromtiat ^oil-l>ome diseases.

WATER REQUIREMENTS

Water requirements vary from 380 to 500 mm depending on climate and length of growing season. The crop transpiration increases during the crop growing penod with a peak toward the end of the season. In relation to the rafarence evapotranspiration (E T o ), the crop coefficient (kc) for cabbage is : during the initial stage 0 .4 -0 .5 (2 0 to 30 days); the crop development stage 0. 7-0.6 (30 to 3Sdays); the mid- scason stage 0.95- 1 1 (20 to 30 days), the late season stage 0. 9-1 ■ ' ’ o 20 days): and at harvest 0,8-0.95*

WATER S U P PLY AND CROP YIELD

The relationships between relative yield decrease and relative evapotranspiration deficit based on interpreted information are given in Figure 12. The response to water supply increases with development of the crop. During the slow development in the vegetative period (1), the crop yield is little affected by water deficit. Once rapid growth during y ie ld formation period (3) is reached, the yield depressing effect of limited water supply becomes increasingly pronounced until the end of the growing period. UrdoT conditions of limited water supply, a high total production is obtained by extending the area and partially meeting crop water requirements rather than by meeting full crop water requirements over a limited area.

i-Ul f t

Pig* 12 Relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration (1 - ETa/ETm) for cabbage

82

w a t e r u p t a k e

Cabbage has an extensive, shallow root system. The majority of the roots are found in the top 0.4 to 0 .5 m of the soil with a rapid decrease in root density with depth. Normally 100 percent of the water is extracted from this layer (D - 0 .4-0. 5 m). Under conditions when ETm • 5 to 6 mm/day, the rate of water uptake by the crop starts to reduce when the available soil water has been depleted by about 35 percent (p - 0.35).


Depending on climate, crop development and soil tvpe, the frequency of irrigation varies between 3 and 12 days. If available water supply is limited, early irrigations should not be practised unless these can be continued until the end of the crop growing period. Water savings should preferably be made in the beginning ot the crop growing penod.

IRRIGATION METHODS

Furrow, sprinkler and trickle irrigation are used. However, the acreage under subsoil irrigation, which gives generally better results, is increasing. With subsoil irnga iion , the depth of the water table is maintained between 0.3 and 0.7 m in fine, sandy loam and between 0.7 and 1.1 m in loam soils.

YIELD AND QUALITY

Under rainfed conditions, yields of 25 to 35 ton/ha fresh heads are normal, with a maximum of about SO ton/ha when sprayed and well- fertil ized . Under ideal climatic conditions and good irngaiton and crop management, yields can be as high as 85 ton/ha. The utilization efficiency for harvested yield (Ey) for heads is about 12 to 20 kg/m>.

The average water content of cabbage heads is about 90 percent, with a high vitamin B, C and calcium and phosphorous content. Smaller heads of poor quality are produced when the crop is grown under limited water supply, particularly during the later part of the growing period.

CITRUS

Citrus species a re perennial m growth habit. The moal commonly cultivated spec ies a re Citrus auranufolia ( l im e ) . C i t rus aurantium (sour o r S ev i l le o range ) , C itrus g r and IS (pummelc, shaddock), Citrus hmon (lemon), C itrus m < ^ ^ (c i t ron ) , C itrus paradisi (g rape fru i t ) , Citrus reticulata (mandarin. tangenneT and Citrua ainensis (sweet orange ) . P resen t world production o f citrus is about 50 million tona of fresh fru it , o f which 70 percent is orange , percent mandarin and langerUic,9 percent c i t ron , lime and lemon and 7 percent grapefru it . The quantity oi fresh fruit entering international trade is only exceeded by banana.

Citrus or ig inates from the wet tropics in Southeast A s ia , but la rg e -s ca le commercial production is found in the subtropics under irr iga t ion . In addition to fresh fruit and ju ice, citrus is grown fo r production of oil and c i tr ic acid.

Citrus t rees normally start bear ing fruit from the third y ea r a fter planting, but economic y ie lds are general ly obtained from the fifth year onward. For f lower ing in spring a period o f rest or reduced growth is needed. In the subtropics the low winter temperature induce: this rest per iod, but in the absence o f sufhcient ch i l l ing, the rest period can be induced by water d e f ic i t * .

Only a small percentage of the f lowers produce mature fru its ; during the f lower ing per iod fall of the weaker younger fruits occurs naturally and thia is called 'June drop* in the northern or the 'December drop* in the southern hemisphere. Fruits take 7 to 1 months from flowering to maturity, corresponding to a harvest season from October/November to May/Juno m the northern hemisphere and from Apr i l/May to November/December in the southern hemisphere. Lemons, how ever , have a longer f lower ing period and a re harvested throughout the year . For most cu lt ivars , pollination is necessary for fruit development.

During ripening the amount of acid decreases while the sugar and aromatic substances increase . The fruit is of prime qua l i ty when sugar content is high.P ick ing takes place when the fruits are fully mature. Colour is not always an indication o f fruit maturity. Degreening is conditioned by a period of cool weather.Green, mature fruits arc obtained in the humid t rop ics , and with ear ly o r late season harvests in the subtropics. In the subtropics, fruits that have attained full co lour, ye l low o r orange , in late autumn or early winter have been known to turn green again in spring, when not harvested. Fruits in the humid tropics lend to be la rge with thin, smooth r inds, a high juice content and lower total soluble solids and acid concentration*

Citrus is cultivated between and 40*^5, up to 1000 m altitude in thetropics and up to 750 m altitude in the subtropics. F o r la rg e -s ca le production geared toward export markets the crop is not suited to humid tropica because m E d i t ion to the dif ficulty of achieving the right fruit co lour, humidity increases the incidence of pests and d iseases . Only mandarins wil l to lerate humid conditions to a certain extent.

The optimum mean daily temperature fo r growth is 23 to 30^C. Growth is markedly reduced above J8®C and below 13®C. Ac t ive root growth occurs when soil temperatures are higher than 12^C. Most citrus species to lerate light frost f q r short periods only. Injury is caused by a temperature o f -3^C occurr ing o ve r several hours. Temperatures o f -S^C cause branches to wither and - 10®C general ly kil ls the tree ent ire ly , f l o w e r s and young fruits are part icular ly sensit ive to frost and are shed a fter v e ry short per iods o f temperatures slightly below 0®C. Dormant t rees are less susceptible to frost . Strong wind is harmful to citrus t rees because f lowers and young fruits fall eas i ly ; windbreaks are provided where necessary.

84

itrus is grown on soils that a re sufAcietitly aerated and deep to allow tap r o o i i u penetrate to the des ired depths (1 -2 in). Light to medium textured so ils , f r e e from stagnant water and sticky impervious layers are p re fe r red . A reas with a high water table should be avoided. Soil physical structure is o f grea ter importance than the chemical p ropert ies , provided sufficient magnesium and minor elements such a t l in e , copper and manganese are present in an available form. Soils with pH between 5 and 8 are p re fe r red . The annual fe r t i l iz e r requirements o f citrus are 1(X)X o 200 kg/ha N , 35 to ^5 kg^ha P and 50 to 160 kg/ha K . Adequate fe r t i l i ty is important for both fruit quality and yie ld.

Citrus trees are sensitive to a high salt concentration in the so il. Y ie ld decreases due to soil salinity a re : 0% at ECe 1.7 , 10^ at 2 .3 , 25% at 3 .3 , 50% at ^ .8 , and 1(X)% at ECe 8 mmhos/cm.

Propagation o f citrus trees is done mostly by bud gra ft ing , i . e . the insertion o f buds o f a desired varie ty on to a stock grown from seed of another va r ie ty . Normally citrus trees are transplanted. Planting distances vary according to soil conditions, the general topography, the varie ty and the type of tree to be planted, and are genera lly from ^ x ^ to 8 x 8. Planting may be square, rectangular, triangular or hexagonal. On steep slopes trees are planted in terraces o r along contours. T re e density v a n e s from 200 to 800 treer /ha. Young citrus orchards are often intercropped. In high rainfall areas permanent cov^t crops o r broad-leaved weeds may be des irab le , but in d r ie r areas the soil is often kept bare. I f an orchard is interplanted the companion crop should not strongly compete with the citrus trees for water and nutrients.A legume crop is often p re fe r red .

WATER REQUIREM ENTS

Citrus trees are evergreens and thus transpire throughout the year . W ater requirements for high production vary with climate, ground cover , clean cultivation or no weed control, species and rootstock. The water requirements for grapefruit are somewhat higher than for the other citrus species. In general total water requirements vary between 900 and 1 200 mm per year .

The crop coeffic ients (k c ) re lating ETm citrus to the re ference evapotranspiration (E T o ) fo r the subtropics with winter rainfall a re :

J F M A M ] J A S O N D

Large , mature trees providing • 70% tree ground cove r , clean cultivated . 7 ' . . . . . .65 .65 .7 .7 .7No weed control .9 85 •85 .85 .85 ,85 ,85 ,85 ,85 ,85 .85

W A T f t ‘

As a perennial crop the response o f citrus to water supply at a particular period of devclopmeni wiU depend greatly on the leve l of water supply p r io r to that period dunag the same growing season and also the leve l o f water supply duringp r e v i o u s .irow -

In genera l , when water is insuffic ient, growth is re tarded , leaves curl and drop I young fruits fall and fruits that mature arc def ic ient in juice and in fe r io r in quality. When the soil water depletion reaches permanent wilt ing po in t , t ree growth IS terminated and subsequently a f fects fruits and leaves , fo llowed by tw igs , branches and eventually the whole t ree .

New vegeta t ive growth m any yea r is influenced by residual e f fects of g fowth in previous seasons. The vegetat ive growth of young t rees determines their final tree Size and future fru it-bear ing capacity. F o r mature t r e e s , the growth v igour d e t e r mines the replacement rate of f ru i t -b ean n g branches. Any ef fect of water def ic it on root and lea f development may impair the number and size o f fruits la ter in the season. W ater de f ic i ts must be avoided when vegetat ive growth is most rapid. P n o r to f low er ing and fruit set, how ever , too v igorous , luxurious growth may impair production of high quality fruit.

In Citrus a rest period appears lo Uc ossontial tor f lower ing . The duration of the res t period determines the amount o f f lowers produced. The rest pe r iod , p r e f e r ably o f 2 months duration, can be induced either by low temperatures in winter (about 10®C) in the subtropics and in the tropics by a period o f water de f ic it (monthly rainfall o r i r r iga t ion <50 to 60 mm). The f lower bud initiation occurs during this rest period when vegetat ive growth is minimum. Water de f ic i ts can have, how ever , some harmful e f fects for long-term crop production as compared to when dormancy is caused by a cold pe r iod . (Dnce the rest p e i io d is ended, an adequate water supply is necessary because prolonged water defic its w il l not only delay f lower ing but also lead to o v e r production o f f lowers . This can result in low er yields during the next season and possib ly in subsequent seasons to a biennial fru it -bear ing cyc le . For lemons, water de f ic i ts in summer are commonly u^ed to start of f -season f l owonnc for \ ear-round production .

The f lower ing period is ve ry sensit ive to water de f ic i ts . W ater de f ic i ts d irec t ly reduce fruit set; also during this per iod nutrit ion, espec ia l ly n itrogen, is essentia l and adequate water is necessary to make the nutrients available to the crop. M o re o v e r , water de f ic i t during fruit set reduces yield by causing a heavy June o r December fruit drop.

Water de f ic i ts during June o r December (ea r ly y ie ld formation) can increase fruit shedding and reduce the rate o f fruit growth. A fte r June o r December drop , water de f ic i ts can affect the final fruit s ize . The increase m fruit s ize from June or December to maturity is highly dependent on water uptahe, and the rale o f enlargement of immature fruit IS an indication o f the need for irr igat ion. However , soil water depletions result ing in moderate water def ic i ts a fter July or January (yield formation and n p ^ in g ) can be des irab le because the content o f soluble solids and acids in the fruit is increased ; a lso , t ree growth is reduced which facil itates picking. In addition, a slight reduction in fruit s ize is often commercially des irab le . When soils are fine tcxtured, moderate water de f ic i ts a fter ear ly yield formation prov ide better soil aeration, and diseases such as roo t -ro t CPhvtophtora spp. ) may be prevented.

A more s eve re water def ic it during summer followed by irr igat ion may induce out-o f-season f lowering which general ly results in a worthless second fruit production and causes a possib le reduction o f y ield in the fo l lowing mam crop. Only lemon can produce all yea r round without harmful e f fects on tree growth o r y ie ld . F or Other citrus spec ies , the production of a second crop is a fairl'. that thetree has been short o f water at some stage.

Because o f the c a r r y - o v e r e f fects o f water de f ic i ts on t re e growth and later y ie lds , the relation between yield decrease and re la t ive evapotranspiration deficit only applies when y ea r to yea r water de f ic i ts are of sim ilar magnitude (F ig . j j ) . Sinco dota are la rge ly obtained from subtropical climates with winter ram/ail and where wtatar rainfall is sufficient to meet the crop water requirements in wuttar and ear ly spring.

85

86

the relanonsfiip tn Figure 13 applies la w ater deficits only during the period just p r io r to flowering to early harvest. However, variation in yield per tree is always likelv to be considerable.

- S

Fig, 13

Relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ ETm) for citrus

WATER UPTAKE

Most citrus species develop a single tap root. The lateral roots forrrt a horizontal mat of feeding roots with weakly developed root hairs. Root development is largely dependent on the type of rootstock used and on the characteristics of the soil p ron lc . Rooting depth va n es between 1.20 and 2 m. In general, 60 percent o f the roots are found in the first 0 .5 m, 30 percent in the second 0. 5 m, and 10 percent below 1 m, Wher water supply is adequate, normally 100 percent of the water is extracted from ih e f i r s i 1.2 to 1.6m CD - 1 .2 -1 .6m ) but under dry conditions the depth of water extracted below this depth increases. During prolonged periods of water defic it, soil water in a deep and well-drained soil may be utilized up to a soil depth of 2 or 3 m.


Peak water requirements are reached between flowering and June or December drop. In this period frequent irrigation is necessary. When ETm is 5 to 6 mm/day, the fraction of available soil water (p) m this period equals about but soil water depletion may be 60 to 70 percent from July or January to the end of autumn. During the latter period less frequent irrigation is advisable because during this period citrus

les^ sensitive to water deficits.

Irrigation scheduling requires great caution. C itrus trees demand good soil aeration and ovar-irrtgation is highly detrimental, particularly to young trees. Too frequent and heavy irrigations may affect root development and yield and lead to leeching of nutrients. In climates where winters are too mild to induce a rest period, irmgattoe ahoukd be withheld for 2 to 3 months.

IRRIGATION METHODS

i h e mo SI o m i n o i i ^ u i l c i r r i . t i c l t . o G > a t . t i . ■ * . : t . ga: . . \ eralfurrows between the tree rows), check irrigation (basins containing one or more trees) or flood irrigation (where citrus trees are planted on beds or ridges). Because of uneven water distribution and the difficulty of applying small amounts o f water the importance of surface irrigation for citrus is decreasing.

Sprinkler irrigation may provide a more uniform distribution of water and the possibility of applying the exact depth of required water. With the drip or micro- jet systems, water savings may be obtained because water is applied only to the root zone, leaving the remaining part of the soil dry. Sprinkler irrigation is also frequentlv used for frost protection.

«7

YIELD LEVELS

Within an orchard yield vanes greatly from tree to tree, while for a single t r o o y i e l d vanes from year to year. Sometimes a two-year fruit bearing cycle c r

Good yields of citrus are: orange - between 400 and 550 fruits per tree ; i t year corresponding to 25 to 40 tons per ha per year; grapefruit - 300 to 400 fnnis per tree per year and 40 to 60 tons per ha; lemons - 30 to 45 tons per ha per year; mandarin - 20 to 30 tons per ha per year- The water utilization efficiency for harvested yield (Ey) for citrus fruits is about 2 to 3 kg/m^ with a moisture content of the fruits of about 85 percent, except for lime which contains about 70 percent moisture,

COTTON

Cotton ( Goasvpmm hirsutmn) is grown for fibre and seed. Present world production is about 12, ' "iTlion tons lint and 36.4 million ions seed cotton from about 31.4 million ha.

The origin of cotton is still uncertain. The development of the crop is sensitive lo temperature. Cool nights and low daytime temperatures result in vegetative growth with few fruiting branches. The crop is very sensitive to frost and a minimum of 200 frost-free days is required. The length o f the total growing period is about 150 to 180 days. Depending on temperature and variety, 50 to o5 days are required from planting lo first bud formation, 2 5 to 30 days for flower formation and 50 to 60 days from flower Opening to mature boll. No clear distinction can be made in crop growth periods since vegetative growth is continued during flowering and boll formation and flowering is continued during boll formation.

a '1

! f ^

1

III1

1 ; 1 jj

Vi*W 1 >>

t1

Fig. 14 Growth penod i of cotton (after P . ' ' ' . Walker)

Cotton ts a short-day plant but day-neutral varieties exist. However, the effet:t of daylength on flowering is influenced by ten^erature. Germination Is optimum at temperatures of 18 to 30®C, with minimum of 14®C and maximum of 40^C. Delayed genaination exposes seeds to fungus infections in the soil. For early vegetative growth, temperature must exceed 20®C with 30®C ss desirable. For proper bud formation and flowering, daytime temperature should be higher than 20^C and night temperature

higher than but should not exceed 40 and 27®C respectively. Temperaturesbetween 27 and 32®C are optimum for boll development and maturation but above yields are reduced.

Strong and/or cold winds seriously affect the delicate young seedlings and at maturity will blow away fibre from opened bolls and cause soiling o f the fibre withdust.

Cotton IS extensively grown under rainfed conditions. Although the crop is relatively resistant to short periods of waterlogging, heavy rainfall, however, can cause lodging. Continuous ram during flowenng and boll opening will impair pollination and reduce fibre quality. Heavy rainfall dunng flowering causes flower buds and young bolls to fall.

Cotton IS grown on a wide range of soils but medium and heavy tcxtured, deep soils with good water holding characteristics are preferred. Acid or dense subsoils limit root penetration. The pH range is 5 .5 io 8 with 7 to 8 regarded as optimum. The fertilizer requirements of cotton under irrigation are lOO to l8o kg/ha N , 20 to 60 kg/ha P and 50 to 80 kg/ha K . Two-thirds of the nutrients are taken up during the first 60 days of the growing period. Nitrogen should be readily available at the start of the growing season; normally two applications arc given with one after sowing and the other prior to flowering. Phosphate is applied before sowing. Plant spacing normally vanes between 50/100 x 30/50 cm.

The crop is tolerant to soil salinity. Yield decreases at different HCe values are: 0% at ECe 7.7 mmhos/cm; 10% at 9*6, 23% at 13, 50% at 17 and 100% at ECe 27 mmhos/cm.

89

WATER REQUIREMENTS

Depending on climate and length of the total growing period , cotton needs some 700 to 1300 mm to meet its water requirements (ETm). In the early vegetative penod, crop water requirements are low, or some 10 percent of total. They are high dunng the flowenng period when leaf area is at its maximum, or some 50 to 60 percent of total. Later in the growing period the requirements decline. In relation to reference evapotranspiration (ETo) the crop coefficient (kc) for the different development stages is: for the initial stage 0 .4-0,5 (20 to 30 days), the development stage 0 , 7-0.8 (40 to 50 days), the mid-season stage 1.05*1.25 ( 50 to 60 days), the late-season stage O.B- 0.9 ( io to 55 days), and at harvest 0.65-0. 7.

WATER SUPPLY AND CROP YIELD

The crop growth penods for cotton arc shown in 1 ^gurc . i he r c ia t u s in p » between relative yield decrease and relative evapotranspiration deficit are shown in Figure 15. For calculation examples see p. 40 and Chapter \

Adequate water supply is needed for vigorous growth, goou budding and iruittng and for the formation of healthy bolls. Excess water early in tne growing period w ill restrict root and crop development. Cotton requires adequate water supply particularly just prior and during bud formation (2a). Continued water supply dunng flower opening (2b) and yield formation periods results in prolonged and excessive growth and yield. Abrupt changes in water supply will adversely affect growth and cause flower and boll shedding. Severe water deficits dunng flowenng may fully halt growth, but with subsequent water supply crop growth recovers and flower formation ts resumed.

When th« gtx>wmg s«a»on i « short such conditions lead to smaller y ie ld . Water stress on conoa can be observed by discolouring of the stem and appearance o f a bluish- green colour on the leaves.

ill.cite

F ig . 15 * Relationship between rela tive yield decrease Cl - Ya/Ym)nr i l r e l a r ^ v f * c v a p o t n n ^ p i r a T t o n ’ - F T a ^ F T m ' ) f p r c c T t o n

Water supply for high production must be adjusted to the specific requirements o f aach growth p e n ^ (see Scheduling). Optimum use o f available water supply can be ina ia by fully wetting the entire root ^onc up to I .80 m at sowing and with subsequent wettmg o f me upper part (0.50 to 1 m) o f the root /.one only. Root activity may be mcreased and full utilization o f the available soil water over the entire root zone is made with little o r no soil water le ft at the end of the growing season. Other savings can b« made by utilizing the available water m the entire root depth by timely discontinuing irrigation aBpUcatlons at the end o f the total growing period. A lso savings can be achieved by withnolding supply during the flowering period (2 ) until some 70 percent o f the total available soil water has been taken jp by the crop. A combination o f the above practices may save up to 20 percent water without greatly impairing y ie lds.

Ai sowing, mlequatc soil water should be available for germination and establishment (0 ). During the vegetative period (1 ), soil water content over the root depth o f some 0.75 m should not fa ll below SO percent depletion; greater depletion of available so il water (up to 75 percent) snll re s tric t vegetative growth but when followed by staple supply, vegetative growth w ill be somewhat excessive, which may cause late f lc eas ing , boll shedding and reduced yield when the growing season is short. At f l e e r in g <2), supply w ill need to be scheduled to control vegetative growth in relation to productive grow th. Water defic its from onset o f flowering to peak flowering may cmiae a auire negative e ffect on yie ld as compared to when occurring after peak flow ering• W ith severe w ater d e fic its durmg la ta flow ering and ea r ly boll formation, boll shedding can be aacaastve. M oderate w ater d e fic it occurring during now enng (2 ) but highenoug6 to re a trtc t vegetative grow th. w<Tl to goo<' p ile a raductioo m niosbcr of Aower'

Yields, des-

w ater supply should be available during the yield formation period U ). er holding capac . it. development o f the root system and

91

evaporative demand, the water supply during the yield formation period (3 ) should be discontinued at a certain time before the npening penod (4). Excessive water supplv dunng the yield formation period ( 3) may cause delay in boll opening and greater susceptibility to lodging and boll-rot. Under conditions of a long and warm growing season, an irrigation after the first harvest is sometimes practised to obtain a second yield.

When water supply is limited, a higher total production is obtained by extending the area and partially meeting crop water requirrmi'nts n th .'r t*t hiUcrop water requirements over a limited area.

WATER UPTAKE

From emergence to early flowering, the lap root may extend in deep soils to a depth of 1,8 m. During the flowering period , additional root development occurs in the upper part of the root zone. Frequent, light irrigation application during ea r ly growth periods tends to cause shallow root systems. As a rule, some 70 to 80 percent of the total water uptake by the crop occurs over the first 0.9 m depth, where more than 90 percent of the total root weight is found. Normally when the crop is fullv grown, 100 percent of the water is extracted from the first 1.6 to 1.7 m soil depth CD - 1 .0- 1,7 m). When water supply is terminated, water uptake will increasingly occur from lower soil depths but may not be sufficient during peak water requirement periods to maintain crop evapotranspiration and crop growth. Under conditions when ETm is 5 to 6 mm/day water uptake starts to be reduced when soil water depletion exceeds 65 percent ( p •0.65).

I R R I G A T I O N S C H E D U L I N G

lo enhance root development, adequate water should he available in the soil at the lime of sowing and pre-irrigation is required when stored soil water from pre- season rainfall is not available. In the vegetative period ( 1) irrigation may be scheduled when some 60 percent of the available sou water over the first 0.75 m has been taken up by the crop. During flowering (2) depletion of some 70 percent of available soil water will in general check vegetative growth without impairing yields; delayed irrigation during this period may cause considerable flower and bud shedding. During yield formation (boll filling) (3) and ripening (4), the soil water depletion may increase from 60 percent to higher values as the season progresses and depending on climate and

of stored soil water, irrigation can be terminated 4 to 5 weHts before final picking.

When grown under conditions of high groundwater tables, even for short duration, and when soils are wet for long periods, the yield decrease may be up to 50 percent, not withstanding unrestricted water use. This may be due to inadequate soil aeration.The same phenomenum has been noticed under very frequent irrigation application.

i r r i g a t i o n m e t h o d s

Cotton IS grown under a great variety of irrigation systems of which furrow irrigation is the most common surface system. In regions where the demand for water is great and water resources are small, sprinkler and drip irrigation methods become more and more accepted to economize on water applied and restrict return flow of low quality.

In the Near East region, cotton is also grown under controlled flood or spate irrigation, where with little or no rain a one-timc pre-sowing irrigation of 0 .5 to I n depth stores su/hcient water m the root zone to allow the crop to reach maturity. Under such treatments soils must be deep and have a high water holding capacity.With growing season from August to March with ETm - 700 to 750 mm and ETa ■ about ^50 mm, farmers’ yields arc about 800 kg/ha, with a maximum of about 1 700 kg/ha seed cotton.

92

YIELD*AND QUAl ITY

A goou yield oi a itxj lo day co t ton crop under irrigation is ^ to 5 ton/ha seed cotton of which 35 percent is lint. Water utilization efficiency for harvested yield (Ey ) for seed cotton containing about 10 percent moisture is 0.^ to 0.6 kg/m3.Boll and fibre properties such as lint to seed ratio, and length, strength and fineness of Unt, are primarily determined by the variety and to a lesser extent by irrigation and fertil izer practices. In general, the boll size, and the seed and lint index (weight per 100 seeds) increases under adequate water supply. However, the hnt percentage (the ratio lint to seed) tends to decrease. Low soil water depletion levels during yield formation (3) tend to result in longer and finer fibre of decreased strength. The direct effect of water deficits on fibre properties, however, appears to be small because of the shedding of bolls which would have produced inferior fibre when allowed to mature.

Normally cotton seed contains 35 percent oil and 35 percent protein. Under irrigation there is an indication that severe water deficits substantially reduce the oil percentage in the seed, and more fibrous material with 20 percent lower oil and protein content is produced compared to an adequately irrigated crop.

GRAPE

Grape is believed to originate froin the Caspian and Caucasian regions. Most cultivated vines belong to the European type (Vitis v inefera). the American bunch

Cy * labrusca and its derivatives) o r Muscadine type rotundifoha). Of the total production, 10 percent is eaten as fresh fruit, 10 percent is used for raisin production (annual production about 1. 1 million tAns) and 80 percent for wine p ro duction (annual production about 31 million tons of wine).

Grape is grown between about 50^N and S , with suitable areas being small at these limits. The crop needs a long, warm to hot, dry summer and a cool winter.The subtropics with winter ram are most suited. Rain or cold and cloudy weather during flowering may adversely affect fruit setting whereas rain during ripening may lead to fruit rot. Where raisins are produced by sun-drying between the vine rows, at least one warm, sunny month without ram following harvest is essential.

In climates with a cool winter, the grape can survive temperatures down to - 18®C , but once new growth begins, minor frost will kill the fruiting shoots. Rapid and succulent growth of shoots starts when mean daily temperatures reach 10®C, During flowering the rate of shoot growth declines and stops when the grapes arc mature. The time from flowering to maturity can be expressed as the sum of mean daily temperature above 10®C or 3 (T - 10°C), which is about 900 degree-days for early varieties and 2 000 for late varieties. Under cool to moderate warm weather, fruits ripen slowly and produce dry table wines of good quality. In warmer climates, the heat before and during ripening favours a high sugar content, which makes fruits better suited for port and sherry production. During and after harvest no new shoot growth should take place but leaves should be retained. In the autumn shoots, then also called canes, become woody and lose their leaves.

In the tropics (with less than 1 percent of the world production), the vine i » an evergreen and can produce fresh fruits throughout the year. In general, two harvests of re lative ly poor quality and low yields are obtained annually with harvest dates controlled by adjusting the time of pruning.

Grapes are adapted to a wide range of so ils , except when poorly drained or when salt content is high, in general, light soils are preferred. High production con be obtained under ramfed conditions, but without summer rain a deep soil with a high water holding capacity is required. Under irrigation, grape con be grown successfully on shallow soils of 0 .6 m depth or less.

On deep, fertile soil, the largest vines and high yields are produced. On soils of low fertility or limited depth, yields are usually lower, but fruit quality can be better. Fert i l ize r requirements are 100 to l60 kg/ha N, ^ to 60 kg/ha P and 160 to 230 kg/ha K. The greatest amount of nitrogen is needed during early spring growth and during the flowering period. During ripening, the nitrogen level must be low to prevent continuous vegetative growth.

Grape vines are moderately sensitive to soil salinity and yield decrease is 0% at ECe 1*5 mmhos/cm, 10% at 2.5 , 23% at 1, 50% at 6.7 and 100% at 12 mmhos/cm.

Most grape varieties are propagated by cuttings, grown in a nursery for one year to produce roots. Where root louse is a problem, grape is grafted on resistant roo t-stocks. An important (and expensive) operation is the training, pruning and staking of the vines and thinning of clusters. In the tropics the lime of pruning determines the time of fruiting. 1 he plant spacing is also influenced by the pruning and I raining practices and can vary between 1*5 x 3.5 and 5 x 5 .5m .

The crop coeflicient (kc) w ill vary with cultural p ractices . The kc value, relating the maximum water requirements (ETm ) to the re ference evapotranspiration (E T o ) , for clean cultivated conditions, infrequent irr igation and a dry soil surface most o f the time is ;

I a n F «b Mar Apr May lune 1\ii Aug Sept Oct Nov Dec

Mature grapevines grown in areas with k illing fros t ; initial leaves ear ly M ay, harvest mid-September; ground cover 40-30% at mid-season

- . 4 5 - 0 >65-.73 .7 5 - .9 .8 - .9 5 .75 --9 -65-.75 -

Mature grapevines in areas with light frost ; initial leaves ear ly A p r i l , harvest late August to ear ly September; ground cover 30-35% at mid-season

- .4 5 -0 .55--b5 .6 - ,75 .6 - .7 5 .6 - .75 .6 - .75 o - . 6 5 .35 - .4 -

Mature grapevines grown in hot, d ry areas and mild winter; initial leaves lato February - early M arch, harvest late July; ground cover 30-35% at mid-season

.25 .45 .6 - .6 5 -7 -.75 .7 - .75 . 6 5 - . ? .55 .45 .35

Total seasonal requirements vary between jOO and 1 20U mm, depending mainly on climate and length o f growing pen od .

w a t e r ^ 'Vt <

W ATER S U P P L Y AND CROP Y IE LD

Grape is a perennial crop and can adjust to a certain extent to limited water supply by developing a deep root system. When soil water even o ve r great soil depth becomes limited and ovem igh i recovery from wilting does not occur, growth will diminish and eventually stop. Subsequently leaf and shoot colour change to a dark greyi sh - g re en , the shoot tips become d ry , the leaves curl, the tendrils abscise and eventually the leaves die and fa l l .

In the subtropics and temperate climates, flowerbud formation generally occurs d u n a g the late summer or autumn and the buds open during the next season. A slight d e fio e n c y o f water, together with high sunshine and temperatures, is considered to be ■M a t to vm trab lc to Row er bud fo rm a tio n . A dry summer and a re la t ive ly low yield appears to Lo •' r. * 'vantageou'- Power bud formation than a wet summer and a heavy yie ld

For good fruit production in the same year and the following yea rs , good wcgtftative growth during the first part o f the growing period (vegetative period , 1) la important. Water deficit should not occur during this penod of rapid lateral shoot-

Sw w th. The a o ii w a te r coo lcn t ahould preferab ly be at field capacity at the end of e w in te r , by w in te r ra in o r by irr igation , to ensure adequate water supply during

the f i r s t months of the growing period. Especially shoot elongation ts very sensitive to w a te r d e f ic its . Adequately irrigated vines have significantly more prunings than those grow n under w a te r d e f ic it conditions. If water stress occurs abruptly, the grow th IS checked and wilting and dieback occur; if water stress develops gradually the vgae gr owth is adjusted ^ lessened shoot growth, smaller production and ea r l ie r r i p af g. H ow ever, vegetative growth should be low during fruit formation and should •top tow ard harvest to ensure good npening o f the fruit and maturing of the wood.

P r io r and durtag nowertng (2 ), adequate water supply is necessary for flower deve!opment. Water Jefttit^ at this time re»ar^ n ev e r d i*v eL'i;™*-', r while severe

93

defic it reduces fruit set. A lso the nutrition requirements o f the grapevine a re high during this penod and the subsequent fruit enlargement period . Leaching o f nutnenis must be avoided in this per iod .

Y ie ld formation (fruit enlargement, 3) depends on a steady, continuous water supply, but in this period the crop is less sensitive to water defic its than during the penod of shoot growth (1). W ater defic its during friiit enlargement reduce fruit s ire . Later irr igation does not result in undersized fruits becoming normal s ize . W ater defic its p r io r to o r just after v^raison (start o f ripening, fruits soften and change co lour) affect fruit s ize more than defic its just before harvest.

S evere water defic it causes shnvelltng o f the fruits at a l l stages o f yield formation (3 ) and ripening ( i ) and is first observed in the immature fruits on any cluster. The shrive lling usually disappears a fter rewatenng. Complete desiccation IS confined to the smaller fruits ( less than about L mm in diameter). When ihe crop is subjected to severe water defic its after vdraison, maturity is delayed while the fruits may not even reach full maturity. A slight water defic it during the ripening period ( i ) may hasten maturity, while juice concentration is increased.

Water defic its throughout the growing season result in darker wine but may not affect the quality o f the wine. S evere water defic it during yield formation (3 ) and ripening (^ ) results in the fruit having a dull colour. It also leads to sunburn but reduces the incidence of fruit ro t. S evere defic its just a fter v^raison reduce theO’ lof't o f total soiublc solids.

A fte r the fruit is mature and especia lly after harvest, the vines become adjusted to a limited water supply. Normally no further growth occurs , but leaves are retained and canes ripen even though soil water content is low. In hot, dry reg ions, water deficit after harvest will cause the leaves to fa ll; when weather becomes cool in autumn, new leaves can be formed without becoming mature. This will lead to poor p ro duction in the next year. Water supply after harvest must therefore be sufficient to maintain the healthy foliage and to prevent premature lea ffa ll . H owever, too much water after harvest causes new shoot growth, which has the same detrimental effects as new lea f growth. The relation between re lative yield decrease and re la tive evapotranspiration defic it IS given for conditions when soil water stress occurs mainly in the second part o f the total growing period , and water supply during early vegetative growth (1) and the flowering period (2 ) is adequate (H ig. l6 ). To maximize tota l p r o duction i f water supply is limited the cultivated area may be extended and crop water requirements partially met, rather than meeting full crop water requirements on a limited a r e a .

W ATER U PTA K E

When root penetration is not obstructed, mature grapevines are deep rooted up to depths o f 2 o r 3 m, o r more. In deep, coarse sand or grave lly so ils , roots mgy be up to ^ to 8 m deep. The bulk of the roots are usually in the upper soil layer of 0 .5 to 1.5 m. Normally 100 percent of the water is extracted from the first 1 to 2 m soil depth CD • 1-2 m). During vegetative growth (1 ), flowering (2 ) and the early pari of yield formation (ea r ly 3) maximum evapotranspiration w ill he affected at a soil water depletion (p) o f about 0 ,35 to O.AS, under conditions when ETm is 5 to 6 mm/day- Later in the growing penod the soil water can be depleted to a higher le v e l , while

and after * i^^ter depletion is required.I r


When winter rainfall is in^ irrigation shoub’ ^ e r 'r '

to fi l l the full root zone to field capacity.c r V n T i l W gir '-m c cf the

' - smsLO 0» 00 07 Oft 03 04 03 02 Oi 0

F i g , 16

Relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ ETm) for grape

v4raison water must be applied when 35 to ^5 percent of the total available soil water IS depleted. Whether irrigation is necessary after vdraison depends on the total available water over the root depth in relation ;o ETm. In shallow and light soils , irrigation will be necessary until harvest, but be applied at higher soil water depletion levels (so il water potential between I and 5 bacs).

In deep, fine textured soils irrigation should be discontinued in time to achieve the desired soil water depletion level toward harvest time. In warm, dry climates or when the grapes are harvested ear ly , a light irrigation may, however, be required to prevent tba soil from becoming too dry (water potential not exceeding 3 to 10 bars).

When sprinkler irrigation is practised, after v6raison irrigation should not take place during humid periods in o i^ e r to assure rapid drying of the leaves (6 to 12 hours), and to reduce fo liar bum and the hazard of fruit rot.

IRRIGATION METHODS

Furrow irrigation with 2 or 3 furrows between the rows is mostly used. Sprinkler irrigation becomes more common since it can also be used for spring frost protection where needed. Sprinkler is less advantageous when irrigation is also roqulred during the npcmng pexnod because of the likely increase in bunch rot. In new vineyards and especially where irrigation water is scarce, drip irrigation is I n " r'*.*' " J ; T 1 ■ .

Y I E L D

Similarly to other perennial crops, yield per vine vanes considerably from year lo year and from plant to plant. The maximum yield level depends on the variety and growing environment. Good commercial yields in the subtropics are in the range o l I d to 20 kg grapes per vine or IS to 30 (o r more) tons/ha (80 to 85 percent moisture). Ytalds in the tropics arc m the range of 5 to 10 ton/ha. The water utilization •fhciancy for hanrested yield (Ey ) for fresh fruits containing about 80 percent mois- t v r t K 2 to ^ kg/»^ when grape is grown in the subtropics.

GROUNDNUT

Groundnut ( A rach is hvpogaea) orig inates from South Am erica. Presen t annual world production of unsheUed nuts is about 18,5 million tons from about 19.3 million ha.

The crop is grown between 4 0 ^ and S latitudes. Its growing penod is 90 to 115 days for the sequential, branched v a n e t ie s and 120 to 140 days for the a l t e r nately branched va r ie t ie s . The mean daily temperature for optimum growth is 22 to 28®C; a reduction in yield occurs above 33®C and below 18®C. Germination is delayed at temperatures below 20®C. Groundnut is considered a day-neutral plant and daylengih is not a c r it ica l factor influencing y ie ld . F o r good y ie ld s , a rainfed crop requ ires about 500 to 700 mm o f re l iab le ra in fa ll o v e r the total grow ing per iod .

The crop is best adapted to w e ll-d ra in ed , loose , fr iab le medium textured so i ls . Heavy textures cause problems in lift ing the crop at harvest. A ls o , the lop soil should be loose to allow the pegs (on which the fruits are formed) to enter the soil eas ily .

Being a legume, groundnut can fix nitrogen from the a ir . H ow ever , a pre-p lanting nitrogen application of 10 to 20 kg/ha is often recommended to assure good crop establishment. P h os phorous requirements are 15 to 40 kg/ha; potassium requirements 25 to 40 kg/ha.A too high application o f potassium can cause a decrease in y ie ld . F or proper kernel formation and pod-fiU ing, 300 to 600 kg/ha o f calcium is require<i at the beginning o f pod formation in the top soil where the fruits are formed. Limestone IS used when soil acidity needs to be corrected and gypsum when only the Ca leve l needs to be increased. At pH low er than 6 , liming may be necessary to avoid aluminium and manganese toxic ity.

The crop is moderately sensitive to sa lin ity and y ie ld decrease for d i f f e r ent soil salinity leve ls is : 0% at ECe 3.2 mmhos/cm, 10% at 3. 5» 25% at 4 .1 , 30% at 4 .9 and 100% at ECe 6. 5 mmhos/cm.

The crop is planted at a row spacing o f between 0 .75 and 1.0 m c o r r e s ponding to a plant density ot about some 120000 plants/ha for the small podded v a n e t ie s and 70000 plants/ha for la rge podded va r ie t ie s . Seed rates are 30 to 50 kg/ha and 60 to ^ kg/ha for the two v a n e t ie s respect ive ly . When unshelled nuts are used for sowing, the pod^ are often pre-soaked to minimize damage (o the seed. At sowing the soil water content should p re ferab ly not be below 60 percent available soil water. F ig . 17 Groundnut durittR *

Crop rotaiion is recommended since groundnuts are able to abstract large •■KMints of nutrients from the soil and also to reduce infestation of root knot and lesion nematodes. Groundnut is genet ally preceeded by a crop requiring heavy fertil izer application such as maize. A 3 to 5 year rotation is preferred to a 2-year rotation.

W ATER R E Q U lR b M L M S

Depending on climate, the water requirements range from 500 to 700 mm for the total growing penod . As related to development stages, the kc value for the initial stage is 0 .4 -0 . 5 (15 to 35 days), the development stage 0, 7-0.8 (30 to 45 days), the mid-season stage 0.95-1* I (30 to 50 days), the late-season stage 0 .7 -0 .8 (20 to 30 days), and at harvest 0 .55 -0 .6 .

W ATER S U P P LY AND CROP YIELD

Vegetative and reproductive growth show a uolinite response to water supply However, excessive soil water is harmful because lack of oxygen in the soil limits the activity o f the N -fixm g bacteria; this is noted by an unhealthy growth pattern and yellowing o f the leaves. Excessive soil water in heavy soils at harvest can cause the pods to be tom easily from the pegs with the pods remaining in the soil.

The relationship between relative yield decrease and re lative evapotranspiration de fic it , based on interpreted information, is given in Figure 18. For calculation examples see p . 40 and Chapter V I .

f t f tto 0 * os o r OS 09 04 01 02 Oi 0 10 OS OS or OS OS 04 09 02 01 0

........................................... ^0

01O " '

02

OS

04 v>

■09

fOS

or

os

iM m m m n * r«4 os .MMM r*4

10

01

02

05

04

05

OS

or

OS

osI[0

Fig. 18 Relationship between re lative yield decrease (1 - Ya/Ym)and relative evapotranspiration deficit (1 • ETa/ETm) for

groundnut

0 establishment 10 - 20 day a1 vegetative 25 - 352 flowering 30 - ^03 yield formation (including pod setting and

pod filling) 30 - 35L ripening 10 . 20

Flowering continues during part of the yield formation period but the pods from the late-formed flowers do not reach maturity.

The flowering period (2) is most sensitive to water defic it, followed by the yield formation period (3 ), In general, water deficits during the vegetative period (1 ) cause delayed flowering and harvest, and reduced growth and yield. Water deficits during flowering (2) cause flower drop or impaired pollination, whereas water deficits durmg the y ie ld formation period (3) give a reduced pod weight. The early part of the yield formation period (pod setting) is particularly sensitive to water defic it. In the case of limited water supply, water savings should be made during the periods other than flowering ( 2 ) and early yield formation (3 ). A higher total p ro duction IS obtained by increasing the cultivated area and partially meeting crop water requirements rather than by meeting full crop water requirements over a limited area.

99

The growth periods for groundnut are:

W ATER U PTAKE

The crop has a w e l l-d eve loped tap root with many la tera ls which may extend to a depth o f l . o m. The major part o f the root system is , however, found m the firs t 0 .5 to 0 .6 m soil la yer . Full grown plants normally extract 100 percent o f the water from the f irs t 0 .5 to 1.0 m of the soil CD • 0. 5 -1 .0 ) . Under an evapotranspiration rate of 5 to 6 mm/day, the rate o f water uptake by the crop starts to reduce when some 50 percent o f the total available soil water has been depleted (p - 0 .5 ) .


Depending on the leve l o f crop evapotranspiration and water holding capacity o f the so il, in te rva ls vary from 6 to days up to 21 days for loam so ils , with shorter intervals during flowering (2 ) when depletion o f available soil water should not exceed ^0 percent. In the case o f supplemental ir r iga t ion , best results are obtained when water is applied during the flowering period ( 2 ) .

IRRIGATION METHODS

On light-textured so i ls , sprinkler irr igation o f fe rs advantages by light and frequent water application, sufficient to wet the f irs t 0 . 6 m o f the soil. Furrow irr iga t ion is frequently used on medium textured so ils .

YIELD AND QUALITY

UunshcUed

A N D Q U A L I T Y

Under ramfed conditions good average jnelds vary from 2 to 3 ton/ha k1 nuts under a high level of management. Under irrigation and a high level

100

of management, yields can be 3> 5 to ^ .5 ton/ha unshelled nuts. The water utilization efficiency for the harvested yield (Ey) for unshelled, dried nuts with a moisture content of about IS percent is 0.6 to 0.8 kg/m^. Groundnuts contain about 30 percent protein and are rich in vitamins B and C. The oil content for the Virginia bunch type (alternately branched), i s between 38 and L I percent; for the small seeded Spanish types (sequentially branched), L I to 50 percent. Oil content IS reduced considerably when water deficits occur during the yield formation period (3).

MAIZE

Maize (Zea Mays) originates in the Andean ragion of Central America. It is one of the most important cerea ls both for human and animal consumption and is grown for grain and forage. Present world production is about 335 million tons gram from about l i d million ha.

The crop is grown in climates ranging from temperate to tropic during the period when mean daily temperatures are above 15^C and f ro s i - f r ee . Adaptability o f variet ies in different climates van es widely. Successful cultivation markedly depends on the nght choice of varieties so that the length of growing period of the crop matches the length of the growing season and the purpose for which the crop is to be grown. Var iety selection trials to iden tifv the best su itable v a r ie t ie s fo r given a rea s a re frequently necessary.

When mean dai ly temperatures dunng the growing season arc greater than 20®C , early gram varieties lake 80 to 110 days and medium varieties 110 to 1^0 days to mature. When grown as a vegetable, these variet ies are 15 to 20 days shorter. When mean daily temperatures are below 20®C , there is an extension in days to maturity of 10 to 20 days for each 0 . decrease depending on variety , and at 15^C the maize cram crop takes 200 to 300 days to mature. With mean daily temperature o f 10 to 15 c maize vs mostly grown as a forage crop because of the problem of seed set and gram maturity under cool conditions. For germination the lowest mean daily temperature is about 10®C , with 18 to 20®C being optimum. The crop is very sensitive 10 f rost , particularly in the seedling stage but it tolerates hot and dry atmospheric conditions so long as sufficient water is available to the plant and temperatures are below ^5®C. Temperature requirements, expressed as sum of mean daily temperatures, for medium varieties are 2 500 to 3 000 degree d ays , while early variet ies require about 1000 and late varieties 3 700 or more degree days.

In respect o f daylength, maize is considered to be either a day-neutral or a short-day plant. The growth of maize is very responsive to radiation. However, f ive o r SIX leaves near and above the cob are the source of assimilation for grain fi ll ing and light must penetrate to these leaves. For optimum light interception, for gram production, the density index (number o f plants per ha/row spacing) vanes but on average it is about 150 for the large late varieties and about jOO for the small early variet ies. Sowing methods and spacing vary , and ferti l ity and water are dec is ive factors in choosing the optimuri density in relation to light interception and highest y ie lds. Plant population van es from 20 to 30000 plants per ha for the large late varieties to 50 to oOOOO for small e a r ly varieties. Spacing between rows vartea between 0 ,6 and 1 m. Sowing depth is 5 to 7 cm with one or more seeds per sowing point. When grown for forage, plant population is 50 percent higher.

The plant does well on most soils but less so on very heavy dense clay and very sandy soils. The soil should preferably be well-aerated and well-drained as the crop is susceptible to waterlogging. The ferti l ity demands for gram maize are re lat ive ly high and amount, for h i^-producing var iet ies, up to about 200 kg/ha N,50 to 00 kg/ha P and 60 to 100 k g ^ a K , In general the crop can be grown contmuovsly as long as soil fert i l ity is maintained.

Maize IS moderately sensitive to sahnity. Yield decrease under increasing soil salinity i s ; 0% at ECe 1.7 mmhos/cm, 10% at 2. 5» 25% At 3.0, 50% at 5*9 and 100% at ECe 10 mmhos/cm.

Maize 15 an efficient user of water in terms of total dry matter production and among cereals it is potentiallv the highest yielding gram crop. For maximum production a medium maturity grain crop requires between 500 and 800 mm of water depending on climate. To this, water losses during conveyance and application must be added. The crop factor Otc) relating water requirements (ETm; to reference evapotranspiration (E T o ; for different cr p growth stages o f gram maize is for the initial stage 0 .3 -0 .5 (1 5 to 30 d ays ), the development tage 0. 7-0.85 (30 to LS days) the mid - season stage 1.05-1 • 2 (30 to ^5 days), during the late season stage 0 .8 -0 .9 (10 to 30 days), and at harvest 0. 55-0.6.

102

W A T E R R E Q U I R E M E N T S

W ATER S U P PLY AND CROP YIELD

The growth periods of maize are shown in Figure 19- The relationships between relative yield decrease (1 . Ya/Ym) and relative evapotranspiration deficit are shown in Figure 20. For calculation examples see p. LO and Chapter V I,

Frequency and depth of irrigation and ram has a pronounced effect on gram yield. Maize appears re lative ly tolerant to water deficits during the vegetative (1) and ripening (L ) periods. Greatest decrease m gram >Telds is caused by water deficits during the flowering period (2) including tassellmg and silking and pollination, due mainly to a reduction in gram number per cob. This effect is less p ro nounced when in the preceedmg vegetative period (1) the plant has suffered water defic its . Severe water deficits during the flowering period (2 ), particularly at the time of silking and pollination, may result m little or no grain yield due to silk drying. Water deficits during the yield formation period (3) may lead to reduced yield due to a reduction in gram size . Water deficit during the ripenmg period (L ) has little effect on gram yield.

The effect o f limited water on maize gram yield is considerable and careful control of frequency and depth o f irrigation is required to optimize yie lds under conditions of water shortage. Where water supply is limited it may therefore be advant ageous to meet, as far as possible, full water requirements (ETm) so as to achieve near maximum yield from a limited acreage rather than to spread the limited water over a la rger acreage.

M aize flourishes on well-drained soils and waterlogging should be avoided, particularly during the flowering (2) and yield formation (3) periods. Waterlogging during flowering (2 ) can reduce gram yields by 50 percent or more.

WATFR UPTAKE

When evaporative conditions correspond to ETm of 5 to 6 mm/day, soil w a ter depletion up to about 55 percent of available soil water (Sa ) has a small effect on yield (p - 0,55). To enhance rapid and deep root growth a somewhat greater depletion during early growth periods can be advantageous. Depletion of 80 percent or more may be a l lo w ^ during the npening period.

Although m deep soils the roots may reach a depth of 2 m,the highly branched e y e tM is located m the upper 0.0 to 1 m and about 80 percent of the soil wateruptake occurs fro m this depth. Normally 100 percent of the water is taken up from the first I to 1. 7 « soil depth CD - 1 t o 1.7 m). Depth and rrate of root growth is , however.

103

■mec

Istakitahmvni iO>

It - St eay*

F ig . 19 Growing per iods of maize (a f te r Hanway, 1966)

i-taU rn

10 09 OS or OS 05 04 03 01 01 0

Fig* 20 RelaiioiibUip Lotwcou re la t ive y ie ld decrease (1 - Ya/Ym) and re la t ive evapotranspiration def ic it (1 - ETa/ETm) for maize

1 0 4

greatly affected by rainfall pattern and irrigation practices adapted. In addition to soil water and nutrient status, root development is strongly influenced by textural and structural stratification, salts and water tab le.


To obtain a good stand and rapid root development, the root zone should, where feasib le, be wetted at or soon after sowing. Taking into account the leve l o f ETm, to meet full water requirements, the water depletion leve l is about 40 percent in the establishment penod (0 ), between 55 and 65 percent dunng penods 1, 2 and 3, and up to 80 percent dunng the npening penod (4).

Where ra in fa ll is low and irrigation water supply is restr icted , irrigation scheduling should be based on avoiding water deficits during the flowering period (2) followed by yield formation period (3)- When a severe water deficit during the flowering period (2) is unavoidable, water may be saved by reducing supply during the vegetative penod (1) as w e l l as during the y ie ld formation penod (3) without ticurnng additional y ie ld losses.

Under conditions of marginal rainfall and limited irrigation water supply, the number of piossible irngation applications may vary between 2 and 5* A su gges t^ timing of these irrigation applications is given below. To obtain a good stand and proper Voot development, the potential root zone :>hould be wet either from rainfall o r irrigation p r io r or soon after sowing.

No. o f Establish- Vegetative Flowering Y ie ld Ripeningirrigations ment formation

(0) (1) (2) (3) (4)

234

5

YIELD

Under irrigation a good commercial grain yield is 6 to 9 ton/ha (10 to 11 cent moisture). The water utilization efficiency for harvested yield (P v l P « r -vanes then between 0.8 and 1.6 kg/m^. firain

OLIVE

O l iv e (O lea europacal ) probably originated from the Eastern Mediterranean reg ion o f the Middle East. P resen t production is about 8 .5 « i i l l i o n tons green and black table o l iv es and 1.6 miUion tons o i l . Of the total production, 95 percent is produced in the Mediterranean reg ion with Spam and Italy being the main producing countr ies.

The crop is indigenous to the Mediterranean region with a mild, ramy winter and a hot, dry summer. A dormancy per iod of about two months with average tempera tures low er than lO^C is condusive to f lower bud d if ferentia t ion. Some cult ivars are adapted to areas with higher winter temperatures but reduced f lower ing is noted under these conditions. During the dormancy pe r iod , the t ree to lera tes short pe r iods o f frost o f -6®C, but during the bearing period frost causes damage to the fruits which arc then only suitable for oi l production. High temperatures and dry winds cause poor fruit setting and ex cess iv e drop o f young fruits with remaining fruits shr ive l l ing on the t r e e . A long, sunny, warm summer results in a high oi I content o f the fruit . High humidity at f l o w e r in g causes f low er drop and infestation o f sooty mould.

The crop produces acceptable y ie lds on poor soil as long as it is deep , w e l l - aerated and free from water logg ing. Under water logged conditions damage through lack o f oxygen and fungal d iseases increases sharply. The f e r t i l i z e r requirements a rc 200 to 250 kg/ha N , 55 to 70 kg/ha P and l60 to 210 kg/ha K , N itrogen is applied p r i o r to o r during the f lower ing and fruit formation period*

The o l i v e t r e e is moderately tolerant to soil salinity provided ECe does not exceed 8 mmhos/ cm , but ECc o f 5 mm ho s/cm o r less is p r e f e r r e d .

Raised fo r two y ea rs in the nursery , the t re e is transplanted ear ly in the season with 15 to 20 trees/ha under poor ramfed conditions and up to 300 trees/ha under i r r iga ted conditions. T r e e density is also dependent on the method o f pruning. Early pruning is not essential but is often pract ised to obtain strong stems. H ow ever , f o r o lder t r e e s , pruning during w inter is necessary for high y ie lds . Intercropping with grain forage and vegetable crops is sometimes pract ised in young orchards but IS discontinued a fter 15 to 20 years under ramfed and after 6 yea rs under i r r iga t ion .

M o re fruits are set than can be supported by sufficient nutrient supply, and this tendency increases as the t rees get o lder . Consequently, a small number o f f lowers produce fruits . Early f low er drop can be attributed to inadequate poll ination, nutrient de f ic ienc ies o r water shortage. Late f low er and f m i i drop is caused mainly by o l ive moth and ohve fly attacks and water shortage. On the other hand, abundant fruit ing adverse ly a ffects growth of annual shoots and the next y ea r crop snd eventually leads to alternate fruit bearing. This tendency is g rea te r in o ld er trees but alternate bearing is less pronounced with good soil and climate, and adequate management pract ices . The economic l i fe o f a t ree is 50 years under ramfed conditions but under favourable growing conditions it can be much longer. A prof itable harves t 19 obtained a fter 6 yea rs but under more extreme conditions, a f ter 15 to 20 years .

WATER REQUIREM ENTS

Ohve trees a re commonly grown without irrigation in a reas with an awiual rain fall of ^00 to 6OO mm but are even found in areas with about 200 mm rain fa ll. For

[06

high yields, 600 to 800 mm are required. The crop coefficient Otc) relating maximum evapotranspiration (ETm) to reference evapotranspiration (E To ) is between 0.^ and 0.6.

WATER SU PPLY AND CRO P Y IE L D

The annual growth cycle of the olive tree in the subtropics with winter rain, together with the timing of cultivation practices, is shown in Figure 21.

Asr May Jim Jul Aug Sspt Oct Nov Dtc Jon— * * ^ ♦ rT- j-------.-------(-------1--------------

Acttvo wgttottvo qrcwth

Riducod vog. gniwth

Acfivo vta RMtIng / Dormant

m Flowwing(2) Yitid formation (3)

Stonobordng. Colooring

Rlponlng(4)

Vtrnolixation

Criticol fw Criticol forNltrogsn wotwesficit Pruning

(*)(«) Irrlgotion If noodad

(•) Horvtsting

F ig . 21 Annual growth cycle for olive m the subtropics in the northernhemisphere with winter ram (^fter Pansoit and Rcl>oiir. 1961)

In the subtropics with winter ram, adequate soil water is generally available u n t i l the ta le r part of the summer. For high yields, adequate water is required from the a ta r i of the stone hardening onward until the end of yield formation (3). During the yield formation period (3) adequate water supply increases fruit size and the f le t h / p i t ratio but the ripening period ( i.) is prolonged and the colouring of the fruit IS delayed. Table o lives, with a high flesh/pit ratio, require more water during the yield formation period (3) than olives produced for oil. In subtropical climates with little winter ram, water supply is also needed pr ior to flowering (2). Water deficits during the flowering period (2) may result in increased flower and fruit drop. Where needed, irrigation prior to the start o f flowering is recommended because irrigation d u r in g the flowormg period (2 ) may lend to leaching of the essential supply of soil n itro g e n .

Y ie ld s a re strongly a ffe c te d by twig growth during spring and e a r ly summer (from April to June in the northern hemisphere) and adequate water should be ava ila b le d u r in g this lime. This applies also to the wi nter period because water deficits in w in te r cause re d uce d tw ig growth and defoliation. Further, this also causes a la rg e p e rce n ta g e o f im p e rfe c t flowers during spring while retarding flowering.

A dequa te w a te r su pp ly d u r in g the a c tiv e growth p e r io d s tends to re d uce a lte rn a te b e a rin g c y c le s , w a te r d c f ic i ta m the s p r in g a d v e rs e ly affect lead d e v e lo p ment and a c tiv e g ro w th , c a u s in g a re d u c tio n in yield during the same vear and possibly

107

also the next. When the crop is grown fully under ir r iga t ion , application o f water could be discontinued only during the period between start o f f low er in g and the beginning of stone hardening.

Excess water results in short tw igs , dense fo l ia g e with short and narrow leaves and reduced y ie lds .

Under conditions o f limited water supply, overa l l production is increased by extending the area and part ia l ly meeting crop water requirements, rather than by meeting full crop water requirements o v e r a limited area .

W A T E R U P T A K E

A f te r 3 to 4 y ea rs the t ree forms a fasc i la r root system which continues to grow with age. In heavy textured and poor ly aerated so i ls , roots a re concentrated near the soil surface but are found at a g rea te r depth in light textured so i ls .La tera l r o o t s can be up to 12 m long. The tree thus exp lo re s a la rge volume of soil f o r nutrients and water . Genera l ly , water uptake occurs o ve r the f irst 1. 2 to 1.7 m o f soil depth G) - 1.2 to 1.7 m). Under conditions when maximum evapotranspiration (ETm ) IS 5 to 6 mm/day, the rate of soil water uptake by the crop starts to r ^ u c e when some 60 to 70 percent of the total available «.oil water has been depleted.


With winter ram o f about 500 mm, irr igat ion is applied during and after stone hardening. Under conditions o f htt le winter ram , irr igat ion is applied dunng bud dif ferentiat ion (ea r ly spr ing) , p r io r to f lowering ( e a r l y summer) and dunng y ie ld formation and part icular ly during stone hardening. Irr igation is also applied at (a ) two to three weeks before f lower ing; (b) when the fruit reaches one third Its full s i z e ; and ( c ) when the fruit reaches almost full s iz e .

For oil production, i r r igat ion supply must be discontinued ea r ly enough ro g ive a dry period during ripening. This will have l i tt le ef fect on the oil content but w i l l reduce the water content o f the fruit.

Irr igat ion is applied by dif ferent surface methods, but when l i m i i e u w a t e r is ava i lab le , local ized irr igat ion is p r e fe r r ed .

Y IE L D AND Q U A L IT Y

The fruits o f irr igated t rees reach a high oi l content later in the season than those o f rainfed t rees . A ls o , for irr igated trees the change of fruit colour from green to black is more gradual. O il content as percentage of fresh fruit weight tends to be higher for ramfed than for irr igated t rees but httle d i f fe rence is noted with oil content expressed as percentage o f dry matter.

Time of picking depends on the use of the harvested product. Var ie t ies with fruits o f a high flesh/pit rat io and uniform shape are used for table o l ive production. In the northern hemisphere, green table ohves are harves ted from mid-September onward with end of harvest being determined when the fruit colour changes to green- ye l low . Black table o l ives are harvested in December. O l ives fo r oi l a re harvested from mid-December until March with oil content independent of the time o f harvest.

1 0 8

Maximum oil content and weight are reached six to eight months after flowering. O live fruits can be harvested long before they fall naturally.

Yields vary from year to year and from tree to tree . Good c'^mmercial yie lds under irrigation are 50 to 65 kg/trce o f fruit with a possible maximum of 100 kg/iree of fruit. Oil content o f the fresh fruit ranges from 20 to 25 percent. The water utilization efficiency for harvested yield (Ey ) fo r fresh o lives containing about 30 percent moisture Is 1.5 to 2.0 kg/m^.

ONION

Onion (Allium cgpa) is believed to have originated in the Near East. The crop can be grown under a wide range o f climates from temperate to trop ica l. Present world production is about 16 million tons o f bulbs from 1.5 million ha.

Under normal conditions onion forms a bulb in the first season of growtri and f low ers in the second season. The production o f the bulb is controlled by daylength and the c r it ica l daylength var ies from 11 to 16 hours depending on varie ty . The crop flourishes in mild climates without extremes in temperature and without excess ive

rainfall* Fo r the initial growth p en od , cool weather and adequate water is advantageous for proper crop establishment, whereas during npen ing , warm, dry weather is beneficial for high yield o f good quality. The optimum mean daily temperature varies between 15 and 20^C . P rop e r crop varie ty selection is essentia l, particu larly in relation to the daylength requ ire ments; fo r example, a long day temperate va r ie ty in tropical zones with short days will produce vegetative growth only without forming the bulb. The length of the growing period va r ie s with climate but in general IJO to 175 days are required from sowing to harvest.

The crop is usually sown in the nursery and transplanted a fter 30 to 35 days. D irect seeding in the field is also practised. The crop is usually planted in rows or on raised beds, with two o r more rows in a bed, with spacing of 0 .3 to 0 .5 X 0-05 to 0.1 m. Optimum soil temp - erature for germination is 15 to 25°C. For bulb production the plant should not f lower since flowering adverse ly affects y ie lds . Bulbs are harvesteS when the tops fa ll: For initiation offlowering, low temperatures ( low er than 14 to 16*^C) and low humidity are required. F lowering IS, however, little affected by daylength.

Onion can be grown on many soils but medium textured soils are p re fe rred . Optimum pH 15 in the range of 6 to 7. F e r t i l iz e r requ ire ments are normally 60 to ICX) kg/ha N , 25 to 45 kg/ha P and 45 to 80 kg/ha X .

The crop i t sensitive to soil sa lin ity and yield decrease at va ry ing leve ls o f ECe is :0% at ECe 1.2 mmhos/cm, 10% at 1.8, 23% at 2 .8 , 50% at 4 .3 and 100% at ECe 7. 5 mmhos/cm.

Fig. 22 Onion during y ie ld fonnaUonpenod (3)

no

W A T E R R E Q U I R E M E N T S

For optimum yie ld , onion requires 350 to 550 mm water. The crop coefficient (kc) relating reference evapotranspiration (E To ) to water requirements (ETm ) for different development stages after transplanting is , fo r the initial stage 0 .4 -0 -6 (15 to 20 days), the crop development stage 0 .7 -0 .8 (25 to 35 days), the mid- season stage 0-95-1* 1 (25 to 45 days), the late-season stage 0 .85 -0 ,9 (35 to 45 days), and at harvest 0 ,75-0.85.

WATER S U P PLY AND CROP YIELD

Onion, in common with most vegetable crops, is sensitive to water deficit. For high y ie ld , soil water depletion should not exceed 25 percent of available soil water. When the soil is kept re la tive ly wet, root growth is reduced and this favours bulb enlargement. Irrigation should be discontinued as the crop approaches maturity to allow the lops to desiccate, and also to prevent a second flush of root growth.

The growth per iods of an onion crop with a growing period of 100 to 140 days in the field a re : establishment penod (from sowing to transplanting, 0) 30 to 35 days; vegetative penod ( I ) 25 to 30 days; yield formation (bulb enlargement, 3) 50 to 80 days and npening period (4) 25 to 30 days.

The relationships between relative yield decrease ( I - Ya/Ym) and re la t iv e evapotranspiration deficit ( I - ETa/ETm) are shown in Figure 23. For examples sec p. 40 and Chapter VI.

HII V U V W O r O O O S O X O f E M O l (

/ / '

' W \

0

01

02

05

04

05

(M

u U9 ua or 03 a« 4 02 Qi 0

“• v'XV

X '

X

W

t OS ' 1

0«

10

rm m

10

Fig, 23 Relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ETm) for

onion

The crop ts most sensitive to water deficit dunng the yield formation period (3 ) « particularly dunng the penod of rapid bulb growth which occurs about 60 days_ A _ ^ . 1___ ^ ^ __________ A A A wn H M a K M 1 C m m k k aa llt^ tranmlaniing. The crop is equally sensitive dunng transplantation. For a seed c fop , the flowenng penod is very sensitive to water deficit. Dunng the vegetativegrowth period (1) the ^rop appears to be relatively less sensitive to water deficits.

I l l

For high yield of good quality the crop needs a controlled and frequent supply o f water throughout the total growing period; howeVer, o v e r - im g a i io n leads to reduced growth.

To achieve large bulb size and high bulb weight, water de f ic its , especially during the yield formation period (bulb enlargement, 3), should be avoided. Under limited water supply small water savings can be made during the vegetative period (1) and the ripening period (^), However, under such conditions water supply should preferably be directed toward maximizing production per hectare rather than extending the cuhivnTed area with limited water supplv.

WATER UPTAKE

The crop has a shallow root system with roots concentrated in the u p p e r 0.3 m soil depth. In general 100 percent of the water uptake occurs in the first 0.3 to 0 .5 m soil depth (D - 0 .3 -0 . 5 m). To meet full crop water requirements (ETm) the soil should be kept relatively moist; under an evapotranspiration rate of 3 to 6 mm/day, the rate of water uptake starts to reduce when about 23 percent of the total available soil water has been depleted (p ' 0.25).


The crop requires frequent, light irrigations which are timed when about 25 percent of available water m the first 0.3 m soil depth has been depicted by the crop. Irrigation application every 2 to A days is commonly practised. Over-irrigation sometimes causes spreading of diseases such as mildew and white rot. Irrigation can be discontinued 15 to 25 days before harvest. Most common irrigation methods are furrow and baain.

YIELD AND QUALITY

Frequent irrigation is required to prevent cracking of the bulb and forming of ’ doubles*. Also adequate water supply is essential for a high quality crop. A good bulb yield under irrigation is 35 to ^3 ton/ha. The water utilization efficiency for harvested yield (Ey ) for bulbs containing 85 to 90 percent moisture is 8 to 10 kg/mJ.

PEA

Pea ( Pisum sativum) is grown as a vegetable crop for both fresh and dried seed. Present world production is about 13. 5 million tons dry pea and ^ .8 million, tons fresh pea.

The varieties range from tall climbing to small bunch types with the latter having a shorter f law ing period. Pea is a cool climate crop and optimum mean daily temperature is 17°C with a imnimum of lO^C and a maximum of 23°C. Germination is affected by soil temperature; at 5°C oerminaiion takes 30 days or more, at lO^C about 1 days and at 20 to 30®C about 6 days. Young plants can tolerate light frost but flowers and green pods are injured by light frost. In the tropics near the equator, peas are grown at .tout 1 500 m altitude, or as a winter crop in areas away from the equator. The normal growing period is 65 to 100 days for fresh pea with an additional 20 days for dry peas. The growing period is extended under cool conditions.

The crop does well on most soils with good drainage and pH of 5* 5 to 6 .5 . F e r t i l ize r requirements are about 20 to 1,0 kg/ha N , ^0 to f i ) kg/ha P and & to 160 kg/ha K . Pea is capable of fixing atmospheric nitrogen, which meets ita requirements for high yields. However, a starter dose of 20 to dO kg/ha N is beneficial for good early growth.

Pea IS sensitive to soil salinity with yield decrease at different levels of ECe similar to that of bean, or 0% at ECe 1.0, 10% at 1.5, 25% at 2.3 , 50% at 3 .6 , and 100% at ECe 6. 5 mmhos/cm.

Plant spacing depends on variety and type and whether bunch or climbing, and 11 between 0.6 to 0 .9 x 0.05 to 0. 1 m with a wider spacing when grown along with stakes. Depth of sowing is 2 to 5 cm. Prevention against root rot requires good drainage and rotation. Common rotation crops are alfa lfa , potatoes and sugarbeet.

W M F ? PFOIMRFMFNTS

Water requirements (ETm) of pea are similar to bean (350 to 500 mm). The crop coefficient (kc) relating maximum evapotranspiration (ETm) to reference evapo- tronsptration (E T o ) is : dunng the initial stage O.A (10 to 25 days), the development stage 0 .7 -0 .0 (25 to 30 days), the mid -season stage 1.05-1*2 (25 to 30 d ays ), the late- •eason stage 1 .0 -1, 15 <5 to 10 days) ( fresh ) and 0.65-0.75 (20 to 30 days) (dr ied ), and at harvest 0.95-1. 1 (fresh ) and 0.25*0.3 (dried ).


The growing periods of pea are :frggh dried

0 establishment 10-25 10-25 days1 vegetative 25-30 25-302 flowenng (inclu<hng pod set) 15-20 15-203 yield formation (pod development and

pod filling) 15-20 20-25

" s l e f e M i i . , .

M 3

The relationships between re la t iv e yield d ec rea se (1 - Ya/Ym) and re la t ive evapotranspiration de f ic i t ( I - ETa/ETm) are shown in F igure 24. For calculation examples see p* 40 and Chapter V I .

»-

frwft and dry pM p iid liDiai yowdn pwDd

-1---------- *------------L.

F ig . 24 Relationship between re la t ive yield d ec rease (1 - Ya/Ym) and re la t ive evapotranspiration defic it (1 - ETa/ETm) fo r

pea

The sensit ive per iods fo r water de f ic i ts are f lower ing (2 ) and yield formation (3 ) . Unlimited water supply during the vegetat ive per iod (1 ) increases vegetat ive growth but may not necessar i ly affect the pea y ie ld ; water defic it in this period has a r e la t i v e l y small ef fect on y i e ld . S im i la r ly , water defic it during the ripening period for dry peas has a small ef fect on y ie ld .

When rainfall is insufficient, i r r igat ion during the f lowering period (2) increases the number o f marketable pods and number o f seeds pe r pod, and during the yield formation period (3) increases the weight o f both pod and se<^. The crop tends to wilt more readily during periods o f water shortage when adequate water was a va i l able in the preceeding per ic^s .

For high y ie ld s the soil water depletion should not exceed 60 percent o f the total available soil water during the vegetat ive period (1), and 40 percent dunng f lowering (2 ) and yield formation (3) per iods . Too frequent and light irr igat ion appli* cation results in uneven ripening. With harvest consisting of one picking it is sometimes recommended to withhold w a t e r supply dunng the latter part of the yield formation per iod (3) to advance npening of the most developed pods. Th is applies part icular ly to vai 'iet ies with a long and non-uniform ripening p en od .

Under conditions o f limited water supply a high total production is obtained by meeting full crop water requirements on a limited area rather than by extending the area and partia l ly meeting crop w a te r requirements.

114

The crop has a tap roo i with many ihin la te ra ls . Rooting depth in deep so i ls can extend to 1 to 1 . 5 m but the e f fe c t iv e depth o f water uptake is genera l ly res tr ic ted to the f irs t 0 .6 to 1 .0m (D - 0 . 6 - 1 . 0 m ) . The uptake pattern o v e r soil depth, h o w e v e r , depends g r ea t ly on the i r r iga t ion p rac t ices . The uptake o f water in re lat ion to ETm is t ittle affected up to soil water depletion o f about ^0 percent o f total ava i lab le soil water (p • 0 .^ ) .

WATER UPTAKE

IRRIGATION SC H E D U L IN G

For optimum y ie ld leve ls the soil water dep le t ion in most climates should not exceed < 0 percent o f the total ava i lab le soil water and ir r iga t ion frequencies o f 7 to 10 days a rc common. When water supply is short, i r r iga t ion should be adequate during the f lower ing (2 ) and y ie ld formation (3) per iods with poss ib le savings during the vegetat ive (1 ) and ripening (^ ) pe r iods . When frequent i r r iga t ion is not poss ib le , water supply should be scheduled as p r e - i r r i g a t i o n , at f lower ing (2 ) and at the y i e ld formation period (3 ) r e sp ec t iv e ly , o r with one i r r iga t ion only at least about 4.0 to 60 dav*i a f t e r the r r r - 1 r r i cjarion ,

Y IE L D AND Q U A L IT Y

When ir r iga t ion is i r r e g u la r , pods and seeds a re less uniform in s ize , more var iab le in co lour and also the date o f maturity will va ry . A high water def ic i t during late y ie ld formation results in tough seeds o f poor quality. In genera l , increase in s e ^ s ize is accompanied by a decrease in the sugar content and the tenderness o f the seed, and an increase in the starch and protein contents. C o r rec t timing o f the harvest remains an essential requirement for a good quality p roduc t . In suitable cl imates, good y ie lds under ir r iga t ion are between 2 and 3 ton/ha shelled fresh pea ( 70 to 80 percent moisture) and 0 .6 and 0 .8 ton/ha dry pea (12 percent moisture). The water utilization e f f ic iency for harvested yield (E y ) for fresh pea is about 0 .5 to 0 .7 kg/ m and fo r fresh pea about 0. 15 to 0.20 kg/m^.

PEPPER

Pepper ( Capsicum annum and Capaicum f rutescens) » » thought to originate from tropical Am erica . Most o f the peppers grown belong to Q. annum but the small, pungent pepxpers belong to C- fru tescens. Pro'-cm world production is abov;t 5 million tons fresh fruit from 0 .7 million ha.

Pepper thrives in climates with growing season temperatures in the range o f 16 to 27®C during the day and 15 to 18*^C during the night. Lower night temperatures result in grea ter branching and more f low ers ; warmer night temperatures induce ea r l ie r now erm g and this effect is more pronounced as light intensity increases

The crop is grown extensively under rainfed conditions and high yie lds are obtained with rainfall o f 600 to 1 250 mm, well-d istributed over the growing season. Heavy rainfall during the flowering period causes flower shedding and poor fruit setting, and during the ripening period rotting of fruits.

L ight-textured soils with adequate water holding capacity and drainage are p re fe r red . Optimum pH is 5*5 to 7.0 and acid soils requ ire liming. W aterlogging, even for short per iods, causes lea f shedding, F opttI , ' o r r o n m « . i r e to 1 "^0kg/ha N , 25 to 50 kg/ha P and 50 to 100 kg/ha K .

The crop is moderately sensitive to soil salin ity, except in the seedV^ng iitage \K\icn it is more sensitive. Y ie ld decrease at different leve ls o f ECe is : 0% at ECe 1. 5 mmhos/cm, 10% at 2 .2 , 25% nt 3 .3 , 50% at 5. 1 and 100% at ECe 8 .5 mmhos/cm.

Seeds are sown in nursery beds which in the coo le r climates aro sometimes enclosed and heated since soil temperatures in the range of 20 to 2i®C are considered optimum for germination. Seedlings o f 10 to 20 cm height are transplanted in the field after 25 to 35 days. The length of the total growing penod va n es with cl imate and varie ty but in general it takes 120 to 150 days from sowing to the latest harvest.P r io r to transplanting, the seedlings raised in enclosed and heated nurseries are hardened by increased ventilation. The plants are sometimes lopped 10 days before transplanting to encourage branching. Plant spacing is 0 , C to O.o m x 0 .9 tn* For production o f fruits for canning, c loser spacings are sometimes used. F lowering starts 1 to 2 months a fter transplanting with first picking of green peppers 1 month la ter. Th erea fte r , r ip e , red peppers are picked at 1 to 2 week intervals for up to J months. Ripe ch ill ies arc semi-dried for 3 to 15 days, with the final weight being about 25 percent o f the fresh fruit weight.

W ATER REQLMREMENTS

Total water requirements (ETm ) are 6OO to 900 mm and up to 1250 nun for long growing periods and several pickings. The crop coeffic ient (kc ) relating re ference evapotranspiration (E T o ) to maximum evapotranspiration (ETm ) is 0 .^ following transplanting. K ' 1 .1 31;ring fiTI ^.^ver and f ^ 0.8 t o

0 .9 nt time o f harvest.

W ATER S U P P L Y AND CROP Y IELD

The relationship between re lative yield decrease and re la t ive evopoiranspir ation defic it is give\ \ * ’ . - gi • period ir ro ? ' .

116

F ig . 25

Relationship between re la t iv e y ie ld d e c rea se (1 - Ya/Ym) and r e la t iv e evapotranspirat ion de f ic i t (1 - ETa/ ETm) fo r pepper

For high y ie ld s , an adequate water supply and re la t iv e ly moist soi ls a re required during the total grow ing per iod . Reduction in water supply during the growing pen od in general has an adverse ef fect on y ie ld and the grea tes t reduction in yield occurs when there is a continuous water shortage until the time of f irs t p icking. The per iod at the beginning o f the f lower ing per iod is most sensit ive to water shortage and soil water depletion in the root zone during this per iod should not exceed 25 p e r cent. W ater shortage just p r io r and during ea r ly f low er ing reduces the number o f fruits . The ef fect o f water de f ic i t on >neld during this period is g r ea te r under con

dit ions o f high temperature and low humidity. Control led ir r iga t ion is essentia l fo r high y ields because the c r o p is sensit ive to both o v e r and under i r r iga t ion (F ig u r e 26).

So4 «V*«r dMMion

F ig . 26

Relationship between re la t iv e yie ld d ec rea se ( I - Ya/Ym) and soil water depletion fo r pepper

With poor quality (saline) water the yield of first pickings is reduced but the effect is less pronounced on later pickings. Sprinkling with poor quality (saline) water causes leaf bum and 'nose ro t ’ of the fruits. Water deficits during yield formation period lead to shrivelled and malformed fruits. The pungent qualitv of the fruit (hotness) con to a certain degree be influenced by water supply.

Under conditions of limited w a te r supply, total production is increased by meeting full crop water requirements over a limited area, rather than by extending the area and partially meeting the crop water requirements.

117

W ATER U PTAKE

Pepper has a tap root which is broken at the time of transplanting and a profusely branched lateral root system subsequently develops. Root depth can extend up to 1 m but under irrigation roots are concentrate mainly in the upper 0.3 m soil depth. Normally 100 percent of the water uptake occurs in the first 0 .5 to 1.0 m soil depth CD - 0. 5- 1*0 m). Under conditions when maximum evapotranspiration is 5 to 6 mm/day, 25 to 30 percent of the total available soil water can be depleted unt il soil water uptake w i l l be reduced (p - 0.25 to 0.30).


For optimum yield levels the soil water depletion in most climates should not exceed 30 to LO percent of the total available soil water. Due to the low depletion level light irrigation applications are required. Irrigation frequencies o f ^ to 7 days are common. When water supply is short, irrigation should preferably be adequate up to the first picking and savings may be made thereafter.

IRRIGATION METHODS

Peppers are grown under surface, sprinkler and drip irrigation. With sprinkler irr igation, yields tend to be higher under light applications as compared to heavy intensity sprinkling. However, with poor quality water, heavy intensity and large amounts are generally preferred with sprinkler irrigation because of reduced le a f burning and improved leaching of salts. The crop is particularly suitable for drip irrigation \ nrv hi.;h v oMs can be obtained.

YIELD AND Q U ALITY

Yields vary greatly with climate and length of growing period , e .g . number of pickings. Under irrigation commercial yields are in the range of 10 to 15 ton/ha fresh fruit and 20 to 25 ton/ha are obtained under favourable climatic conditions. However, the marketable yield percentage may vary. Number of pickings is I for machine harvesting and up to 6 for hand picking, depending on the length of the harvesting period. The water utilization efficiency for harvested yield (Ey ) for frr^h pepper containing about 90 percent moisture van es between 1.5 and 3.0 kg/n

PINEAPPLE

Pineapple (Ananas comosus) is a perennial crop grown fo r its fruits and used as a fresh and processed product. World production is about 5 .5 n ii lh on tons fresh fruit.

The orig in of the pineapple is still uncertain but the Parana-Paraguay Basin has been considered as a possib le a rea . For good growth pineapple requ ires mean daily temperatures o f 22 to 26®C with an optimum o f 23 to 24^C. Mean da ily aiaximurn and minimum temperatures o f 30 and 20^C respect ive ly for the whole g row in g penod are considered optimum. Temperatures below o r above this range affect fruit quality o r the acid and sugar content.

The crop is grown between 3 1 ^ and 34*^5, prim arily m regions with high re la t ive humidity* A combination of optimum temperature and high humidity results in soft, targe leaves and juicy fru its , low in acid content. Fru its ripening in periods with cool temperatures and low radiation le v e ls , e .g . in w inter o r at high altitudes, are o f in fe r io r quality because o f poor shape for canning. Requirements fo r canning are : a cy lindrica l shape, fruit eyes o f a re la t ive ly shallow surface and a small fruit core in relation to the fruit.

Pineapple can grow on a wide range o f so ils but a sandy loam texture is p r e fe r r e d . Optimum soil pH is 4, 3 to 6. 3* The soil should have a low lime content.The crop IS sensitive to w a te r logg in g and there fore requ ires a well-dra ined soil with good aeration. For high production the f e r t i l i z e r needs arc 230 to 300 kg^ha N , 4 j to 65 kg/ha P and 110 to 220 kg/ha K .

Pineapple is usually grown m double rows on ra ised beds. With a spacing of 0 .6 X 0-3 m in beds 0 .75 to O.90 m apart, plant population is about 50000 p er ha. Shading IS sometimes used where temperatures arc high and radiation intense to p ro tec t the crop from scorching. The crop is multiplied using s lips , crowns and shoots o r suckers, but in comparison with using suckers as planting material, the period from planting to harvest is about 20 percent longer when slips are used, and about 35 percent longer when crowns are used. Use of different planting material a l low s a mampulation of the crop growing pen od and particu larly in selection o f the time o f harvest when

cUmatic conditions a re favourable fo r high quality fruits. Normally the plant crop is followed by one ratoon crop , but when climatic conditions a re favou rab le , the crop will continue to bear fruits but quality rapidly declines a fter the first ratoon. H ow ever , in warm tropical c lim ates, e . g . at low altitudes near the equator, no ratoon crop is possib le because suckers do not develop. The p e r iod from planting to harvest o f the plant crop is 1 to 2 years and o f the ratoon crop 9 months to 1.5 years depending on planting mater ia l and climate.

F low er initiation in p ineapple IS induced by low tempcra-

Crow

wrop, iirst ratoon and second ratoon (CoUins, I960)

119

ture, water deficit o r hormone sprays; the U tter results in a uniform fruiting and harvest per iod .

WATER REQUIREMENTS

Crop water requirements (ETm) fo r high production are very different from those of most other crops. Because there is a suspension of transpiration during the day, maximum evapotranspiration is low and van es between 700 end 1000 mm per year The crop coefficient (kc) relating reference evapotranspiration (E T o ) to ETm is about0.4 to 0. 5 for the total crowing period .

V«g«1at<v* (1 I FtOMwanng i j ) (3l ar«i n.p«n>r.g HI

>3 nwntPka 3-1 mortiha 3-S moMiHa

Fig. 2S Growth periods of a 20-monih pineapple(a fter E .A .C . , 1977)

\;^ATER S U P P LY AND CROP YIELD

a NT *npineapple can survive long dr> perious u.rougti ii> i. reta^\ »dN'the leaves which is used during these penods. Also due to its low water use, the plant can survive on a small depth of stored soil water. However, the crop is sensitive to water defic it, especially during the vegetative growth period, when the size oxtd fruiting characteristics are determined. Water deficits retard growth, flowering and fruiting. Water supply during this period should meet full water requirements o f the crop. Water deficit at flowering has a less serious effect and may even hasten fruiting

end result in uniform npening. An ample water supply at flowering wiU lead to vigorous stem growth and a large core which is disadvantageous when the fruit is used for canning.

Frequent irrigation or ram at the time of harvest may cause deterioration of the quality of the fruit and make the crop susceptible to the fungus causing heart rot. In addition, waterlogging affects fruit quality.

Where water supply is limited, mulching is practised to reduce soil evaporation and soil temperature. Dew has been found to contribute to meeting the waier requirements o f the crop.

120

WATER U PTAKE

The rooting system o f pineapple is shallow and sparse. In deep soils, maximum root depth may extend up to 1 m but roots are generally concentrated in the first 0 .3 to 0 .6 m, from which normally 100 percent of the water is extracted G) • 0.3 0 .6 m).* Under conditions when maximum evapotranspiration is 5 to 6 mm/day, water uptake starts to be reduced when about 50 percent o f the available soil water has been depleted (p - O . j ) .


Adequate water supply is essential particularly during the vegetative period. The interval of application can be based on the prevailing rate of maximum evapotranspiration (ETm) and the fraction (p) o f the total available soil water. Where rainfall is small and irrigation water supply is restr icted , irrigation scheduling should be based on avoiding water deficits dunng the period of vegetative growth (1). Supply of water can be res incted dunng the penod of npening (4) whereas some water savings can be made by allowing higher depletion levels up to 75 percent during flowering (2), During the month p r io r to harvest irr igation is discontinued. The method of i rn g a i io n is mostly by apnnk ler.

Y IELD AND Q U ALITY

The fruit contains about 80 to 85 percent water and 10 to 14 percent sugar. Irrigation has an effect on the sugar/acid ratio, particularly in the period p r io r to harvest when frequent high irrigation decreases the sugar content. The infestation by so il-bom e fungus diseases is increased.

Under commercial production, weight per fruit is about 1-5 to 1,8 kg, and total yield between 75 and 90 ton/ha fresh fruit. The water utilization efficiency for harvested yield (Ey ) for fresh fruit is about 5 to 10 kg/m^ for the plant crop and 8 to 12 kg/ai* for the first ratoon crop.

POTATO

Potato ( Solanum tuberosum) originates in the Andes from the tropical areas of high altitude. The crop is grown throughout the world but is of particular importance in the temperate climates. Present world production 19 aome 290 million tons fresh tubers from 21 million ha-

Yields are affected by temperature and optimum mean daily tetnpcraturea are 18 to 20®C. In general a night temperature of oelow 15®C is required for tuber initiation. Optimum soil temperature for normal tuber growth ta 15 to 18®C. Tuber growth IS sharply inhibited when below lO^C and above 30®C. Potato varieties can be grouped into early (90 to 120 days), medium (120 to I 50 days) and late vaneliea ( I 5S to 180 days). Cool conditions at planting lead to slow emergence which may extend the growing period. Early varieties bred for temperate climates require a daylength of 15 to 17 hours, while the late varieties produce good yields under both long or short day conditions. For tropical climates, varieties which tolerate short days are required for local adaptation.

Potato IS grown in a 3 or more year rotation with other crops such as maize, beans and alfalfa, to maintain soil productivity, to check weeds and to reduce crop loss from insect damage and diseases, particularly soil-bome disease. Potato requires a well-drained, well-aerated, porous soil with pH of 5 to 6. Fertilizer requirements are relatively high and for an irrigated crop they are 80 to 120 kg/ha N, 50 to 80 kg/ha P and 125 to I60 kg/ha K. The crop is grown on ridges or on flat soil. For rainfed production in dry conditions, flat planting tends to give higher y ie lds due to soil water conservation. Under irrigation the crop is mainly grown on ridges. The sowing depth is generally 5 to 10 cm, while plant spacing is 0.75 x 0.3 m under i r r ig ation and 1 X 0.5 m under rainfed conditions. Cultivation during the growing period must avoid damage to roots and tubers, and in temperate climates ridges are earthed up to avoid greening of tubers.

The crop is moderately sensitive to soil salinity with yield decrease at different levels of ECe: 0% at 1.7, 10% at 2.5, 23% at 3.6, 50% at 5*9 and 100% at ECe 10 mmhos/cm.

WATER REQUIREMENTS

For high yields, the crop water requirements (ETm) for a 120 to 150 day crop are 500 to 700 mm, depending on climate. The relationship between maximum evapotranspiration (ETm) and reference evapotranspiration (ETo) is given by the crop coefficient (kc) which 1 s : during the initial stage 0.4-0. 5 (20 to 30 days), the development stage 0.7-0.8 (30 to 40 days), the mid-season stage 1,05-1.2 (30 to 60 days), the late-season stage 0.85-0.95 (20 to 35 days), and at maturity 0.7-0*75.


The growth periods of potato are given in Figure 29. The rcUnonship between relative jaeld decrease and relative evapotranspiration deficit la given la Figure 30. For calculation examples sec p. 40 and Chapter VI.

\ 22

%

IS-M •M Swit 0»*Wf«Wit* ▼wS«*« at M « a t r.nal

wa.f**Vinaa an« M io ea c *catawr,no ll'

iSf

iS*t» «av«

v*e«taita«n> t ta i a t iki

m~m « - »—r*

lo-ti ••r«

t «.aa«ty —tpinT*•* **«*«»•* t<«.t.ai.«o

Eig. ^9 G row th p e r io d s o f po ta toes (a f t e r W .C . S p a rk s , 1972)

Potato IS re la t iv e ly sensit ive to soil water de f ic i ts . To optimize y ie lds the total avai lable soil water should not be depleted by more than 30 to percent. Depletion of the total avai lable soil water during the grow ing per iod o f more than 50 percent results in low er y ie ld s . Water de f ic i t during the per iod o f stolonization ar^ niber initiation ( l b ) and yield formation (3 ) have the greatest adverse e f fect on r i c ld , whereas npening (^ ) and the ea r ly vegetat ive ( l a ) per iods a re less sensit ive .In genera l , water de f ic i ts in the middle to late part o f the growing per iod thus tend to reduce yield more than in the ea r ly part. H ow ever , va r ie t ie s vary in the ir sensit iv ity to water de f ic i t . Some v a r i e t i e s respond better to ir r iga t ion m the e a r l i e r part o f the yield formation per iod (3 ) while others show a better response in the l a t t e r part of that per iod . Y i e ld s o f va r ie t ie s with few tubers may be somewhat less sensit ive to wster de fic it than those with many tubers.

To maximize y ie ld , the soil should be maintained at a r e la t iv e ly high ssoisture content. Th is , however , can have an adverse e f fect when frequent ir r iga t ion with re la t ive ly cold water may d ec rea se the soil temperature below the optimum value o f IS to 10^C fo r tuber formation. A l s o , soil aeration problems can sometimes occurir wrT . s o tN ,

123

Since (he potato is a re lative ly senstttve crop m terms of both yield and quality, under conditions of limited water supply the ava ilab le supply should preferably be directed towards maximizing yield per ha rather than spreading the limited water over a larger area. Savings in water can be made mainly through improved timing and depth o f irrigation application.

WATER U PTAKE

Under evaporative conditions with ETm of 5 to 6 nan, the effect o f soil waterdepletion up to 25 percent on yield is small (p - 0 .25). Since potato has a shallow root system, normally 70 percent of the total water uptake occurs from the upper 0 .3 ■ and 100 percent from the upper 0.^ to 0.6 m soil depth (D - 0 .^ -0 .6 m). The uptake pattern w ill , however, also depend on the soil texture and structure.


Where rainfall is small and irrigation water supply is restricted, irngstion scheduling shcula be based on avoiding water deficit during the period of siotonizaiion and tuber initiation ( lb ) and yield formation (3). Supply of water can be restricted during the early vegetative ( la ) and ripening (L) periods. Savings can also be attainad by allowing higher soil water depletion toward the ripening period (L) so that all ava ilable stored water in the root zone is used by the crop. This practice may also hasten maturity. Correct timing of irrigation may save 1 to 3 irrigation applications including The last i rr igat ion p r i o r to harvest.

l O O S o s a r o s o s o s Q s o t O i o l O O S O S O r o s O t O i O J Ol 01 0.|0

ot

m m Oi

/ / im 05 V

. / M04

C5

OS

or

o«

fmm fWW os

>0

01

OS

o*

or

Ftg. 30 Relationship betvaan ralanva yield dacraasa (1 - Ya/Ym) ralanva aaapotranspiratioo (1 - ETa/ETm) for potato

IRRIGATION METHODS

Most common irrigation methods for potato are furrow and sprinkler. Yield response to frequent irrigation is considerable because the crop has a shallow root system and requires a low soil water depletion. For example, very high yields are obtained with the mechanized sprinkler systems where evapotranspiration losses are replenished each o r every two days.

i : 4

YIELD AND Q U ALITY

Water supply and scheduling are important in terms of quality. Water deficit in the early part of the yield formation period (3) increases the occurrence o f spindled tubers, which is more noticeable in cylindrical than in round tubered varieties. Water deficit during this period followed by irrigation may resu lt in tuber cracking or tubers with black hearts. Dry matter content may increase s lightly with limited water supply during the npening period (4). Frequent irrigation does reduce occurrence of tuber malformation.

Good yields under irrigation of a crop of about 120 days in the temperate and subtropical climates are 25 to 35 ton/ha fresh tubers and in tropical climates yields are 15 to 25 ton/ha. The water utilization efficiency for harvested yield (Ey ) for tubers containing 70 to 75 percent moisture is 4 to 7 kg/m*.

RICE(paddy)

Rice (Qrv^a aativa) tt believed to originate from eeutheeat A»ta> The present world production is about 3 65 million tons from about 1^2 million ba>

In general, Indica rice is grown in the humid tropics and Japontca n ee is best suited lo temperate and subtropical climates. The total growing penod normally varies between 90 and 150 days depending on variety, temperature and sensitivtty to daylcngth. The early matunng vaneties arc day-neutral and the late maiunng vanetlcs are shon-day plants. The response of n ee to temperature differs with variety. In general, below 12^C germination does not occur. Rice seedlings from the nursery bed can be transplanted to the field when the mean doily temperature is about 13 to 15*^C. Temperatures between 22 and 30*^C are required for good growth at all stages but dunng flowering and y e ld formation small differences between dey and night temperatures are required for good yield. Optimum daytime air and water temperatures for the growth of rice are in the range of 28 to JS®C, The decrease of temperature of water during the night under hot conditions helps to maintain favourable water temperatures during daytime but should not decrease below 18^C.

Rice IS normally transplanted at random with an optimum spacing varying between 0.15 x 0. IS end 0.30 x 0.30 m.

A wide range of soils are suitable for rice cultivation but heavier soils are preferred due to low percolation losses . The crop has a h i^ tolerance to acidity srtth optimum pH between 5*5 and 6. For high production, fert il izer requirements are 100 to 150 kg/ha N , 20 to ^0 kg/ha P and 80 to 120 kg/ha K . Split applications before transplanting, at tillering and heading Have the greatest effect on yield. Nitrogen fertilizer application may be lower where there is a considerable biological N-hxation by blue- green algae and bacteria.

Rice is moderately tolerant to salinity. Y ie ld decreases for different salinity levels are: 0% at ECe 3.0 mmhos/cm, 10% at 3.8 , 23% at 5* 1 • 50% at 7.2 and 1(X>% at ECe 11.5 mmhos/cm.

WATFR RFO l’ lREM ENTS

iratton are betweenWater requirements ol paddy rice for evapotranspiration at 700 mm, depending on climate and length of the total growing period. Eveporotlot. losses tend to become somewhat smaller at shallow submersion or when the topsoil partially dries out. Evapotrsmspiration increases with vegetative growth and is highest Just before flowering to early yield formation, after which it declines somewhat. For paddy rtce, the maKtmum evapotranspiration (ETm) in relation to reference evapotrens- ptratton (ETo) is given by the crop coefficient (kc) for the different months or during the first month and the iiecond month 1.1 to 1.15. mid-sea son 1 .1 to I . J and the last month 0«9S to 1.05-


The growth periods o f rice are shown in Figure 31 and the relationship between relative jrteld decreese ( I - Ye/YsO and relative evapotranspiration deficit ( I - ETa/ETm) for the total growing period ere shown in Figure 32.

126

THANSrtANTINQ

P t m -T iR r - ' 1 ■

G r a in ^ t f l i n s < f n * p d n i n f

i S t V * 9 « i » t * V * 11 }v > d l«

f o r m a t i o n19}

H i p a n m s ( 4 >

11

4 0 - t o * d a y * to - 1* d * r a 20- 3 t d a y a 1 0 -1 0 d a y a

F ig . 31 Growth per iods o f r i c e

F ig . 32

Relationship between re la t ive y i e l d (1 - Ya/Ym) and r e la t i v e evapotranspiration (1 - ETa/ETm ) fo r r i c e

127

i// ///. , // V/" yy//*//:

0*v« O 90 J--------L J ! t

Fig. 33 Controlled water depth in paddy field (Kung, 1971)

Adequate water dunng the total growing penod is i^eded for vigorous growth and high yield. Because plants have to recover from transplanting and for formation of the roots, adequate water supply just following transplanting is important. For high yields, the water depth in the paddy field required at different growth stages is shown in Figure 33.

Cmmi (X ^oo

The most sensitive penods to water deficit are flowenng (2) and the second half of the vega* tative penod (head developinent). When moisttir# content of the soil deCroaaat to 70 to 80 percent of the saturation value, rtce yields begin to decline. At a soil water content of 50 percoat of saturation, yield decrease la 50 to 70 pare eat.At a aoil water content of 30porcaat, ao yteld can be expected and plants die when aotl water content is below 20 percent (Figure 34).

hig. 34 Relatiooship between relative yield decrease (1 - Ya/Ym) and auMsture content of the soil for rice

The root system o f r ice in c reases gradually from transplanting, reaching a maximum at the time o f heading, and d e c rea se s a f te r f lower ing while at maturity most o f the roots a re dead. Root growth continues under low oxygen concentrations in the so i l . At the lime o f head initiation, root growth is hor izontal and upward, producing a dense surface mat. Maximum rooting depth is about 1 m in the absence o f a dense subsoil la ye r

128

WATER UPTAKE

IRR IGATION SCHEDU LING

Severa l i r r iga t ion scheduling p rac t ic e s have been deve loped. Because paddy r i c e la mostly grown under condiiions o f near soil saturation and submersion, loss through perco lanon should be minimalt A dense subsoil laye r is obtained by puddling the wet soil which requ ires 100 to 200 mm of w ater , and sometimes up to 300 mm, including the p re - planting ir r igat ion*

- 'Continuous submergence’ with intermittent drainage is the most promising method (F igu re 33). During and immediately a fter transplanting the water is kept at 10 cm fo r about a week a f te r transplanting to secure healthy growth o f the seed l ings. In the fo l lowing t iU en n g pe r iod , submergence is shallow (maximum 3 cm) to maintain high soil temperatures. Drainage and dry ing o f the lop soil is pract ised during this per iod since n e e can to lerate a water shortage and root development is enhanced. Drainage must be completed 30 days p r io r lo heading. From this lime onward , adequate water supply during head development through f lower ing is essentia l . Because root act iv i ty at this time is at Its maximum, water temperature should pre fe rab ly be high but below 35®C. Continuous flow ir r iga t ion or dra inage and renewal o f w a t e r once o r twice during this per iod is sometimes pract ised . During the ripening per iod f ie lds should gradually be drained to faci l i tate harvest operat ions. Usually f ie lds are completely drained 30 to 45 days a fter heading, with the shorter period for ear ly r i c e va r ie t i e s and the longer for late v a r ie t i e s . Untimely drainage adverse ly a ffects y ie ld s .

-W ith the ’ intermittent ir r iga t ion method’ , soil water during the non-submersion per iod must be adequate. When the soil water content fa l ls slightly below saturation, water is added until a shallow submergence is attained. Intermittent ir r iga t ion saves water by reducing surface runoff and perco lat ion lo sses , and also increases the amount o f rainfa ll that is used e f fe c t iv e ly .

-With the 'heading stage submergence method', the soil is kept at saturation o r is lightly submerged during almost the whole grow ing per iod , except for a period o f 25 days p r io r to about 10 days a fter heading when n e e f ie lds are submerged to a depth o f 10 cm.

-When Water saving* is essent ia l , the field a fter puddling and transplanting is supplied with water to keep soil water content in the root depth at not less than 75 percent o f full saturation throughout the total growing per iod . Moderate submergence is only pract ised during a period of 30 days starting at head initiation t i ll the ^nd o f Dowering. Especia l ly on soils with high perco lat ion ra te s , substantial water savings up to 50 percent can be m ^ e .

to vontinuoui ibrnor«iion, water savings a re estimated:

water aoDhed Yield

continuous submersion 100% 100%intermittent irr igation heading stage submersion

80% 50%60% 75%

water saving irr igat ion ( c o n t r o l ! ^ ) 75% 110%

129

Although rivc IS an aquAtiv pLaui atui g ro ^ » well under tubmergctt conditions, deep and prolonged submersion of paddy nee adversely affects plant growth. High yielding vaneties are more susceptible to Hood damage than most traditional vaneties The most susceptible stages for whole plant submergence are head development and flowering. Relatively little damage is done when the head and upper leaves remain above the flood water surface (Figure 3S).

t-

Ona e mm 0«rtFig. 35 Relationship between relative yield decrease (1 - Ya/Ym) and

number of days of total submergence with clear and muddv waterfor n e e

Wa> s to decrease surface runoff and percolation include controlled submersion with high water depths practised only during a few selected stages of growth. Also, accurate land levelling and good puddling and impervious levees wi)l reduce water losses. To reduce excessive percolation on soil compaction or application of heavy soil ts practised. Artificial sealings, like polyethylene membranes, asphalt barriers or coiu rcTi' I'Drr’ cr* hii'. o Tru’ T oxncntit'nt,i 11 .

IRRIGATION METHODS

Basin irrigation is used for nee production. Fields should be level and both water supply and drainage should be fully controllable. Sue of the fields . an vary greatly depending on topography, land ownership and level oi water supplv

YIELD AND QUALITY

Alternate wetting and drying dunng the yield formation and npening penods may cause grain to crack. The crop should be harvested before the grain is completely dry since cracks arc more readily formed when the grain is quite h a ^ . Slow drying gives a higher percentage of whole grams while the ssoisture content of 20 percent is

130

someTimes used as a guide lo determine n peness o f the gram in the fie ld . A moisture content of 15 p rcent is c r it ica l fo r crack formation, while internal cracks occur at g rea te r dryness o f the seed.

Good y ie lds under fully controlled irrvgawon with high inputs are O to 8 ton/ha paddy (unm iU ^ r ic e ) . Under controlled flood irr igation good y ie lds are 3 to ^ ton/ ha. The water utilization e ff ic iency fo r harvested yie ld (E y ) fo r paddy containing about 15 to 20 percent o f moisture, is 0 .7 to 1.1 kg/m^. M il l in g percentage o f r ic e is about 65 percent.

FISH PRODUCTION

Rice and fish production can take place at the same time. The fish is e ither stocked (bred species ; o r is introduced with the irr iga tion water into the r ic e field (wild spec ies ). Standing water in the fields should be 5 to 25 cm, depending on fish s ize . Dunng periods of field drainage the fish should be able to take re fuge in supply and drainage ditches o r in specia lly constructed depress ions. Fish production in cropped paddy fie lds can amount to ^00 kg/ha/year. H ow ever, under conditions o f high crop and water management fo r r ic e production, the value of fish y ie ld genera lly does not balance the reduction in r ic e y ie ld . Problems are also experienced with use o f herb ic ides and pestic ides being toxic to fish.

R ice and fish production can be alternated when field layout and water contro l structures a re adapted to suit both n e e and fish production. High r ic e y ie lds and high f ish production can be obtained. For fish production the fields should be adequately fe r t i l iz ed , and additional feeding is normally required. With a proper combination o f fish spec ies , good production is 5 to 10 lon/ha/year. Species commonly used in combination with r ic e cultivation are common carp (Cvprimus ca rp io ), T ilap ia spp. sepat Siam (T n c h o g a s te r p ec to ra l is ) and kissing guromi CHelostoma temmmcki).

Sea also H. Tsuisui, W ater management m paddy fields. FAO Irrigation and Drainage Paper. In press.

SAFFLOWER

Safflow cr ( C dn h m u s t in c lo n m ) is only known m >t» cu lt iv «i«d form wiih cen tre* o f orig in probably in the Near EAsi. The estimated world production is about 0 .7 million tons o f seed per year from about 1 million ha* The flow ers from the spiny cu ltivars are grown fo r o i l , while some spineless cu tlivars are used for dye production.

Safflow cr IS fiot si.iit'ii u k'wiai.ii, tropics. Large scale commercialcropping IS practised in USA and USSR between 30^ and ^ 5 ^ and in Australia between 13^ and JS*^S. bmcrging plants need cool temperatures for root growth and rosette development (mean da ily temperature 15 to 2(K>C) and higher temperatures during stem growth, flow enne and yield formation periods (20 to 30^C). There is no germination below 2^C. At s 'c germination takes 16 days and at 16^C, A days* The seedling is fro s t-res t slant up to -T^C but a fter this stage frost below -2®C kiUs tha plant* The crop seems to be sensitive todaylength but the effect is difhcult to quantify. The length o f the grow ing period for an autumn-planted crop van es from 200 to 2J0 d.iv..: when planted in sprtng, 120 to 160 days*

Safflow er requ ires a fe r t i le , fa ir ly deep an.: -^ ..d ra in ed soil. ; i : : ,;aied production a medium-textured soil is p referab le* Shallow soils seldom produce high y ie ld s. On suitable so ils roots go down lo 3*5^1; dense subsoils retard root growth. The crop is w ell adapted to the presence o f a water taMe at a depth o f up to 1 m.Under ir r ig a t io n , the fe r t iliz e r requirement* are 60 to 110 kg/ha N , 1S to 30 kg/he P and 25 to AO kg/ha K* Though there is a rather wide tolerance to pH , h l ^ yte loe a re obtained on soils with a neutral reaction ; when pH is tower than 6 liming may be advisable.

The crop is moderately tolerant to salin ity, ranking just below cotton. Y ie ld decrease due to soil salinity is :

at ECe 5 .3 , lOV at 6 .2 , 23^ at 7 .6 , 5 » at 9-9 and KXA at ECe 1A.5 mmhos^cm. Dunng germmation the seedlings ere about half a* to lerant, which is re la tive ly igh compared to other crops.

Row spacing van es from 0. 5 to 0 .8 m, wiO 35 plants per metre of row . Saad rate fo r broad. > sowing o f the irriga ted crop is AO to 50 kg/hai for row crops , sri'^ r I t ; V TC ? . if c 'ha.

F ig . 36 AalJtower, spiny c u .io s r during flow ering penod (Wei*'

The reputation of aafnowcr a* a drought resistant crop I * m a in ly based on its ability to withdraw water f a depth o f up to 3*5 m. It has prorad , how ever, to have well-defined water requiramente. For optimum crop y ta U a , the total water retfutrement* vary b«twe«n 600 and 1 200 aua depending on climate and length o f total growtag panod . Tba crop v a ta r raquireaianis ( I T o i ) aa reUtad to rafaranca avapoiransptraiton aaa gjvan by dia pop coafficiants (k c ): tmtial stage 0 .3 *0 .d 0 0 ta 35

days)t crop developownt stage 0 . OS M 7S days) mid-aaason stage stage 0 .65 -0 .7 (25 to AOmtd-aaason siege 1.05-1*2 (AS to 65dgjra)i loia season

days) and at banrast 0 .21-0 .25*

I

Safflow er is particu lar ly susceptible to excess water because o f its reaction to d iseases under wet conditions. Excess ive humidity, espec ia lly fog, induces head ro tj excess ive soil water causes root ro t : excess ive ram at f low en n g (period 2) adverse ly affects pollination and prevents complete seed f il l ing which may not be noticeable in the fie ld ; excess ive ra in fa ll a fter the crop reaches maturity leads to seed germination in the head.

The relationships between re la tive yield reduction and re la t ive evapotranspiration defic it based on interpreted information are shown in F igure 37. Water defic its dunng the ea r ly vegetative penod ( l a ) and the late vegetative period ( l b ) cause a reduction in growth and prolong the total growing period . Sa ff low er to lerates p en od s o f water defic it but fo r maximum production flowering and yield formation (3) are the most sensitive periods to water de fic it. Under conditions o f limned water supply, overa ll production is increased by extending the area and partia lly meeting (he crop water requirements rather than by meeting the full crop water requirements o ve r a limited area.

WATER s u p p l y AND CROP YIELD

HiETq f Tm

R elation ships between re laii % o > lol.i aoc reaso ( i - ) u, ;u) auu re lative evapotranspiration defic it (1 - ETa/ETm) fo r safflower

For a I55*day total growing penod the length of the different growth periods

0 cstabli shmentla early vegetative (rosette development) lb late vegetative (elongation and branching) 2 flowenng

*eld formation (seed filling) r ipening

4-10 days2560JO2510

2 5 0 - l5o days

I Vi

7 he rooting system oi safflower is extensive and m deep soils mayextend to 3 . 5 m, but normally 100 percent o f the water uptake of a full g ro w n crop takes place from the first I to 2 m vD * KO-2.0 m). Under conditions when maximum evapotransptrotion is 5 to 6 mm/day, water uptake starts to be reduced when 60 p e rcent of the total available soil water has been depleted.



Irrigation scheduling should be aimed at minimizing excess sotl water, particularly m relation to the sensitivity of the crop to root rot. A deep pre-planting irrigation is therefore very effective, followed by infrequent but heavy applications of water. Due to the deep rooting already during the early vegetative pencil (1 a ), thesoil depth miist he considered when deciding on the desirability of heavy watering*

In d e ep s o i l s with high water holding capacity, usually two irrigation applications are sufficient, i .e . one before planting and one dunng nowenng. However, a frequent mistake is a too early second application. On sous of lighter texture or when evapotranspiration demands are high, three or more applications may be necessary.

IRRIGATION METHODS

The crop is most commonly grown under surface irrigation, by the border method, allowing heavy irrigation applications. Also subirrigauen is used and gives high yields.

Y I L L U AN.^ Q L ’ A L l i i

Under ramfed conditions yields depend on initial toil water storage and on the rainfall durmg the growing season. Good ramfed yields are in the range of I to 2.5 ton^ha; under irrigation m the range of 2 to ton/ha. The water otiUxatlon efficiency for harvested yi.'’ ' r a , '".'i xfir.' v*r - r* 2and 0.5 kg/m*.

The oil content vanes from 20 to ^ percent depending on the vanety and some recently developed Indian vaneties may yield up to SO percent oti. These new vanetie* are early maturing, more cold resistant and spineless, but are more susceptible to root rot and rust.

SORGHUM

Sorghum (Sorgluim bi c o lo r ) appears to have been domesticated in Ethiopia about 5000 y ea rs ago. P resen t wor ld production is about 52 mill ion tons grain from LL mill ion ha.

Sorghum has a number of features which make it a drought-res is tant crop .It IS ex tens ive ly grown under rainfed conditions for grain and forage production.In dry areas with low and/or e r ra t ic rainfall the crop can respond v e r y fax'ourablv to supplemental i r r iga t ion . H ow eve r , considerable d i f f e ren ces exist amongst va r ie t ie s in their response to ir r iga t ion and those that a re considered v e ry drought- re t is tan t respond slightly while others produce high y ie lds under i r r iga t ion but arc poor y ie ld ing when water is limiting. Temperature is an important factor in var ie ty se lect ion . Optimum temperatures for high producing va r ie t i e s are o v e r 25®C but some va r ie t ies are adapted to low er temperatures and produce accep tab le v ie lds .When mean daily temperatures during the grow ing season are g r ea te r than 20®C , ea r ly grain va r ie t i e s take 90 to 110 days and medium va r ie t ie s 110 to 1^0 days to mature. When mean daily temperatures a re be low 20 °C , there is an extension of about 10 to 20 days in the growing per iod for each 0, 5°C d ec rea se in temperature, depending on v a r ie t y , and at 15°C a sorghum gram crop would take 250 to 300 days to mature. With mean daily temperatures m the range o f 10 to 15®C, the sorghum crop can only be grown as a forage crop because o f the problems w ith seed set and gram maturity under cool condit ions. Low temperatures ( < 15°C) during f lower ing and y ie ld formation, and high temperatures ( > 3 5 ° C ) lead to poor seed set, problems with r ipening and r ^ u c e d y ie lds .

For optimum light interception the density index (plants p e r ha « row spacing) IS about 3 (XX) when adequate water and fe r t i l i z e r s are ava i lab le (UX) (XX) to IjOCXX) plants pe r h a ) . In areas where water (ra in fa l l + i r r iga t ion ) is m short supply, the g rea te r the shortage, the g rea te r is the advantacc *■ ' lor spacing. Sorghum is ash on -day plant but day-neutral va r ie t ie s ex ist .

The crop does well on most so i ls but better so in light to medium textured soils The soil should p re fe rab ly be w e l l - a e ra t e d and we 11-d ra ined . Sorghum is r e la t ive ly to larant to short per iods o f water logg ing . The f e r t i l i z e r requirements a re up to iSO kg/ha N , 20 to ^5 kg^ha P and 35 to So kg/ha K .

Sorghum is moderately tolerant to soil salinity. Y ie ld d ec rea se due to so il salinity under irr igat ion i s : 0% at ECe .i mmhos/cm, 10% at 5*1* 25% at 7*2, jO% at U and 100% at ECe 18 mmhos/cm.

W A T E R R E Q U IR E M E N TS

• o r high production crop water requirements (E T m ) of 110 to 130 day sorghum batween <50 and 650 mm depending on the c Itmate; to this the losses during con-

application must be added. The crop coef f ic ien t (k c ) re la t ing maximum avepotrenspiration (ETm) to re fe rence evapotranspiration (E T o ) i s : during the initial stage ( f c VO 25 the development stage 0. 7-0. 75 (30 to <0 days ) , the mid-season ataae to <5davs). the late season stage 0.75-0-6 (30 days) and atharvest 0.5-0.55*

w

W A T T ? ST»PP1 y A V n r p O P YIELD

ihe growth pcncHla ol sorghum are:

0 cstsbUshment, from sowing to head inmaiton1 vegetative, from head initiation to head emergence2 flowering, from emergence to seed set3 yie ld formstion, from seed set to physiological mstuntv d ripening, from physiological matunty to harvest

15*20 2 0 - 3 0

I S - 2 0

3 5 - ^ 0

m

days

5 days

The relationships between relative yield decrease ( I - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ETm) are shown m Figure 38* For calculation examples see p. iO and Chapter VI.

i ig. 38 Relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ETm) for sorghum

Sorghum is relatively more drought-resistant than many other crops, e .g . maize. This is due to an extensive root system, effective control of evapotranspiration and stomata with an ability to recover rapidly after periods of water stress, and an ability to withstand desiccation. Further, where the growing season is long, the tillering varieties are able to recover to a certain extent from water deficits in the earlier growth periods by forming additional head-bearing tillers. Severe water deficits during the flowering period (2) cause pollination failure or headblasi. T^r resulting yield reduction can be partly offset by additional head-bearing t i l le r '

Sorghum shows a high degree of ftexibiliiy toward depth and frequency of waior supply because of its d rou^t resistance characteristics. When water supply is limited It may be advantageous to spread available water over a larger area. While yield per unit area will reduced, water utilization efficiency for yield will be greater resulting in higher overall production in relation to volume of water supplied. The timing Of supply should aim at reducing water deficits to e minioium during the establish, ment (0), flowering, (2) and early yield formation (early 3) periods.

The primary root system, with little branching, grows rapidly in deep soils to 1 to l o r n . The secondary system starts several weeks after emergence and extends rapidly up to 2 m, depending on depth of soil wetting. The maxtmum depth is generally reached at the time of heading. In deep soils the extensive root system allows additional flexibility in irrigation scheduling. Depending on depth and frequency o f irr igation , 60 percent (less frequent) to 90 percent (frequent) of the water uptake occurs from the first metre o f soil depth. Normally, when sorghum is full grown, 100 percent of the water is extracted from the first I to 2 m (D - 1-2 m). Under conditions when HTm is 5 to 6 mm/day, about 55 percent of the total available soil water can be depleted without reducing water uptake (p - 0.55). Dunng ripening (4) 80 percent can be depleted.

136


4*


Where rainfall is not sufficient and irrigation water supply is restricted , irrigation to attain optimum production should be based on avoiding water deficits during the periods of peak water use from flowering (2) to early yield formation period (3)* Where water supply w ill be limited during the flowering period, water savings can be made without causing additional heavy yield losses by reducing water supply during the vagetative (1 ), late yield formation (late 3) and ripening period (4).

The number of irrigations normally varies between one and four, depending on climatic conditions, and soil texture. The greatest water utilization efficiency will be obtained when these irrigations are well-timed in relation to the sensitivity of the crop to water deficits.

Irrigation is mostly by surface (border, basin or corrugation) method.

YIELD

A good yield under irrigation is 3 .5 to 5 ton/ha (12 to 15 percent moisture). Th* water utilization efficiency for harvested yield (Ey ) for grain is between 0.6 and 1.0 kg/m^

Gram yield under spate irrigation with little or no rainfall, a total growing period of 90 days with ETm - 425 to 450 mm and net depth applied of about 300 mm, is about 000 kg^ha with a maximum cf 1 300 kg/ha.

SOYBEAN

Soybean ( Glvcine max) i » one of the most tmponant •vorld crop* aiMl t* grown for o il and protetn. Present world production i » about 6. 2 mlUion ton* of *eed over 45 million ha. The crop i » mainly grown under ramfed condition* but irr lga iton , specifically *upplemcni«1 irr igation , i* increasingly used.

The crop 1* grown under warm conditions In the trop ics , subtropics and temperate climate*. Soybean is relatively reatitant to low and very hi|^ temperatures but growth rates decrease above 35°C and below In soaieva r ie t ies , flowering may be delayed at temperatures below 24^C. Minimum laoip* cratures for growth are about 10 C and for crop production about 1 j^ C . Only 25 to 30 percent o f the flowers produce set pods, the final number depending on the plant v iM u r during the flowenng period. Y ea r to year temperature varlattons can lead to d ifferences in flowenng.

Soybean i$ basically a short-day plant, but response to daylength vanes with vane ty and temperature and developed var ie t ies are adapted only to rather narrow latitude d if ferences. Daylength has an influence on the rate of development o f the crop; In short-day types, increased daylength may result in the delay of f lowenng and taller plants with more nodes. Short days hasten flowering, particularly for late- maturing va r ie t ie s . Vegetative growth normally ceases dunng yield formation. 1 he length of the total growing period is 100 to 130 days o r more. Soybean ts often grown as a rotation crop in combination with cotton, maize and sorghum. Row spacing va n es from 0*4 to 0 .6 m with 30 to 40 seeds per metre of row.

The crop can be grown on a wide range of soils except those which are very sandy. Optimum soil pH is 6 to 6.5. The fe r t i l iz e r requiremenlj are 15 to 30 kg/ha P and 25 to 60 kg/ha K . Soybean is capable of fixing atmcsphenc nitrogen which meets It* requirements for high y ie ld * . H ow ever , a starter do«.e 'f ’ ' ?(’ V 'v „ ,beneficial for good ea r ly growth.

A shallow water table, pan icu lar ly during the ear ly growth period can adversely affect y ie lds. The plant is sensitive to waterlogging, but moderately tolerani to soil salinity. Y ield decrease due to soil salinity is ; 0% at ECe 5 mmho*'em, 10% at 5 .5 , 231 at 6 .2 , 50A at 7> 5 and 100% at ECc 10 mmhos/cm.

WATER REQUIREMENTS

Water requirements (ETm) for maximum production vary between and TOO mm/season depending on climate and Iwngth of growing penod . The water requirements are given fay the crop coefficient (kc ) in relation lo reference evapotranspiration (E T o ) and kc ISi dunng the initial stage 0 .3 -0 .4 (20 to 25 days), the developmsnt stage " 0 .8 (25 to 35 days), the mid-season stage 1*0-1.15 (45 to 65 days), the la ta -eeeec stage 0. 7-0.8 ( w to JO days) and at berveai 0.4-0.S>

w a t e r s u p p l y a n d c r o p y i e l d

he growth pen od * o f soybean are shown in F lgere 39- The relotHNiship* based on interpreted information on re la tive y ie ld decrease ( I • Y a fY m ) amd

1 3 8

Vt«id Formation IS) lod d «v pod fin0 « ) l ib )

M-40

F ig . 39 \ j f o w U i p e r i o d : * o t :>oybean (a fte r Chiang)

evapotranspiration defic it (1 - ETa/ETm) are given in F igure 40 for total growing period and the individual growth pen ods . (F o r examples see p. 40 and Chapter V I . )

Adequate va te r (between 15 and 50 percent soil water depletion) must be available for germination. Water defic iency or excess water during the vegetative period (1) w ill retard growth. Growth periods most sensitive to water defic its are the flowering (2 ) and yield formation periods (3 ) , particu larly the later part o f the flowering penod (end 2) and early part o f the yield formation (pod development, 3a) period when water defic its may cause heavy flower and pod dropping. Irrigation a fter severe water defic its dunng penod 2 may cause similar symptoms. The seeming

•tunc crop dunng f low enn g (2 ) and early yield formation (pod

I3U

Ui'v tupiiu'-iii , j fu j t - IN*.' t *' su 11 oi tjic J Iv 'w vring p e n w' l c * icik: utg .3v«r one inonth ; •>|;^* w a te r d e fic its d u rin g a p a rt o f th is p e rio d can be compensated fo r by b e tte r re te n tio n o f U te r-fo rm e d flo w e rs and pod se tting . F o r norm al pod f i l l t n t and h ith y ie ld the ootl w a te r d u r in g the y ie ld fo rm a iion period (pod h l l tn g , Jb) should not exceed the 50 p e r cent dep le tion le v e l.

When w a te r supply ts lim ite d , savings in w a te r can be mode by reductng the supply d u rin g the vegetative period ( I ) and p a r t ic u la r ly near c rop m a tu rity Gate £ ). When re q u ire d , a p re - ir r ig e t io n should be given to a llo w p ro p e r c ro p estabtishm ent. W a ier savings should be m inim al d u n n d thr inte flo w e rin g pe rio d Gate 2) and e a rly y ie ld fortnation period (pod developmei

F or maximum production , w ater supply may be d ire c te d tow ard en la rg ing the area under ir r iga t ion rather than toward meeting maximum crop w a te r re q u ire m ^ '” ' o v e r a res tr ic ted a c rea ge . H ow ever , c rop w ater demands should be met d u ru

I .1 - V < , I . V ’

t o o s o s o r o s o s o a o i o i 0> 0

- t ’ Relationship between re la t iv e y ie ld decrease (1 - Y a/Y m ) andrelaiiVC at' " f t r,ii i c ■ i i' ’ . F T « ' f or b<*s'

Deperuling on aotl w a te r a v a ila b ility , e a r ly ro o t development in deep so ils i* relatively rapid and v ig o ro u s . M ost rap id roo t grow th is often noted a fte r the s ta rt o f f lo w e rin g . The top roo t may extend to o ve r 1.5m. The c ro p can e ffe c iive ty d raw a ll a va ila b le so il w a te r up to 1.6 m. If so il depth is re s tr ic te d , the top roo t is less pronounced snd la te ra l ro o ts a re m ore d e v e lo p s . W h ile the cro p con grow on heavy s o ils , the roo ts tend not to penetra te evon m oderate ly compacted la y e rs . A lthough the roo ts a re g en e ra lly concentreAod in dM A ra l 0 .6 m o r even somettmeo the f t r o t 0 .3 m, considerab le so il w a te r, p a ru c u la r ly d u r ta g th e la te r grow th p e n o d s , com be e x tra c ird from the lo w e r p o rts o f the ro o t to n e . H ow ever, under norm al condiuoas lOOperc^

Ai gcrminanon, the soil water content should not exceed 65 percent or fall below 50 percent of available soil water. A fter cstabltshment (0), the crop can withstand short periods of drought. For irrigation scheduling under medium evaporative conditions (ETm 5 to 6 mm/day), an allowable depletion level o f 53per - 3 - ' e assumed (p - 0. 55).

140

1RRIGAiic'N *k,_Hb.L/LLlNG

Soybean is usually not grown under full irrigation. In many climatic conditions, however, one or more supplemental irrigations during crit ical growth periods will substantially increase y ields. U one application can be given, the most likely timing will be in the late flowering period (2), when small pods arc beginning to appear. If two applications can be given, it is usually wise to give the first application at pre-emergence to assure a rapid establishment of the plant. A third application, where possible, will give the best results if giver at the beginning of pod filling (Jb).

IRRIGATION METHODS

In areas soybean is irrigated, ino costs of sprinkler irrigation only canbe borne if it is grown in rotation with high value crops. Furrow irrigation is most common.

YIELD AND Q U ALITY

Yield can vary widely with water availability, fertilization and row spacing. Under rainfed conditions, good soybean yields vary between 1.5 and 2.5 ton/ha seed. High yields of improved varieties are between 2.5 and 3*5 ton/ha seed under irrigation. The water utilization efficiency for harvested yield (Ey) for seed containing 6 to 10 p e r cent moisture is O.Z to 0. 7 /ml. The effect of irrigation on oil and protein content of the grain is rather insignificant. However, under adequate irrigation there is a tendency toward a slight increase in protein content and a slight decrease in oil content.

SUGARBEET

Sugarbeet ( Beta v u lq «r i> ) p ro v id e s about 40 percen t o f the w o r ld 's sugar prcKiuciion. P re sen t world production is about 295 m illion tons o f beets from about 9* 5 m illion ha.

The crop is b e lieved to o r ig in a te from A s ia . Su garbeel is a btennial c rop but fo r sugar production beets a rc h arvested in the f ir s t y e a r . F low er in g o c cu rs during the second y e a r . Th e crop is grow n under ra in fed conditions but a lso w id e ly under ir r ig a t io n in the subtrop ics w h ere the crop is known fo r its high to le ra n ce to sa line and a lka li so ila .

The crop needs a r e la t iv e ly long grow in g p e r io d , norm ally from 140 to 160 up to 200 days . L a rg e amounts o f sugar a re formed m the le a v e s . The g rea te r pari t« used fo r growth p ro c es s es during the veg e ta t iv e p e r io d , w h ile in the la te grow<* p e r iod when v e g e ta t iv e grow th s low s down a la rg e part is stored m the r o o fs , e v e r , sugar y ie ld is determ ined by both root s iz e and sugar con crn tra lton , M rapid growth o f the s to rage root the sugar concentration reach es a steady va lue * 'IS p r in c ip a lly determ ined by c lim a te , w a ter supply and n itrogen le v e l in the so il aM<: ) ' m flu e n c ^ to some extent by va r ie ty and plant spacing. Sugar percen tage in the root IS o ften g re a te r than 15 percen t o f the fresh root w eigh t. The crop is harvested toward the end o f the firs t season 's g row th , when the roots contain manmum amount of sugar.

The crop is grown in d iffe ren t c lim ates. Seed germ ination ts poss ib le at but the e ffe c t iv e minimum is con sidered to be 7 to 10®C. H igh er tem pera ru ret during v e g e ta t ive growth a re p r e fe r r e d , but high sugar y ie ld s a re obtained when ntght tem pe ra tu res a re betw**cr. IS and 20^C and day tem peratures between 20 and 25®C during the la tte r p a n o f the g row in g p e n o d . During th is p en od tem peratures g r e a te r than

g rea tly d e c rea se sugar y ie ld s . F o r high sugar y ie ld s and low vege ta tive growth in the la tter p a n o f the g row in g p e n o d , p ro g re s s iv e ly c o o le r nights should be AGi oTipanicd by an exhaustion o f a va ilab le so il n itrogen and sot) w a ter .

When the crop is grown fo r seed , seve ra l w eeks at low tem pera tu res , near 4®C , a re requ ired to induce r iow erin g , which tends to be acce lera ted by long days.

The crop can be grown on a w ide range o f s o ils with medium to s ligh tly heavy w elU d ra in cd so ils p r e fe r r e d . R cs tn c ted deep root growth in the e a r ly part o f

the grow in g p en od due to so il compaction may resu lt in form alton o f forked and sprangled roots with reduced y ie ld s . So il pH sm aller than 5*S is unfavourab le to grow th . C rust form ing at ihe so i! su rface at the tim e o f germ ination can lead lo poor crop stand.

Adequate o itrogen ta requ ired to ensure e e r ly maximum veg e ta t ive growth. N itrogen is often given in apUt a p p lica tion s , a small amount at p lan tiag and the rest a fte r thinning. N itrogen e ith e r tn an e x c es s iv e amount o r when applied la te du nng the g row in g season reduces sugar content. F e r t i l iz e r app lica tion * au y be up to 1 ^ kg/ha N , to 70 kg/ha P at planting and 100 to I t o kg/ha K .

A d eep , w e ll-p rep a red seed bed ts advantageous. Seada a re plantod 1 to 2 cm deep in s in g le o r double ro w s , with width between atngle row s 0 .5 to 0 .7 m and double row s about 1 m. When the plant has 4 to 8 lo a vea , thtMklngji by hand o r by machine.IS frequ en tly needed to space 3 to 6 beets p e r m etre row . Seed ra te * va ry between12 and 30 kg/ha. P lant d en s it ies under com m ercia l production va ry from 40 000 up to'(V' Oyi .

1 4 2

Exvepi during the early stages, a fte r crop establishment, the crop is tolerant to salin ity. Y le ld d ecrease is 0% at ECe 7, 10% at 8 .7 , 2S% at 11, [30% at 15 and 100% at ECe 2L mmhos/cm. During e a r ly growth ECe should not exceed

W A 4 Lk K EQl iR L M h N T S

For maximum production, water requirements of the crop are related to re ference crop evapotranspiration (E T o ) . The crop coeffic ient (kc) is 0 .^ -0 . 5 during the initial stage (25 to 30 days ), 0 .75 *0 .85 during the crop development stage ( 35 to 60 days ), 1.05- 1.2 during mid-season stage (50 to 70 days ), 0 .9 - 1.0 during the late-season stage (30 to 50 days) and 0 .6 -0 . 7 at time o f harvest. Total water requirements are in the range o f 550 to 750 mm/growing per iod , but vary with climate and length o f the total growing p en od . Time o f sowing affects the rate o f crop d e v e lopment, particu larly from emergence to when the crop has reacfied its maximum height, which fo r an autumn-sown crop may be 1^0 days, (or a spring-sown crop about 90 davs and fo r a late spnng/early summer-sown crop about 60 days.


The duration o f the d ifferent growth periods o f the sugarbeet crop wuh KO to 200 day growing period is shown in F igure C \* The relationship between re la tive yie ld d ecrease and re la t ive evapotranspiration defic it for sucar and boot pro<hirnon is shown for the total growing season in F igure L 'J .

*ul

Growth periods of sugarbeet (a fte r G .B . Heathcots)

143

W h < n g r * . ' + N i ^ g a r , f l o w e n n g a : . p r ^ . ^ ; . . 'Sugarbeet la part icu la r ly seniutive to water dettcita at tne tune ot crop emer^ and a period o f about a month a fter emergence (0 )« Frequent, hghi im g a iK i .^ are p re fe r red dunng this p en o d , and tn ig a t io n may also be needed to r ^ u c e crust formation on the soil and to reduce saltnity ot the top so il. Farlv o ve r -w a te r in g may retard lea f development and can encourage f low en n g during the f ir s t y ea r (bo lt ing ).

W ater de fic its in the middle p a n o f the growing p en od (vege ta t ive and vield formation p e n o d s , 1 and 3 ) terid to affect sugar y ie lds more strongly when occu rr ing during la ter per iods . Ample supply in the la ter p an of the growing period (r ipen ing per iod , 4 ) has an adverse effect on sugar concentration a h h o u ^ it may increase the root s iz e , with the final e ffect on y ie ld being small. W ater de fic its together with a nitrogen defic iency toward the end of the growing period lead to a reduction in root growth but an increase in sugar concentration. IB genera l, top growth toward the end o f the growing period ter^s to be negative ly corre la ted wiUi sugar production. Irrigation supply must be discontinued at least 2 to 4 weeks p r io r to harvest.

! ^ , except during emergence and ear ly growth per iods , it appears that therop IS loss sensitive to mc^erate water de f ic its . The effect o f reduced water supply

ov e r the total growing period is often masked by the overr id ing influence o f temperature, nitrogen availability and reduced water needs during a period just p r io r to harvest.

When available water resources a re limited and when maxtmura o ve ra l l p ro duction IS aimed at, water supply should be d irected toward expanding the area under irr iga tion rather than concentrating the supply ove r a limited area to meet maximum water requirements (F.Tm) ove r the total growing period . This is because there ts sn increase in the e ff ic iency o f water utilization (E y ) for both roots and sugar yield when water supply is reduced so that yield^ decrease less than proportionally with the reduction o f water supply (ky < 1 ) provided the growing environment during the later part o f the growing p e r i ^ is favourable to sugar storage (F igu re 42).

f t f t

ip ivi weea relat. .. .4. a Ym)dative evapotrewspiration deiFictt (1 - ETa/ETm) for sugarbeet

144


In deep so ils (he crop can deve lop a deep tap root system but norm ally ICX) percen t o f the w a te r is ex trac ted from the f i r s t 0 .7 tc ! . 2 m so il depth CD - 0. 7 -1 .2 m) Under conditions when ETm is 5 to 6 mm/day, 30 to 60 p ercen t o f the total a va ilab le •oil water can be depleted without reduc ing w a te r uptake (p - 0 - 5 - 0 . 6 ) , with h igher depletion le v e ls just b e fo re h a rves t . When the plant is under w a te r s t re s s the lea ves become dark green in co lou r and when the w a te r *-rros.« is sevo ro Tho lea ves fa il to recover from midday w ilt in g in the even ing .


Frequent, light i r r ig a t io n s during the establishment p e r iod (0 ) a re advantageous and suffic ient so il w a te r must be ava ilab le at em ergence . An ir r ig a t io n is frequen tly applied a f te r thinning. Ir r iga t ion in te rva ls can be se lected using Tab le 21. The ir r ig a t ion is discontinued at least 2 to < weeks b e fo re ha rves t to in c rea s e sugar concentration in the beets . The so il should, h ow eve r , not be too d ry to hamper l i ft in g o f the beets at h a rves t.

IRRIGATION METHODS

The most common method is fu rrow ir r ig a t io n . B ord er i r r ig a t io n is sometimes p rac t ised but it is not common. S p r in k le r i r r ig a t io n o f fe r s advantages p a r t icu la r ly during the germination and em ergence per iod when frequent but light app lications may be adcQuate. H ow eve r , young plants w il l be damaged when sprink ling with p oo r quality (s a l in e ; w a ter .

YIELD LEVEL

A good com m ercia l y ie ld o f 160 to 2(X) day sugarbeet is < 0 to 60 ton/ha o f fresh Loct at 15 percent sugar. Under ce rta in conditions y ie ld s o f up to 70 to 8 0 ton/ha a re obtained. The w ater utilization e f f ic ien cy fo r harvested y ie ld (E y ) fo r beets containing 8 0 to 8 5 percen t moisture is 6 to 9 kg/m^ and fo r sucrose containing no m oisture 0 .9 to

kg/m>.

A few com parative studies have been made between sugarbeet and sugarcane parformance. F o r a g iven loca tion , c lim ate is the most important fa c to r in d icta ting whlck c rop is l ik e ly to be more suitable from the point o f v iew o f production .

SUGARCANE

Th« present area o f sugarcane ( Saccarum officinarmp) la about 13 million ha v iih a total commercial world production of about 700 million ton/year cane o r SS million ton/year sucrose.

■sugarcane originated in As ia , probably in New Guinea. Most of the rainfcd and irrigated commercial sugarcane is grown betwoan 3 5 ^^ and 5 of the equator.The crop flourishes under e long, warm growing season with a high incidence of radiation and adequate moisture, followed by a d ry , sunny and fa ir ly cool but frosi* free ripening and harveating period.

Optimum temperature for sprouting (germination; ol stem cuttings tt j * to 38®C. Optimum growth is achieved with mean daily temperatures between 22 and 30®C . Minimum temperature for active growth is approximately 20®C. For npening, however, re latively lower temperatures in the range o f 2 0 to 10®C are des irab le , since thia Has a noticeable influence on the reduction of vegetative growth rate and the ennchmeni o f sucrose in the cane.

A long growing season is essential for h i ^ y ie lds. The normal length of the total growing period van es between 9 months with harvest before winter frost to ZC months in Hawaii, but it is generally 15 to 16 months. Plant ( f ir s t ) crop is normally followed by 2 to ^ ratoon crops, and in certain cases up to a maximum of 8 crops ara taken, each taking about 1 year to mature. Growth of the stool is slow at f irs t , gradually increasing until the maximum growth rate is reached after which growth slows down as the cane begins to ripen and mature. The flowering of sugarcane is controlled by daylength, but it is also influenced by water and nitrogen supply.F lowering has a p rogress ive deleterious effect on sucrose content. Normally, there fore , f lowenng is prevented or non-flowering varieties are used.

Sugarcane does not require a special type of soil. Best soils are those that are more than 1 m deep but deep rooting to a depth o f up to 5 m is possible. The aoil should preferably be well-aerated (a fter heavy ram the pore space filled with air > 10 to 1 2 percent) and have a total available water content o f IS percent o r more.When there is a groundwater table u should be more than 1. S to 2.0 m below the surface. The optimum soil pH is about 6 .5 but sugarcane w il l grow in soils with pH in the range of 5 to 8 . 5 -

Sugarcane has high nitrogen and potassium needs and relatively low phosphate requirements, or 100 to AX) kg/ha N , 20 to 90 kg/ha P and 125 to 160 kg/ha K for a yield o f 100 ton/ha cane, but application rates are sometimes higher. At matunty, the nitrogen content of the soil must be as low as possible for e good suger recovery , particulttrlv where the npening penod is motsi and warm.

Row !»pat.tng v a n e s usually between 1. 1 and 1 .^ m; number of s e tsp er ha depends on the number of buds per set and mi^ vary between 2 1 0 0 0 and 3 S0 W .

Sugarcane is moderately sensitive to salinity end decrease in crop yield due . V reusing salinity 1 s : 0% at ECe 1 ^

10.il and 1(X)\ at ECe 18.6 mmhos/cm.

A A i t k IkbMLN 1

Adequate evellebte moi>lur«: ir.rougr.oui me g row in g pervvvi . « .mpor' s t ~ r obiaining maximum yielda because vegetative growth tficludmg cene growth is directly

146

proportional to the w ater transp ired . Depending on clim ate , w ater requirem ents (E T m ) o f sugarcane a re 1 500 to 2 500 mm even ly d istributed o v e r the grow in g season. The crop coe ff ic ien t (k c ) va lu es , re la ting ETm to re fe ren ce evapotransp iration (E T o ) fo r the d if fe ren t growth stages a r e :

Development stages

planting to 0 .2 5 full canopy 0 .25 to 0 .50 full canopy 0.50 to 0 .7 5 full canopy 0 . 75 to full canopy peak use ea r ly senescence ripening

days kc coe ff ic ien ts

30-60 0 .4 0 -0 .6 030-40 0 .7 5 -0 .8 515 -25 0 .9 0 -1 .0 045-55 l. (X )-1 .2 0

180-330 1 .05 -1 .3030-150 0 . 80- 1.0 530-60 0 .6 0 -0 .7 5

Ti r e la t i v e humidity and windDram a Pflpor N o . 24)

W ATT '? V a n d CROP Y IE L D

Growth per iods o f sugarcane are shown in F igure 43. Because y ie ld is formedwhen the crop is m the vecotativo form, rho \-iol3 formiit;on p o r ’O*' v e g e tative growth.

’ » *>•1 <$u»

Growth p en o d s o f su^.ii i c (a f te r Kuyper, \ j

Frequmcy and depth o( irngetton thould v*ry mih growth period* o f the cane. During the establishment parted (0 ) , tncludiag emergence and establishment of young seedlings, light, frequent irrtgaiion applications are p re ferred . During the early vegetative period ( 1 ) the tillerin g is in direct proportion to the frequency e l irrigation . An early flush of t i l le rs is ideal because this furnishes shoots o f e fp ros* imately the same age. During stem elongation ( lb ) and early y ie ld formetton O a ), irrigation interval can be extended but depth of water should be increased. There ts a close relationship between stalk elo.'.gation dunng these perioda end waXOr use, M d adequate water supply is important during this pertod o f active growth when the lengeat intemodes are formed. With adequate supply this penod is reached early and a lsototal csne height ts grea ter. The response o f sugarcane to irrlgatton ts giwoter

‘ 3 ^ than duringpart of the yield formation period O b ), when achve lea f area Is declining and the cropduring the vegetative and early yield formation periods ( I and during the le te r

^ e a i s w s i i i w y s u - s u ■ w i i i i a i a v i t g y w i t w u a g v « M « i w a v « a e o a a e p v e w o o e v

IS less able to respond to sunshine. During the ripening period CA), Irrigation in tervals are extended or irrigation is stopped when it Is necessary to binng the crop to maturity by reducing the rate of vegetative grosrth, dehydrating the cane and forcing the conversion of total sugars to recoverable sucrose. With the check of vegetative growth, the ratio between dry matter stored as sucrose and that used for new growth also increases. During the y ie ld formation penod (3 ) frequent irngatlon has an accelerating effect on flowering, which leads to a reduction o f sugar production.

1 he relationships between relative yield decrease and relative water defu it for the total growing period and for the individual growth penods are shown tn Figure AA. Water deficit during the establishment penod (0) and early vegetative

f ieriod (ttUcring, la ) has an adverse effect on yield aa compared to water deficit in ater growth periods. Water deficit slows down germination and tiU enng and the

number of t il lers is smaller. Water deficit dunng the vegetative penod (stem elongation, lb ) and early yield formation (3a) cause* a lower rale of stalk elongation. Severe w ater deficit dunng the later part of yield formation (3b) forces tha crop to ripen. Dunng the ripening period (A ), a low soil moisture content is necessary. However, when the plant is too seriously deprived of water, loss in sugar coutei be greater than sugar formation.

I ig. Relaiionshtps between relative yteld d<relative evapotranspiration deflcit '

andm) lor sugarcane

148

W hen w a te r supply is l im ited , and apart from o ther con s id e ra t ion s , the a c rea g e can be e n l a r a ^ using w a te r saved du n n g the y ie ld formation p er iod ( 3 ) ; this w il l resu lt in a s l ig h t ly lo w e r y ie ld p e r h ec ta re but o v e ra l l production w i l l be h igher .

W ATER U P T A K E

Rooting depth v a n e s with so il type and ir r ig a t io n reg im e ; in frequen t, heavy ir r ig a t io n s normally resu lt in a m ore extens ive root system . Rooting depth can be up to 3 m but a c t iv e root zone for w a te r uptake is g en e ra l ly lim ited to the uppermost layers. When these la y e rs arc depicted the uptake from g re a te r depth in c rea ses rapidly but normally 1 0 0 percen t o f the w ater is ex tracted from the f i r s t 1 . 2 to 2 . 0 m (D • 1 .2 -2 .0 m). With evapotransp ira tion during the g row in g season o f 5 to 6 mm/day, the depletion le v e l during the v eg e ta t iv e ( 1 ) and y ie ld formation per iod ( 3 ) can be 6 5 percen t o f the total a va ilab le w a te r without having any ser ious e f fe c ts on y ie ld s (p * 0 . 6 ' ) .

IR R IG A T IO N SC H E D U LIN G

When ir r ig a t ion w a te r is not s c a rc e , Tab le 21 can be used to determ ine frequency and depth o f ir r ig a t ion requ ired for a high y ie ld . Under minimum crop w a te r s tress conditions and taking into account the le v e l o f ETm , the depletion le v e l o f the total ava ilab le so il w a ter fo r the establishment p er iod (0 ) is about 30 percen t. Because o f the low dep letion le v e l and a poo r ly formed root system , frequent ir r ig a t ion IS requ ired during this p e r io d . Th is app lies a lso to a ratoon crop because a new root system has to be d eve loped .

During (he v ege ta t ive (1 ) and y ie ld formation (3 ) p e r io d s , the dep letion le v e l ( p ) , depending on ETm , is about 0 .6 5 and frequency and depth o f ir r ig a t ion is v e r y dependent on the w ater holding capac ity o f the soil and the root depth. A low er frequency o f ir r ig a t ion with a h igher application in depth may cause the development o f a d eeper root system prov ided roo t in g is not r e s tr ic ted by la y e rs which a re d ifficu lt to penetra te . During the n p em n g p e n o d (4 ) , a low so il w a ter leve l is requ ired . Ir r ig a t ion w ater is applied only in an extrem ely dry situation but depth o f application IS r ^ u c e d .

W here ir r ig a t ion w ater is limited and ra in fa ll is s c a r c e , ir r ig a t ion scheduling should be based on avo id ing w a te r s t re s s during the establishment p en o d ( 0 ) , fo llowed by the vege ta t ive period (1 ) . H o w eve r , when ir r ig a t io n w a te r is s ca rce during per iod( I ) , the reduction m the hon ch t o f c a n r ' t can be pa rt ly regained in the y ie ld formation penod (3 ).

IR R IG A T IO N M E TH O D S

Furrow ir r ig a t ion ts most commonly used and is p a r t icu la r ly e f fe c t iv e fo r e a r ly plant c rop . In la te r c rop growth p e n o d s and during ratoon c ro p s , the w a ter d is tnbu tion may become in c reas in g ly problematic because o f d e te r io ra t ion o f the fu rrow s . Reduced furrow length is sometimes used to a llow better d ts tn bu tion o f wAtrr c^ver the fie ld in a la te r stage.

A recent trend i * in the d irec t ion o f sprink ler and drip .t ? t c rs p n n k le r im g s t t o n , in creas ing use is made o f spray guns, hand and automatically

14V

moved, replacing the cumbersome boom and labour-intensive hand-moved sprinkler laterals. P reva iling winds of more than L o r S m/see will limit iheir usefulness. An optimum combination o f distance between field roads for harvesting and for moving guns with different spray length must be analysed. Dnp trrigslton using double wall drip lines has been successfully employed particu larly in K sw a ii; replecement of burned drip lines after harvest is compensaietl •. r ,- ' ’ labourcost.

Y IELD LE VE L AND Q U A L IT Y

Sugar yield depends on cane tonnage, sugar content of the cane and on the cane quality. It is important that the cane is harvested at the most suitable momeni when the economic optimum of recoverab le sugar per area is reached. Cane locinage at harvest can vary between 50 end 1 5 0 ton/ha o r more, which depends p er t icu la r^ ot the length of the total growing period and whether it is a plant o r a ratoon crop. Cane yie lds produced under rainfed conditions can vary greatly . Good yields in the humid tropics of a totally rainfed crop can be m the range of 70 to 10 0 ton/ha cane, and in the dry tropics and subtropics with irr igation , 110 to 150 ton/ha cane. The water utilization efficiency for harvested yield (E y ) for cane containing about 6 0 percent moisture is 5 to 8 m) and for sucrose containing no m oisture0 * 6 to 1 . 0 kg/m*, both with the highest values for good ratoon crops in the subtropics.

Toward maturity, vegetative growth is reduced and sugar cOtttMt o f the cane increases greatly . Sugar content at harvest is usually between 10 and 12 percent o f the cane fresh weight, but under experimental conditions l 8 percent o r more has been observed. Sugar content seems to decrease slightly with increasetl cane y ie lds. Luxurious growth should be avoided during cane ripening which can be achiovod h y low temperature, low nitrogen level and restricted water supply. With respoct to mice purity, this is positively affected by low minimum temperatures several weeks before harvest.

SUNFLOWER

o I : ^. t a ^ r aiiuu-. r- -T.j;...atO' ircai ^^uira. aau uorlh America. Lately Its importance as an oil crop has grown and at present it is the second most IMportant o il crop next to soybean. Total annual world production ts some 10 million tons of seed from some 9 o milhon ha.

Sunflower thrives m climates ranging from and under irr igation to temperate under rain/ed conditions, but is susceptible to frost. Mean daily temperatures for good growth are between 18 and 25®C. The total growing period van es from 70 days in parts o f Russia where the season is short to 200 days at higher altitudes m Mexico, In the subtropics under irrigation the total growing period is about 130 days. For temperate c I imates the optimum planting date for early as well as late maturing varieties is between late spring and early summer. Delay in planting results in shortening of the vegetative penod and early maturity, causing a decrease in head diameter and seed weight. Sunflower is a short-day plant with a variable response todaylength , but day-neutral varieties exist.

The crop is mainly grown under ramfed conditions on a wide range o f so ils .L tiUcr erratic and low ra in fa ll, a rather deep soil with good water holding capacity ts required. Due to its deep root system (2 to 3 m) soil water can be explored at great depths. Optimum soil pH is in the range of t»,() to 7 .5 , but at lower values liming may be necessary. F e r t i l iz e r application is in general 50 to 100 kg/ha N , 20 to 43 kg/ha P and 60 to 125 kg/ha K. The crop is particu larly sensitive to boron defic iency.

Optimum plant density is about 6 0 00< plants 'ha with row spacing of about0 . 9 tn ; seed rate » “ between L And 10 kc 'ha . lU-'th t ran "T'lanMt :cr. and -I, rr.-r vw'are practised.

In the major sunflower growing areas salinity problems are minor; an iUu.vJtion o f tolerance to salinity during crop establishment ts shown by the emergence

“ at 4. 3, 30 to 6 0% at !: la ter growth periods

i l « W 4 V * J V 4 W I I V I a w s ^ a w i a ^ ^ x a a v a ^ w t i 1 9 !

oerccntage of seedlings which is 8o to 100"» at ECc 0 , 70 to 755» at 4. 3, 30 to 60% at 9. 3, 15 to 55 10 and 0 to 2j% st ECe 13 mmhos/cm. However, insunflower is moderately tolerant to salinity

W ATER REOIMREMENTS

I he water requirements ol sunflower vary from 600 to 1 IKK) mm, depending on climate and length of total growing period. Evapotranspiration increases from establishment to flowering, and can be as high as 12 to 15 mm/day. High evapotranspiration ra les are maintained dunng seed setting and ear ly npening penod . P ercen tage of total crop water use over the different growth pen<^s is about 2 0 percent dunng vegetative penod, 55 percent dunng the f lowering period and the remaining 25 percent dunng the yield fortnation and ripening penods. The crop coefficient (kcj ts 0.3*0.4 dunng the initial stage (20 to 2 5 days ), 0 . 7 -0 . 8 during the crop esiablishmeot stage OS to 40 days), 1»0S*1*2 dunng tha mid-season stage (40 to 50 days), 0.7-0.8 dunng the laie-season stage (25 to 30 davsi and o 1 ,it rn.**” nT . '■r irvest.

WATER S U P P LY AKD CROP Y IELD

In respect of total yield produced, water requirements o f sunflower are vompared to most crops. Despite its high water use, the crop has an

151

atnluy lo withatand abort penoda o l a « v « r « aoil w « t « r dalic it o f up to 1 3 atmoaphere tension. Long parioda of aavara aoil v a ta r daftcu at any growth panod cauaa laaf- drying with aubaaquent reduction in aaad ytald. With heavy ram o r irrigation following an extremely dry p en od , only a p a m a l recovery occura.

The duration o f the different growth penoda o f a 140-4m crop la ahown in Figure 43* The relattonahtpa between rrT,i* v<* yield decroaae O • Ya/Yai) and re la t iv e cvapotranapiration deficit ( 1 -I .1K ' 11.1M v'” t' • 1 V' ' 1 *i ! r \ ’

m) are ahown in Figure 46. For

o

>• • t I » o — . . ' U a ; r> « • • < * • > r « • • p *

Fig. 43 Growth periods o f aunflowci

IT*

Fig. 46 Relationabip between relative yield decreaae (I - Ya/Ym) andrela!:\ r -i* i..r. t ♦ FT , M T - '

15Z

Severe water deficits dunng the early vegetative period ( l a ) result in reduced plant height but may increase root depth. Adequate water during the late vegetative period is required for proper bud development (,1b). The flowering penod (2 ) IS the most sensitive to water deficits which cause considerable yield decrease since fewer flowers come to full development. Y ield formation (3 ) is the next most sensitive period to water de fic it, causing severe reduction in both y ie ld and oilcontent,

in deep soils the root system of sunflower may extend up to 2 to 3 m but normally, when the crop is full grown, 1(X) percent of the water is extracted from the first 0 .8 to 1-5 m (D - 0.3 -1. 3 m). Under conditions when maximum evapotranspiration is 3 to 6 mm/day, the water uptake is a f f ec ted when about .13 p e r c e n t o f the total able sotl water is depleted (p • O ./ jY


For high production, soil water depletion should not exceed percent of the available soil water, particularly during the late vegetative, flowering and y ie ld formation periods. Due to the deep root system, 2 to i heavy irrigation applications are usually sufficient when the crop is grown on deep, medium textured soils. In addition a pre-irr igation ts given when required. Application should be scheduled during the late vegetative ( lb ) and the flowering (2) periods. When water supply is limited, water savings can be made during the ripening period (/).

IRRIGATION METHODS

The crop is most suited to surface irrigation, particularly by furrow irrigation allowing infrequent and hea\'v application.

YIELD AND A L T >

The giant varieties , grown for poultry feeding and human consumption because o f their low oil content, produce seed yields in the range of 0.8 to 1 .3 ton/ha under rainiad conditions. The seeds of dwarf and semi-dwarf varieties contain 23 to 33 percent oil and give a total y ie ld similar to the giant varieties . New Russian varieties with seeds of low hull content have an oil content of up to 30 percent. Under i rrigation seed yields of 2 . 3 to 3*5 ton/ha are commonly obtained. The water utili/.a- iion effic iency fo r harvested yield (Ey ) for seeds containing 6 to 10 percent moisture IS 0 .3 to O o kg/m^.

TOBACCO

Tobacco (Nicotiiuta tabacum) i » baliavtd to hav« ongtnatad from America. Present world production is about 5*7 million tons o f leaves fromm1111 o- hn .

1 t.o V I vfli. be Uivn.u*».i lo lhem et ...o : ..Mib.g -'.eflue, f i r e , a ir or sun-cured. In general, the dark-coloured air and ftre-cured tobacco IS used for pipe and cigar tobacco, whereas the light-coloured flue and sun- cured IS used for cigarette tobacco.

Tobacco IS grown under a wide range of climates but requires a fros t- free period of 9 0 to 1 2 0 days from transplanting to last harvest of leaves, ^ itm um mean daily temperature for growth is between 20 and 30®C A dry period is required for ripening and harvest o f the leaves. Excess rainfall results in thin, l igh tw e i^ t leaves. Sun-cured or oriental tobacco requires a relatively dry climate to develop Its full aroma. Except for some short-day var ie t ies , cultivated tobacco is day- neutral in Its response to flowering.

A light, sandy soil is required for flue-cured, light tobacco. A ir -cu red , dark tobacco IS grown on silty loam to clay loam soils , while fire-cured and a ir-cured, light tobacco is mostly grown on medium texlured soils. The crop is sensitive to waterlogging and demands well-aerated and drained soils. The optimum pH ranges from 5 to 6 .S. Quality o f the leaves is affected by soil salinity. Depending on the type o f tobacco, fe r t i l iz e r requirements v ary and in general are ^ 0 to 00 ag/ha N ,JO to 90 kg/ha P and 50 to 1 1 0 kg/ha K .

Tobacco is sown on seed beds and is transplanted! .:.0 to 00 days after sowing when the plants arc about 15 cm tall. During the first weeks the seed bads are often covered to protect the young seedlings against unfavourable weather. Spacing after transplantation van es with variety and is generally between 1 . 2 to 0 . 9 * 0 . 9 to 0 . 6 « * Crop rotation after one o r two seasons is recommended with crops such as grass, sorghi:nn, m lle t and maize that are not susceptible to root eelworm.

. produce high value leaves, topping (removal o f flower buds) and desuchertaR(removal of side shoots) is often practised. Time and height of lopping depeade on iho type o f tobacco but is usually dor.** who*" ’ i-'** their K id<flower.

W A TE R REQUIREMENTS

The water requirement* (ETm ) for maximum yield vary with climate and leneth of growing penod from AGO to 600 nua. Dunng the first waahs after emergence in the seed bed the seedlings require J to 5 Utres/m^ daily. A fte r 30 to dO deys the see-^'-'-j receive less water so as to obtain a more mbnat plant. A fte r iO lo 60 thelings are transplanted and the crop is harvested 90 to 1 2 0 days a fter treneplentir^The penod of maximum water requirements occurs 50 to 70 deys after treaepUnting and IS followed by a decrease in water requirements.

The crop coefftcieni Otc) relating crop water r e q u i t r n e j . ; » * -•« ; c.c r c t . . rcvapotranspiretion (E T o ) for the different development stages after ^ e n »U n tu ig are : during the initial stage 0 . 3 -0 *^ ( 1 0 day#), the dev# 1 opment stage *

! ^4

rhe m id-teaaon stage 1 .0 -1 .2 (30 to 35 davs ) during ihc la te-scason stage 0 .9 -1 .0 <30 to 40 days ) and at harvest O.75-O.0T,


The growth periods o f tobacco a re shown m F igure 47. The relationships between re la t ive yield d ecrease (1 - Ya/Ym) and re la t ive evapotranspiration( I - ETa/ETm) arr civcn in F igure 4.8. Fo r calculat'^''^ oxflmplo'i soo p. 40 and Chapter V I .

► I I L O

wppa' leaweeto Kp.vooi

iptait.o tit i v.ot« *o.tn«t.on tl>

' ty n a t # ( t « l M l

M - *• 4«f« I ••y* _ J

F ig . C 7 Growth periods in tobacco (Lu cas )

' he water regimes from which a hiU crop o f tobacco can be obtained vary from • tc to ! soil water, ra in fa l l , supplemental tm ga tton o r full tm g a n o n . Careful water scheduliag ta required because too frequent irrigation damages the crop. Water dwikctis In certain periods may incraase yie lds and it ts recommended practice to eub|6Ct aeedlings during the establishment penod (0 ) p n o r to transplanting to a period o f aioderate water defic it to increase thetr drought resistance* A lso , moderate water d e f ic i ts during the e a r ly vegetative period ( l a ) may enhance root development*

1S5

Moderate water deficits during the f i r s t 20 to 30 days after tranaplanttng have httle effect on final yield but cause temporary retarded growth; however, the crop recovers rapidly with subsequent t rn ge t ion s . In most ca tes , final yields may be lurgcr compared to a crop rece iv ing full irnge iton throughout this growth penod ( l4 ) «

Water defic its during the mid-vegetative penod (rapid growth, lb ) result in reduced growth and smaller leaves. Severe water deficits during the yield formation and ripening periods (3 and 4 ) affect leaf weight and chemical composition which in turn affects the fire-hold ing capacity. However, a mild water deficit dunng npening (4) is desirable to restrict growth of new young leaves.

Excess water results in leaves o f low quality. Heavy ram o r im ga tton may cause *wtlting ', ’ wet feet' or 'drowning'. Waterlogging for two o r more days genera lly severe ly damages the crop and may kill the plants.

To obtain maximum to ta l production under Umitcd water supply, management should be d i r e c t e d t o w a r d s in c r e a s in g the a r e a and p a r t i a l l y m ee t in g the crop water rcq u i remcnt-«i r a t h e r than m ee t in g full c r o p w a t e r r e q u ir e m e n ts o v e r a l im ited a r e a .

Fig. 48 Relationship between relative y ie ld decrease (1 - Ys/Ym> andrelative evapotranspiration deficit ( 1 - ETa/ETm) for tobacco

WATER U PTA K E

Tobacco has a well-developed top root with extensive Konxonial lateral roots. Normally 75 percent of the water uptake occurs over the first 0.3m and lOOpercoBl over the first 0 .5 to 1.0 m CD - 0. 5 - 1 *0 « ) • Root development ts enhanced oy wtth* holding water supply dunng early vegetative period ( la ) . Also topping and desuckennR will favour root development. Full rooting depth ts reached some 40 to 50 days after transplanting. Under conditions when ETm is 5 to 6 mm/day, water uptake will be affected when 5 0 to 60 p e r c m i rhr »otal available soil water has b ew depleted (p • 0.6).

Water must be supplied daily to the young seedlings in the seed bed (0 ) even when evapotranspiration is moderate. At the end of the seed bed penod (0 ) water is withheld for a few days. Immediately before and during transplanting water is supplied to the plants individually to help them through the first weeks a fter transplanting. During the rapid growth period ( lb ) , water should be supplied frequently. During the ear ly 3rie!d formation penod (3 ), at flow enng, few deep irrigations may be sufficient to obtain optimum inelds o f high quality. When water is limited, water should be applied at transplanting, dunng the penod o f rapid growth ( l b ) , and during the early yield formation penod (3 ).

156

IR R IG A T IO N S C H E D U L IN G

IRRIGATION METHODS

Surface and sprinkler irr igation are mostly practised. The quality o f the waior is important in se lecting the most suitable irr igation method, e . g . sprinkler Irrigation should be avoided when only low quality water is available.

Y IELD AND Q U A L ITY

Normally 18 to 22 leaves are harvested with 2 to 3 leaves per week for 30 to 5 0 days. Occasionally, when half the leaves have been harvested and i f the remaining leaves show a uniform ripening, the whole plant is harvested, thus saving labour.Good yields under commercial production with adequate water supply arc in the range o f 2 to 2.5 ton/ho of leaves. The w a te r utilization efficiency for harvested yield (Ey ) fo r cured leaves containing about 10 percent moisture is O.A to 0 . 6 kg/m^.

Irrigation p ractices together with cultivation p ra c t ic es , e .g . topping, and soil fe rt i l ity affect leaf quality. Nicotine content of the leaf is generally 1 . 5 to 2.5 percent o f dry lea f matter for the flue-cured tobacco and 3 to < percent for the air-cured tobacco. Tobacco grown under dry conditions frequently has a dark, small leaf which is dull in colour and lacks elasticity. However, it has a high nicotine content. Under adequate water supply the leaves are thinner and more e lastic , and also the colour is improved, while the nicotine content is optimal. O ve r - irn ga t ion , particularly during the latter part of the total growing peinod results in in fer io r leaf quality.

TOMATO

Tomato (l^copcrs icon ejgulentum) t* the second most important vegetable crop next to potato. Present world production is about A1 million tons fresh fruit from 2 miUion ha.

Tomato i* a rapidlv gro wing crop with a growing penod of 90 to 150 days*It IB a daylen^h neutral plant. Optimum mean daily temperature for g rowth ta 18 to 25®C with night temperatures between 10 and 20®C. Larger differences between day and mght temperatures, h o w e v e ^ adversely affect yield. The crop is very sensitive to frost. Temperatures above 2d C, when accompanied by high humldti|r and strong wind, result m reduced yield. Night temperatures above 20°C accoo^aotad fay high humidity and low sunshine lead to excessive vegetative growth and ppor fruii production. High humidity leads to a greater incidence of pest* and diseases and fruit rotting. Dry climates are therefore preferred for tomato production.

Tomato can be grown on a wide range of soils but a well-dra ined, l i j^ l loam soil with pH of 5 to 7 IS p^refcrred. Waterlogging increases the incidence o fd iscaaes such as bacterial wilt. The fe r t i l iz e r requirements amount, for high producing var ie t iea .io 100 to 150 kg/ha N , 65 to UO kg/ha P and 160 lo 240 kg/ha K.

The seed is generally sown in nursery plots and emergence la within 10 days. Seedlings are transplanted in the field a/ter 25 to J5 days. In the nursery the row distance is about 10 cm. In the field spacing range* from 0.3/0.6 x 0.6/1 m with a population of about AOOOO plants per ha. The crop should be grown in a rotation with crops such as maize, cabbage, cowpea, to redyce pests and disease infestations.

The crop is moderately sensitive to soil saltnlty. Yield decrease et venous ECe values is ; 0\ at ECe 2, 5 mmhos/cm , 10% et 3. 5, 23% et 5.0, 50% at 7.6 and 100% at ECe 12.5 mmhos/cm. The most sensitive penod to salinity is dunng germination as early plant development, and necessary leaching of salts is therefore frequently practised dunng pre-inrlgation or by over-watcnng dunng the tninal im ge t ion application.

WATTP REQUIREMENTS

1 otal water requirements (ETm) after transplanting, of a tomeso crop grown *•* the field for 90 to 120 days, are AOO to 600 mm, depending 00 the c 1 laaoe. I fa ter requirements related to reference evapotranspiration (E T o ) in mm/penod are given by the crop factor (kc) for different crop development stages, o r t dunng the initial stage O.A-0.5 (10 to IS days), the development stage 0. 7-0.8 (20 to 30 days), the aid-season stage 1.05-1.25 (30 to AO davs), the latc-scason stage 0 .8 -0 .9 (30 to AO 4 «y * ) and at harvest 0 .6-0.65.


The plant produces flower* froa bonoa to top dunng the active d e v e lo p a M o i the stao. F ru its can be harves ted w h ile the plant is still flowering et the top. Some- t iaes three flowenng penods related to three harvests can ha d ietia^ishad. Howower, for aarhoniral harvasttng whara tha fruit* are used for to M lo p M « , aaly oao ptchiag

158

i « made. Water supply needs to be adjusted according to the use of the product, e .g . for salad or paste.

Highest yields of salad tomatoes are obtained by frequent, light irrigation. Where mechanical harvesting is used, heavy, infrequent irr igation is more appropriate with the last irrigation applied long before harvest.

The growth penods of tomato for the first harvest are:

0 establishment (m nursery)1 vegetative2 flowering3 yield formation4 ripening

25-35 days 20-25 20-30 20-30 15-20

100-140

For subsequent harvest periods, 2, 3 and 4 will overlap and an additional 20 to 30 days are required for each harvest.

The relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ETm) is given m Figure 49- The crop is most sensitive to water deficit during and immediately after transplanting and during flowering (2) and yield formation (3). Water deficit during the flowering period (2) causes flower drop. Moderate water deficit during the vegetative period (1) enhances root growth.

ft10 OS OS or OS 03 04 09 02 01 0|0

O'

02

^ m t03

0*y09

OS/

07

• OS

09 rm- t>0

0

01

02

0304

09

05

OT

OS

OS- a

to

Fig. 49 Relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ETm) for tomato

For high yield and good quality, the crop needs a controlled supply of water OM the growing penod. Whereas under water limiting conditions some water

savtngt may be mode dunng the vegetative (1) and npemng (4) penods, water eupply should preferably be directed toward maximizing production p e r ha ratl.er than extending the cultivated area under limited water supply.

159

W AT E R U P T A K E

The crop has a fa i r ly deep root system and i n deep so ils roo ts penetrate up to some l .S m . The maxtmum rooting depth is rcachad about 60 d ^ s a fte r transpUntinR. O ver do percen t o f the total w ater uptake occu rs tn the f ir s t 0*5 to 0 *7 m and 100 p e r cent o f the w ater uptake of a full grown crop occurs from tha f ir a l 0 .7 lo 1 .5 m (D •0 . 7 - 1 .5 m ). Under conditions when maximum evapotranspiration (ETm) la S to 6 mmf day, w ater uptake to meet full crop w ater requirem ents is a ffected when m ore then CC percen t o f the total ava ilab le so il w a ter has been depleted (p ■ 0 ./ ).

IR R IG ATIO N SCH ED U LING

The crop perform ance ts sen s itive to the irr iga tion p ra c tic es . In genera) a prolonged sev ere water d e fic it lim its growth and reduces y ie ld s which cannot be co rrec ted by heavy w atering la te r on. H ighest demand fo r w ater is dunng flo w en n g . H ow ever, w ithholding im g a t io n dunng this period is sometimes recommecvdad to fo rce less mature plants into flo w en n g in o vd er to obtain uniform flow erin g and rirrn<r.;. C are should be exerc ised in this to avoid damage to the mature plants.

E xcess ive w atering during the flow en n g period (2 ) has been shown to in crease flow er drop and reduce fru it set. A lso this may cause ex cess ive vegeta tive growth and a delay m ripen ing. W ater supply during and ^ t c r fru it set must be liatitod to a rate which w ill preven t stimulation o f new growth at the expense o f fru it development.Heavy, irregular irrigations o r dry periods alternating with wet periods should be avoided. F o r production o f salad tomato with more than one h arves t, the crop flou rishes best under ligh t, frequent ir r iga t ion , w e ll-d is tr ib u ted o v e r the grow ing period with the sotl depletion le v e l dunng the d ifferen t growth p en od s remaining below percen t (p < O.A). This prom otes optimum growth dunng the total grow ing period and resu lts in high y ie ld o f good qu ality . WiUi one harvest uniform npen ing iH requ ired and the depletion leve l dunng this period may in crease lo 60 to 70 percen t.

When w ater supply is lim ited , application fo r a salad crop can be concentrated dunng p en od s o f transplanting, flow en n g (2 ) and jacld formation O ) . F o r a crop grown fo r paste production, a more extensive irr iga tion mav be applied with last heavy irr iga tion applied p n o r to flow erin g .

IR R IG ATIO N M ETHODS

Surface irr iga tion by furrow is commonly p rac tised . Under sp n n k ler im g a t io n the occu rrence o f fungal d iseases and possib ly bacten a l canker tbay becomo a ma|Dr problem . Fu rther, under sp rin k ler, fruit set may be reduced with an incraaao tn fm it rotting. In the case o f poor quality w a te r, lea f bum w ill Occur with apnnkUtr t iT tM * tion; this may be reduced by sprinkling at night and shifting o f sp r in k le r Unoa wltn the d irection o f the p reva ilin g wind. Due to the crops apeciftc demands fo r a aoilw ater content achieved V a f wet? ■' c . » n .-He r r drip ir n caiicn has beensuccessfu lly applied.

Y IE LD AND Q U A L IT Y

Frequent light irr iga tion s unprove the s is e , shape, ju iciness and co lou r o f tiie fru it, but total solids (d ry m atter centnnt) and acid contani w ill be reduced. However,ihe decreft*r viU lower the fruit qualitv for processing. In selecting the

160

irr igation practices consideration must therefore be given to the type o f end product required. Prolonged water defic its durmg the yield formation period (3) interrupted by heavy irr iganon leads to fruit cracking. Where fruit rot is a problem, frequent sprinkler irr igation should be avoided during the period o f y ield formation.

A good commercial y ield under irr iga t ion is ^5 to 65 ton/ha fresh fru it , o f which 80 to 90 percent is moisture, depending on the use o f the product. The water utilization e f fic iency for harvested yield (E y ) fo r fresh tomatoes is 10 to 12 kg/m*.

WATERMELON

Watermelon ( C > t r . v. - : yv-kiLL!*) *• nati g c ;;.c t , at g >.• : i otM v « . ai..: ^. tropical A fr ica south of the equator. The crop can survtve the d e se rt cUaMtt when fjroundwater is available and the fruit sometimes serves as a so urce of w ater fo r ll consumption. World production is about 23 million tons fruit from l .d million ba.

The crop p re fers a hot, dry climate with mean daily tcinparaturcs o f 22 to 30*^C Maximum and mmiinum temperatures for growth are about 35 and 104C raapacitvaly. The optimum soil temperature for root growth is in the range of 20 to 35^^* Fruits grown under hot, dry conditions have a high sugar content of 11 percent in comparison to 8 percent under coo l, humid conditions. The crop is very sensitive to frost. The length of the total growing penod ranges from 60 to 110 days, depending on climate.

The crop pre fers a sandy loam soil texture w ith pH of 5.8 to 7.2. Culttvetion in heavy le x tu r ^ soils results in a s low er crop davelopment and cracbad fruits. For high p r^ u c i io n fe r t i l i z e r requirements are 60 to 100 kg/ha N , 25 to 60 kg/ba P and 35 to 80 kg/ha .

The crcp 1 ;iioutTately seuMi < w t •.ouiuiv . i iViii i,. i la -.c i..' t ;itappears to be similar to that of cucumber, o r : 0\ at ECa 2 .5 mmhos/cm, W at 3-3,25% at Z .A , 50% at 6 .3 and 100% at ECe 10 mmhos/cm.

Watermelon is normally seeded d irectly in the fields. 1 htnning la pracitaed15 to 25 days a fter sowing. Spacing between plants and rows v a n e * from 0 .6 x 0 .9 to 1.8 X 2 .A m. Seeds are sometimes placed on hills spaced 1.8 x 2.Z m. In areas prone to fros t, sowing time is dictated often by the occurrence o f frost; sometimes black plastic mulch is used for frost protection.

WATER REQUIREMENTS

Under conditions of high evaporation, irrigation intervals may b o o * abort at 6 to 8 days. For maximum production the crop coeffic len is (kc ) relating water raqiura- ments (ETm) to re ference evapotranspiration (E T o ) a re : during Ihe 10 lo 20 day inlital stage, O.Z-O.S( during the l 5 to 20 days dcvelofMncnt stage, 0 . 7*0 . 8 ; the 35 to 50 day mid-season stage 0 . 95- 1 -03; and the 10 to 13 day taie-aeaaon atage, 0 . 8-0 .9* A fter 70 to 105 days, harvest, kc is 0 .6 5 -0 .75< Water requirements for the total growing period for a 100-day crop range from AOO to 600 mm.

'Jk'ATT-p AVD rp o r ''IFTr*

ihe wrop can deplete »o ii water to a aoil water lenatoo o f o ver 2 anmiagbetwa without the yield being affected. Im gac ien ahould lake place whan, depending on the level o f evaporation, the soil water has been depleted some ^ to 70 percent of available soil water. In dry climates with moderate evopcranoa and l l t l le rain the watermelon produces an acceptable yield (15 ton/ha) with one heavy irrigation in the bemnning of the growing period when soil water o ver the full root depth ts brought to h ^ d capacity.

Tha growth penod a o f a 80 lo 110 day w a iem e lon are ; the eatablishmoni nenod ( 0) o f 10 to 15 doyai the vegecatsve penod ( 1 ) o l 20 to 2Sd aya , me luding e a r ly Clo)

and late vegetative growth ( vine development, lb ) ; the now enng penod o f IS to 20 d*vs* yield formation (fruit fi l l ing, 3) o f 20 to 30 days and ripening (A )?5 to 20 davs The usually has L fruits per plant, which is controlled by pruning practices and harvest date depends on the number of fruits per plant and on uniformity of ripening/

The relationship re lative yield decrease and re lative evapotranspirationdeficit IS given in Figure dO. W ater deficit during the establishment p e r i ^ (0 ) dclav^

_ X J ------------ \--------e a l . r v * U / K ^ n d e f l T l t J . L _ * J 1 ---e, -------- - \\J f

; ; ; ; ^ ' i i 3 p r o < lu c e s ‘’a less vigorous plant. When water deficit occursdunng the earl;• V x produced which causes yield reduction. The

^ t t. \ -L - n i-v*------ _ J• ,refttmttve penod Cle), less leaf area ____U te vegetative period (vine development, lb ), the flowering period (2) ^ d V h e 'v ie ld formation period (fruit filling, 3T are the most sensitive periods to water deficit Dunng the ripening penod ( i ) a reduced w ater supply improves fruit ouahtv. Yields are httle affected by water deficits immediately p r io r to harvest.

ClbfTm09 08 QT 06 oa 04 05 OJ 01 0

. a.rtto

*avtdwe

or

os

lO

Relationship between relative yield decrease (1 - Ya/Ym) and relative evapotranspiration deficit (1 - ETa/ETm) for watermelon

Whereas under limiting conditions some water savings may be made durmc vegetative (1) and npening (d) per iod*, water supply should be directed toward maxuaizing production per ha by meeting full crop water requirements raiher than extending the cultivated area under limited supply.

WATER UPTAKE

J^ater uptake van es with soil type and irrigation practices. The root system can b*r deep and extensive up to a depth of to 2 m. The active root zone where moat of the water is abstracted under adequate water supply is Umucd to the first UO to 1*5 CD • K O - l -S m ) . Under moderate evapoiranapiration (ETm is 5 to 6 mm/dav), th cfop cea d »U te the available soil, water up to ^ o r 50 percent before HTm is affected

0.4-0.5)*

IM

IRRIGATION SCHEDVtmC

Where eveporetion is high and rainfali is low, frequent irrtgatton with en interval from 7 to 10 days may be necessary. Irrigation under dry conditions must be scheduled at the start of the growing period (pre-irrigation), dunng the late vegetative penod (vine development, lb), the nowenng penod (2) and the yield formation period(3). In these periods soil water depletion must not exceed 50 percent. During the npening peric^ (4) relatively dry soils are preferred to increase sugar content an.l avoid the flesh becoming more fibrous and less juicy.

Under moderate evaporation and deep soil with some ram dunng the growing season, v 'm jn iion 'nay be suf^vir’ r to bnng H*' r ' r r

IRRIGATION METHODS

The most common method is by furrow. Under conditions where crop water requirements are high and the soils are light textured, drip irrigation has been succcaafuUy applied with a reduction m overall water demands. The crop has been grown successfully under spate or flood irrigation on banns with one epplicetion of 250 10 350 mm and Uttle or no rainfall and with farmers' yields of about 12 ton/he with a maximum of 20 ton/ha.

i i L L L ANU qJU AL l i )

Within certain water deficit limits, irrigation practices do not greatly affect the number of fruits per plant but affect the fruit size, shape, weight and quality. Ample water suppl v during the ripening period (4) reduces the sugar content arvd adversely affects the flavour. Severe water deficit in the ripening panod on the other hand causes cracked and irregularly-shaped fruits.

A good commcrcual yield under irrigation is 25 to 35 ton/ha. The water utilization efficiency for harvested yield (Ey) for fresh fruits containing about 90 percent moisture vanes between 5 »nd 8 kg/mL

WHEAT

Breo<i and durxim wheat (Triticum aestivum and T . turgidum) w ere domesticatedin the N ear and M iddle East. P reso r t world product ion 1* ahoui .120 million Ton< from 325 million ha.

The crop is grown as a rainfed crop m the temperate c lim ates, in the subtropics with w in te r ra in fa ll, in the tropics near the equator, in the highlands with altitudes of more than 1 500 m and in the trop ics away from the equator where the rainy season is long and where the crop is grown as a winter crop.

Wheal IS grown under irr igation in the trop ics e ither m the highlands near the equator and in the lowlands away from the equator. !n the subtropics with summer rainfall the crop is grown under irr igation in the winter months. In the subtropics with w in ter rainfall it is grown under supplemental irr iga tion .

The length o f the total growing period o f spring wheat ranges from 100 to 130 dqya while winter wheat needs about l80 to 250 days to mature. Daylength and temperature requirements are key factors in v a r ie ty selection . V a r ie t ies can be grouped as w in te r o r spring types according to chilling requirements, w inter hardiness and daylength sensitiv ity . W inter wheat requ ires a cold period o r chilling (verna liza tion ) during early growth for normal heading unde-, long days. W inter wheat in its early stages o f development exhibits a strong resistance to fros t , down to - 20^C. The resistance is lost in the active growth period in spring and during head development and flowering periods frost may lead to head s te r i l ity . Because o f this sometimes more damage is done to the w in te r crop by spring frost than by w inter frost.

In areas o f severe w in ters , cold winds and litt le snow, spring wheat va r ie t ie s are grown. Spring wheat does not require ch illing for heading and i! is day-neutral. H owever, it is also sensitive to fros t. For winter and spring wheat minimum daily temperature for measurable growth is about Mean daily temperature for optimumgrowth and i iU en n g is between 15 and 20®C. O ccurrence o f (spr ing ) frost is an important factor in se lect ion o f sowing date. A d ry , warm ripening period of o rmore is p re fe r red . Mean daily temperatures o f less than 10 to 12*^C during the growing season make wheat a hazardous crop . Knowledge o f genetic characteris tics and p a r t ic u larly the growth and development pattern o f wheat va r ie t ies is essential fo r meeting the combination o f various climatic requirements for growth development and yield formation*

The crop can uc grown on a wide range ol so i ls but medium textures are p^referred. Peaty soils containing high sodium, magnesium o r iron should be avoided. The optimum pH ranges from 6 to o. For good y ie lds the fe r t i l i z e r requirements arc up lo 150 kg/ha N , 35 to ^5 kg/ha P and 25 to 50 kg/ha K .

Wheat IS re la t ive ly tolerant to a high groundwater table; fo r sandy loom to silt loam a depth o f groundwater of 0 .6 to 0 .8 m can usually be to lera ted , and for clay 0 «8 to 1 m. For short periods the crop con withstand without v is ib le harm a minimum depth o f 0*25 m* With a r is e o f groundwater table to 0. 5 m for long periods the jneld decrease i t 20 to AO percent.

The crop is moderately tolerant to soil salinity but the ECe should not exceed A m m ho §/cm tn the upper soil le v e r dunng germination. Y ie ld decrease due to salinity IS 0% at ECe 6 .0 , 10% at 7 .A, 25% at 9*5, 50% at 13 and 100% at ECe 20 mmhos/cm.

With p r e - lm g a t io n o r sufficient ram to wet the upper soil la y e r , seeds are d r illed 2 to A cm deep as against 5 to 8 cm m dry so ils , so that light showers w ill not

cotise the «eed« to germinaia radequate f«i4iUxatlon row n imgflton «hdmcreatet to 0.25 m or mrt-f ?* ^ 0 ,15 m (4aO to TOOOO pUnt«/ha) b«fSowing rates under »rrig*t,on 200000 pUnf»/lu).c s i ) . Wheat .• often yrown " ; ! j ^ ^ 120 kg/h. (dnlied) to 110 to UO hg/Ke CVroed- as iuitable rotation crops, rotation and lequfne*, tun/lower and maiae are conaidered

WATER REQUIREMENTS

For high yields water requirements (ETm) are 450 to 650 mm depending on climate and length of growing penod. The crop coefficient (kc) rtlattng meximum evapotranspiration (ETm) to reference evapotranapiralion (ETo) tat dunng the imttal stage 0.3-0.4 (15 to 20 days), the development stage 0* 7-0.8 (25 to 30 day a), the mid-season stage 1-05-1.2 (50 to fi'’ ffl\ •* Ntc- *tac** 0 .6 * -0 ,Y /Vi to 40days)and at harvest 0 , 2 -0 . 2 5 .

WATER S r f ’ T’ p v t t 1 p

Orowt. ’. ;K’ rtOvi> , ; jml >; ' rjtig wf.cai a rc ■

*•* •• •— =— J------------- ’*Jsa L ^a s~ “

• • S i w « m * .

C ro w ih p e n o d a o f w im e r and s p n n g whaat (L a rg e , 1954)

166

G ram y ie ld and gram straw ra t io a re re la ted to the duration and in tensity o f water de fic it but the re la tions va ry depending on the growth per iod during which the d e fic its occu r. T h ere is , h o w eve r , some var ia t ion in v a r ie ty as to the magnitude of the resu lting y ie ld d e c rea se . The re la tionsh ips between re la t iv e y ie ld d e c rea se (1 - Ya/Ym ) and re la t iv e evapotranspiration d e fic it (1 - ETa/E Tm ) fo r w in t e r and spring wheat are shown m F igures 52 and 53- P o f calculation examples see p . 40 and Chapter V I .

t t - I f elO os os or 0« as ^ 03 02 0

F ig . 52 Relationship between re la t iv e y ie ld d e c rea se (1 - Ya/Ym ) and re la t iv e evapotranspiration de fic it (1 - ETa/ETm ) for w in ter wheal

.-Ql

os 07 os OS 04 03 02 Ql OS OS 07 OS OS 04 03 02 01

Fig. S3 Relationship between re la t iv e y ie ld d ec rea se (1 - Ya/Ym ) and re la t iv e evapotransp iration de fic it f l - ETa/ETm ) fo r spring wheat

The reU ttanthtpt indicaie that sensittviiy lo water deficti le ■oewwhet ht|%«r in •iprtng that in winter wheat . and thta d iffa tenc* la thought to ba tha roaah o f *coiMineiiiag*

I .11 . * 1 i i > i»,. . ,/ai 11 i . j I . . I I I , .i. ,. . i, g > «i t iM. i V , IVTt or heavy pre-and ea rly aeaaon ram can p r^ u ca good ytalda parttcuUriy

when soils a re d e ^ and have a good water holding capacity and with an adaquaie nmoitni of stored soil w ater, significant water deficits may occur only in ih e ^ e ld formaiion period 0 )> Only with irrigation o r rain in the early growth penods W and la ) pUni and head number per are considered higher compared to no ram o r irrigation . In the latter situation the lime to heading ts also usually shortened.

Slight water defic its in the vegetative penod <1) may have U ltlc effect on crop development o r may even somewhat hasten maturation. The flowenng penod (2 ) is most sensitive to w «ie r de fic it. Pollen formation and furtilication can be senously affected under heavy water stress and dunng the tune o f head development and flow enng water shortage w ill reduce the number o f heads per plant, head length and number o f grains per head. At the time of flowering root growth may be very much raducad and aigy even cease and considerable damage can be caused in this penod . The loss in yield due to water deficits during the flowering period ( 2) cirru't V.- r.* prov -water supply during the later growth periods.

Water deficit dunng the yield formation penod (3> results m reduced gram * eight and hot, dry and strong wind in combination with a water defic it dunng this period causes nhrivelling of gram. During the npening period <0 a d ry ln g *m penod IS often induced by discontinuing irrigatio- ' dunng this penod onlyhas a slight effect on yield.

In summary, provided there is adequate water during the esta' i period (0)ihc critical periods for water defi

when the plants are some i j cm ta ll, just completing tille ring and just starting elongation; at this time the total number of heads and number of potential seeds per head is l>eing dcterr

at the end o f head davclopmeni to heading o r the time that tha f lowering penod ( 2) begins ; wa'cr deficit will grestV. reduce the number of seeds per head;

at early yield formation penod (early 3) when water deficits combuied with hot, dry winds would r ■ an mconq>le*< . - i ■ * areduced y ie ld o f poorqual. d ied grains

Wheat has the ability to form additional t ille rs when hesvy water stress dunng the late vegetative penod ( I c ) is followed by heavy water application. Y ields may be improved through the formation o f additional heads but harvest ts da laye i taaaea from other causas such as lodging and non-uniform npaning are often lacreaaad.

1*7

w a t e r UPTAKE

Wheat has • prima m and la ter it develops a ftbraua root system. T1i«latu r roots are formed f r o .. lodas which a re at o r near the grouad w r fa c a . Depth and density o f rooting a re affected by w ater, nutrients end ovygmi m the ee ll* hi d e w so ils , the sctlve rooting depth fo r sprtng wheat is 0 .9 m wtth e maxtoMa o f 1.2 le 1,5 m and a spread o f 0 .15 to 0.25 m m all d irections. For wtsdar wheel, active roottag d a p *

s up to 1. 2 m wlUi aMximum of 1.5 to over 2 m and a smular spread. The top root : alto increases with crop developaieBt and is about 2 dunng the vegetative penoc

168

Q r s t n t i l l m e

Fig. 34 Critical periods for water deficit of wheat

ttbout 4 before heading, and about 10 to 11 during the yield formation (3) and ripening(4 ) period. In w in te r wheat the primary root system is developed in the autumn and full rooting depth in the spring is reached ea r l ie r than in spring wheat which requires 30 to 73 days after emergence to reach full depth.

Water uptake and extraction patterns are related to root density. In general jO to 60 percent of the total water uptake occurs from the first 0.3 m, 20 to 23 percent frotn the second 0.3 m, 10 to 15 percent from the third 0.3 m and loss than 10 percent from the fourth 0.3 m soil depth. Normally 100 percent of the water uptake occurs over the first : " ' ’ . " n (D - 1.0-1 . 3 m).

L’uUcr ^ouuuions when maximum evapotranspiration is about j to D mm/day water uptake of the crop is little affected at soil water depletion of less than 50 percent of the total available soil water (p - 0 .5 ). Moderate water stress to the crop occurs at depletion levels of 70 to 80 percent and severe stress occurs at levels e x c e^ in g 80 p e r cent.


Taking into account ETriiifcr non-stress conditions about 50 to 60 percent of available soil water con be utilized by the crop before the next irrigation, with somewhat higher depletion levels dunng the npening period (4). There is a distinct Advantage for both winter and spring wheat in having the entire root /.one filled to field capacity prior to or soon after sowing to attain optimum root development. Over- watering dunng the vegetative period (1) produces luxurious growth that can cause lodging, which may also occur after a too heavy irngation the ’ ,itp m.'M penod elate 3), particularly with sprinkler irrigation.

Where rainfall is low and irrigation water supply is limited, in addition to pre-- during the Rowenngshould be scheduled to avoid wat

1

p e n o d ( 2 ) and at about 50 t o '70 daya after aowing o f tp r tn g wheat. Irrigaitoa and rom faU d u n n g the late y ie ld formation p e n o d (late 3 ) ahow Util* effect o«i ytelde vhen sufficient aoit w a ter in the root /one , srr ie .t l^vr‘r frt'*TT' rhr p rev ir t is per iod lo «e e the c rop into the r ipen ing peno«{ ■

> »a a . U S A - W in ter Wheat lo i r r ig a te a la rg e a rea moat e f f ic ien t ly wiiii limitcil water supply: one heavy autumn ir r iga t ion to wet the full root zone du n n g S ep tem b er-N ovem b er , one apn n g i rn g a t io n and one i r r ig a t io n m the f lo w e n n g period ( 2 ).

T e z a a . U S A - W m te r Wheat

(0 high production lev e l : prop lam ing i r n gai ^ r. i o wci *oi i urol i ic lo *. , v'-.cir r iga t io n when about 120 mm o f so il wa t e r has bean depietad which with normal ra in fa l l la about M a rch , with next two ir r iga t io n s at the end o f A p n l and late M ay . When ra in fa l l is below normal du nng spring , i r r iga t ion mav be requ ired start ing o a r ly M arch .

< medium production le v e l t preplanting it t . , ; . a * i . i i . i iwhen some 1>> mm has been depleted at the beginning o f A p r i l , the aocond at tieginning o f M ay. I n d r y a r * ' '^ ' r . ' . ^nga tion * ' ’

( i l l ) low production l e v e l ; p rep lam mg i r n g a t i vm. r du n n g g* i . . at . , » iti, vticspring ir r iga t ion ea r ly May to enaura su ff ic ient so il water ava ilab le during peak w ater requirement p e r iod .

U S S R - W in ter WheatHigh y ie ld with one full i r r iga t ion and one to four apnng ir r iga t ion s with so il w a te r depletion in the f i r s t 1 m soil depth not exceed ing 70 percen t o f the total a va ilab le w ater .

gnada - W in te r Wheat One ir r iga t ion du n n g the establishment p e n o d (0 ) but st ill l>eneftctal when app lied as la ic as the n ow erm g per iod (2 ) . With two i r n g a t io n s , highest ytalda whan applied during ea r ly veg-^tativc ( l a ) and n o w e rm g p e n M s . With three ir r tga t ion a the additional application is given at the late vege ta t ive per iod ( I c ) but the a f fe c t on ylaWl between two and three sp r ing ir r iga t ion s may be smaP

Israe l (apDroKimatalv 250 gun w in ter r a n .. .m cr WhyatSowing in d ry so il with application o f ISO mm a fte r aowtng: in the case o f aubeianiial ram , ir r iga t ion ahould b r ing the upper 0 .6 m to fie ld capacity . The second ir r iga t ion la applied when w ater depletion tn tha upper 1 m has reached 100 to 120 mm. In a v e r a g e yea rs no fu n h e r i rn g a t io n la ra q u trM until heading. I f at f lo w e n n g (h e a d in g aotl water depletion is le s s than 30 aim, i rn g a t io n con be de layed until o a H y y ie ld formation p en od (e a r ly 3) when the f i r s t 0 .6 m la brought to fie ld capacity . I f at heading soil water depletion is g r e a te r than 50 nun irn g a t io n ahould be applied at that time with no further ir r iga t ion aftev'wards.

la rae l - S p r in e WheatDunng ea r ly growth adequate w ater ahould be ava ilab le tn the aotl p r o f i l e end one application o f ISO mm is recommended. W in te r re in a of 250 mm a re usual W adequate to bn n g the crop to maturity. At f lo w e n n g ISO mm o f ava ilab le aotl w a ter ahould be stored m the root zonct when sm a lle r , an additional i rn g a t io n la requ ired .

Northern India . Swriua WheatIn addition to p r e - im g o t i o i i , one irrigation du n n g e e r lv vegeta t ive penod (la), imgationa - one dunng early vege io t tv e penod (fe) and one |uat pner to heed emergencethrough n ^ 'w rrin c ih r e r t m e e tto n s - d u r in g r s r l v ve g e ta tiv e p e n o d ( l a ) , fuat

prior to hesd developmeni through riowering period (2 ) and early yield formation period (early J): four irrigations - dunng early vegetative ( l a ) , late vegerativo ' flcwermc(2 ) and early yield formation (ea r ly 3) penods.

170

IRRIGATION MFTHCDS

Normal!^ . - . I : . ' ' U C I j .v l ' mcihotl> >.'i U i i T o w , i v i ' v i o r . . t iu l

basin are most common. Sprinkler trnga iion is also practised, especia lly when water supply 19 limited or the topography o r the soil are less suited to surface irr igation ,

YIELD AND Q U ALITY

When yields are low under limited water supply, the protein percentage of the gram in creases , particularly under high nitrogen application. The effect o f nitrogen on protein percentage is much reduced under medium to optimum water supply, although both grain and protein yield arc higher. Water defic its during the yield formation penod result in shnvellcd grains which reduce flour y ie ld .

A good yield of wheat under irrigation is 4 to 6 ton/ha (1 2 to 15 percent moisture). The water utilization effic iency for harvested yield (E y ) for gram is about 0 .8 to 1.0 kg/m*.

U IS a s s u m e d t h a t w h e n O n + P e + W b ) < ( 3 0 . E T m ) o n a m o n th ly b a s is , th e n e t i r r i g a t i o n a p p l i c a t io n ( I n ) a n d th e e f f e c t i v e r a i n f a l l ( P e ) w i l l f u l l y c o n t r ib u t e to e v a p o t r a n s p i r a t io n a n d n o d e e p p e r c o la t io n a n d r u n o f f w i l l o c c u r . A l s o , m e a n m o n th ly E T a IS n o t a f f e c te d b y th e d i s t r i b u t i o n o f In a n d P e o v e r th e m o n th ( T a b le 2 2 , P a r t A . 111).

172

A P P E N D I X I I

G L O S S A R Y

A i r r i g a t e d

A a i r r i g a t e dm e t - h a

A m i r r i g a t e d

A S l a v a i la b lew a t e r s u p p ly f r o m i r r i g a t i o n , r a i n a n d s t o r e d s o i l w a t e r i s a d e q u a te to m e e t f u l l c r o p w a t e r r e q u i r e m e n t s ( E T m ) - f r a c t i o n

c a d ju s tm e n t f a c t o r f o r c a lc u la t e d r e f e r e n c e e v a p o t r a n s p i r a t io n ( E T o ) in th eP e n m a n a n d R a d ia t io n m e th o d s - f r a c t i o n

c H c o r r e c t i o n f o r h a r v e s t e d p a r t o n n e t t o t a l d r y m a t t e r o f a c r o p , a ls o c a l le dh a r v e s t in d e x - f r a c t i o n

c L c o r r e c t io n f o r c r o p d e v e lo p m e n t o v e r t im e a n d le a f a r e a o n t o t a l d r y m a t t e ro f a c r o p - f r a c t i o n

c N c o r r e c t i o n f o r n e t d r y m a t t e r ( r e s p i r a t i o n ) o n g r o s s d r y m a t t e r o f a c r o p -f r a c t i o n

c T c o r r e c t i o n f o r te m p e r a t u r e o n g r o s s d r y m a t t e r ( p h o t o s y n t h e s is ) o f a c r o p -f r a c t i o n

D r o o t d e p th o r s o i l d e p th f r o m w h ic h th e c r o p e x t r a c t s m o s t o f t h e s o i l w a t e rn e e d e d f o r e v a p o t r a n s p i r a t io n o r e f f e c t i v e r o o t d e p th - m

d n e t d e p th o f i r r i g a t i o n w a t e r a p p l i c a t i o n - m m

E a f i e ld a p p l i c a t io n e f f i c i e n c y o r r a t i o b e tw e e n th e a m o u n t o f w a t e r s t o r e d in th er o o t z o n e a n d th e a m o u n t o f w a t e r s u p p l ie d a t t h e f i e ld i n l e t - f r a c t i o n

e a s a t u r a t io n v a p o u r p r e s s u r e o r u p p e r l i m i t o f p r e s s u r e e x e r t e d b y w a t e r v a p o u rin th e a i r w h e n s a tu r a te d a t a g iv e n a i r t e m p e r a t u r e - m b a r

E b f i e ld c a n a l e f f i c i e n c y o r r a t i o b e tw e e n th e a m o u n t o f w a t e r s u p p l ie d to th e f i e ldin le t a n d th e a m o u n t o f w a t e r s u p p l ie d t o a b lo c k o f f i e ld s - f r a c t i o n

E c c o n v e y a n c e e f f i c i e n c y o r r a t i o b e tw e e n th e a m o u n t o f w a t e r s u p p l ie d to a b lo c ko f f i e ld s a n d th e a m o u n t o f w a t e r d i v e r t e d a t h e a d w o r k s - f r a c t i o n

E C e e l e c t r i c a l c o n d u c t i v i t y o r m e a s u r e o f s a l t c o n t e n t i n th e e x t r a c t e d s o i l w a t e rw h e n th e s o i l i s s a tu r a te d w i t h w a t e r - m m h o s /c m

e d a c tu a l v a p o u r p r e s s u r e e x e r t e d b y w a t e r v a p o u r c o n ta in e d in th e a i r - m b a r

E m w a t e r u t i l i z a t i o n e f f i c i e n c y f o r t o t a l d r y m a t t e r p r o d u c e d b y th e c r o p p e r u n i to f w a t e r e v a p o t r a n s p i r e d - k g /m ^

E p p r o j e c t e f f i c i e n c y o f r a t i o b e tw e e n th e a m o u n t o f w a t e r s t o r e d in th e r o o t z o n ea n d th e a m o u n t o f w a t e r r e le a s e d a t p r o j e c t h e a d w o r k s (E p = E a , E b . E c ) - f r a c t i o n

E p a n p a n e v a p o r a t io n o r r a t e o f w a t e r lo s s f r o m a n u n s c r e e n e d c la s s A p a n - m m /d a y

E T a a c t u a l c r o p e v a p o t r a n s p i r a t io n r a t e ( E T a < E T m ) - m m /d a y o r m m / p e r io d

E T m m a x im u m e v a p o t r a n s p i r a t io n r a t e o f th e c r o p w h e n s o i l w a t e r i s n o t l i m i t e d ;a ls o c a l le d c r o p w a t e r r e q u i r e m e n t s - m m /d a y o r n u n / p e r io d

174

E T o r e f e r e n c e e v a p o t r a n s p i r a t io n r a t e f o r a g iv e n c l im a t e w h e n s o i l w a t e r i s n o tl im i t e d - m m /d a y o r m m / p e r io d

E y w a t e r u t i l i z a t i o n e f f i c i e n c y f o r h a r v e s t e d y ie l d o r th e a m o u n t o f h a r v e s t e dy i e l d p r o d u c e d b y th e c r o p p e r u n i t o f w a t e r e v a p o t r a n s p i r e d ( h a r v e s t e d p a r t in c lu d e s m o is t u r e p e r c e n t a g e s p e c i f ic to th e c r o p p r o d u c t ) - k g /m ^

F f r a c t i o n o f th e d a y t im e th e s k y i s c lo u d e d - f r a c t i o n

f ( ) f u n c t io n o f ( )

G le n g t h o f t o t a l g r o w in g p e r i o d o f a c r o p - d a y s

G e e f f e c t i v e c o n t r ib u t io n o f g r o u n d w a t e r t o e v a p o t r a n s p i r a t io n - m m / p e r io d

i i r r i g a t i o n i n t e r v a l b e tw e e n s u c c e s s iv e i r r i g a t i o n a p p l i c a t io n s - d a y s

I n n e t i r r i g a t i o n r e q u i r e m e n t s o r sum o f c r o p w a t e r r e q u i r e m e n t s ( E T m ) m in u se f f e c t i v e r a i n f a l l ( P e ) , g r o u n d w a t e r c o n t r ib u t io n (G e ) a n d s t o r e d s o i l w a t e r ( W b ) ; ( I n = E T m - P e - G e - W b ) - m m / p e r io d

K c o r r e c t io n f o r c r o p s p e c ie s o n g r o s s d r y m a t t e r o f a s ta n d a r d c r o p - f r a c t i o n

k c c r o p c o e f f i c i e n t r e l a t i n g r e f e r e n c e e v a p o t r a n s p i r a t io n r a t e ( E T o ) to th em a x im u m e v a p o t r a n s p i r a t io n r a t e ( E T m ) , o r E T m = k c , E T o - f r a c t i o n

k p a n p a n c o e f f i c ie n t r e l a t i n g th e p a n e v a p o r a t io n r a t e ( E p a n ) to th e r e f e r e n c e e v a p o t r a n s p i r a t i o n r a t e ( E T o ) , o r E T o = k p a n . E p a n - f r a c t i o n

k y 3/T.eld r e s p o n s e f a c t o r o r r a t i o b e tw e e n r e l a t i v e y i e l d d e c r e a s e (1 - Y a / Y m ) a ndr e l a t i v e e v a p o t r a n s p i r a t io n d e f i c i t (1 - E T a / E T m ) f o r h ig h p r o d u c in g v a r i e t i e s a d a p te d t o th e g r o w in g e n v ir o n m e n t - f r a c t i o n

L A I l e a f a r e a in d e x o f a c r o p o r r a t i o b e tw e e n th e g r e e n l e a f a r e a a n d th e g r o u n ds u r f a c e - m ^ /m ^

L R le a c h in g r e q u i r e m e n t o r th e d e p th o f w a t e r r e q u i r e d t o d r a i n th r o u g h th e r o o tz o n e to c o n t r o l s o i l s a l i n i t y i n r e l a t i o n to n e t i r r i g a t i o n r e q u i r e m e n t s ( I n ) - f r a c t i o n

N m a x im u m p o s s ib le s u n s h in e d u r a t io n - h o u r / d a y

n a c t u a l s u n s h in e d u r a t io n - h o u r / d a y

P t o t a l p r o d u c t io n o f a c ro jp p e r u n i t a r e a ( Y a ) f o r th e p r o j e c t a r e a ( A ) ;(P = Y a . A ) - k g o r to n / s e a s o n

p p o r t i o n o f t h e t o t a l a v a i la b le s o i l w a t e r w h ic h c a n b e d e p le te d w i t h o u t a f f e c t in gm a x im u m e v a p o t r a n s p i r a t io n r a t e ; ( E T a = E T m ) - f r a c t i o n

P a t o t a l c r o p p r o d u c t io n f r o m a c r e a g e A a , p a r t i a l l y m e e t in g c r o p w a t e r r e q u i r e m e n ts ; ( E T a < E T m , Y a < Y m ) a n d ( P a * A a . Y a ) . - k g o r to n / s e a s o n

P e e f f e c t i v e r a i n f a l l o r th e p a r t o f th e p r e c i p i t a t i o n t h a t c o n t r ib u t e s to c r o p w a t e rr e q u i r e m e n t s - m m / p e r io d

P m t o t a l c r o p p r o d u c t io n f r o m a c r e a g e A m , m e e t in g f u l l c r o p w a t e r r e q u i r e m e n t s ;( E T a = E T m , Y a = Y m ) a n d (P m = A m . Y m ) - k g o r t o n / s e a s o n

R a e x t r a t e r r e s t r i a l r a d i a t i o n r e c e iv e d a t th e to p o f th e a tm o s p h e r e - c a l / c m ^ / d a yo r m m e q u iv a le n t e v a p o r a t io n / d a y

R H r e l a t i v e h u m id i t y o r a c tu a l a m o u n t o f w a t e r v a p o u r ( e d ) a t a g iv e n te m p e r a t u r ein r e l a t i o n to th e m a x im u m a m o u n t th e a i r c a n h o ld a t t h a t t e m p e r a t u r e ( e a ) - p e r c e n t

R H m a x m a x im u m r e l a t i v e h u m id i t y d u r i n g a d a y o r m e a n o f d a i l y m a x im a f o r a p e r io d -p e r c e n t

R H m e a n m e a n r e l a t i v e h u m id i t y d u r i n g a d a y o r f o r a p e r i o d - p e r c e n t

175

R n t o t a l n e t r a d i a t i o n o r th e d i f f e r e n c e b e tw e e n in c o m in g a n d o u tg o in g s h o r t w a v ea n d lo n g w a v e r a d i a t i o n - c a l / c m 2 / d a y o r m m e q u iv a le n t e v a p o r a t io n / d a y

R n l n e t lo n g w a v e r a d i a t i o n o r d i f f e r e n c e b e tw e e n o u tg o in g a n d in c o m in g lo n g w a v er a d ia t i o n - c a l / c m 2 / d a y o r m m e q u iv a le n t e v a p o r a t io n / d a y

R s In c o m in g s h o r t w a v e r a d i a t i o n - c a l / c m 2 / d a y o r m m e q u iv a le n t e v a p o r a t io n / d a y

R s e m a x im u m a c t i v e in c o m in g s h o r t w a v e r a d i a t i o n o n c l e a r d a y s o r th a t p a r t o f th em a x im u m in c o m in g s h o r t w a v e r a d i a t i o n o n c le a r d a y s th a t is e f f e c t i v e in p h o t o s y n th e s is - c a l / c m 2 / d a y

S a t o t a l a v a i la b le s o i l w a t e r w h ic h is b e tw e e n f i e ld c a p a c i t y ( 5 f c ) a n d w i l t i n gp o in t ( S w ) - m m /m

S fc s o i l w a t e r c o n te n t a t f i e ld c a p a c i t y o r d e p th o f s o i l w a t e r h e ld in th e s o i l a f t e ra m p le i r r i g a t i o n o r h e a v y r a i n w h e n , a f t e r 1 to 3 d a y s , th e r a t e o f d o w n w a r d m o v e m e n t h a s s u b s t a n t ia l l y d e c r e a s e d o r w h e n s o i l w a t e r te n s io n is 0 . 1 lo 0 , 3 a tm o s p h e r e - m m /m

S t a c tu a l d e p th o f a v a i la b le s o i l w a t e r a t a g iv e n p o in t in t im e - m m /m

S w s o i l w a t e r c o n te n t a t w i l t i n g p o in t o r d e p th o f s o i l w a t e r h e ld in th e s o i l a t s o i lw a t e r te n s io n o f 15 a tm o s p h e r e w h e n p la n t s a r e c o n s id e r e d f o r p r a c t i c a l p u r p o s e s t o be n o lo n g e r a b le t o e x t r a c t w a t e r f r o m t h e s o i l - m m /m

T t e m p e r a t u r e o f t h e a i r -

t n u m b e r o f d a y s a f t e r i r r i g a t i o n - d a y s

t ' n u m b e r o f d a y s a f t e r i r r i g a t i o n d u r in g w h ic h E T a = E T m - d a y s

T m e a n m e a n d a i l y t e m p e r a t u r e o f th e a i r - ° C

U t o t a l w in d r u n a t 2 m h e ig h t - k m / d a y

U d a y t o t a l w in d r u n o r a v e r a g e w in d s p e e d d u r i n g d a y t im e a t 2 m h e ig h t - k m / d a y o rm / sec

U m e a n m e a n t o t a l d a i l y w in d r u n o r a v e r a g e d a i l y w in d s p e e d a t 2 m h e ig h t - k m / d a y o r mf s e c

U ru g h t t o t a l w in d r u n o r a v e r a g e w in d s p e e d d u r i n g n ig h t a t 2 m h e ig h t - k m / d a y o rm /s e c

V i r r i g a t i o n s u p p ly r e q u i r e m e n t s o r th e t o t a l v o lu m e o f w a t e r d e l i v e r e d o v e ra g iv e n p e r i o d to a f i e l d , a b lo c k o f f i e ld s o r p r o j e c t a r e a - m V p o r io d

W w e ig h t in g f a c t o r in th e P e n m a n a n d R a d ia t io n m e th o d s , d e p e n d e n t o n te m p e r a t u r e a n d a l t i t u d e - f r a c t i o n

W b a c tu a l d e p th o f a v a i la b le s o i l w a t e r o v e r th e r o o t d e p th a t t h e b e g in n in g o f ap e r io d - mm

W e a c tu a l d e p th o f a v a i la b le s o i l w a t e r o v e r th e r o o t d e p th a t th e e n d o f a p e r io d -mm

Y a a c tu a l h a r v e s t e d y i e l d o f a h ig h p r o d u c in g v a r i e t y , a d a p te d t o th e g iv e ne n v ir o n m e n t w i t h g r o w t h f a c t o r s o t h e r th a n w a t e r n o t l i m i t e d (Y a < Y m ,ETa< ETm) - kg or ton/ha

y c g r o s s d r y m a t t e r p r o d u c t io n r a t e o f a s ta n d a r d c r o p f o r a g iv e n lo c a t io n o n ac le a r ( c lo u d le s s ) d a y - k g / h a / d a y

Ydm maximum net total dry matter of a crop - kg or ton/haY m m a x im u m h a r v e s t e d y ie l d f o r a h ig h p r o d u c in g v a r i e t y a d a p te d to th e g iv e n

e n v ir o n m e n t w i t h g r o w t h f a c t o r s n o t l i m i t e d - k g o r t o n / h a

y m m a x im u m l e a f g r o s s d r y m a t t e r p r o d u c t io n r a t e o f a c r o p f o r a g iv e n c l im a t e -k g / h a / h o u r

V m e c a lc u l a t e d m a x im u m h a r v e s t e d j r ie ld in d r y w e ig h t f o r a h ig h y ie l d in g v a r i e t ya d a p te d t o th e g iv e n e n v ir o n m e n t w i t h g r o w t h f a c t o r s n o t l im i t e d (m e th o dc a l i b r a t e d w i th e x p e r im e n t a l r e s u l t s ) - k g / h a o r t o n / h a

Y m p c a lc u la t e d m a x im u m y ie ld p o t e n t ia l in d r y w e ig h t f o r a h ig h p r o d u c in g v a r i e t ya d a p te d t o th e g iv e n e n v ir o n m e n t w i t h g r o w t h f a c t o r s n o t l im i t e d - k g / h a o rt o n / h a

Y o g r o s s d r y m a t t e r p r o d u c t io n r a t e o f a s ta n d a r d c r o p f o r a g iv e n lo c a t io n -k g / h a / d a y

y o g r o s s d r y m a t t e r p r o d u c t io n r a t e o f a s ta n d a r d c r o p f o r a g iv e n lo c a t io n o n ac o m p le te ly o v e r c a s t ( c lo u d e d ) d a y - k g / h a / d a y

176

PERSONS AND INSTITUTES CONSULTED

Appreciation is expressed and acknowledgement is paid to the following people for advice given and information provided:

AustraliaKnight R , , Acting Head-Department o f Agronomy, Waite Agricultural Research Institute, The Univ

ersity of Adelaide, Glen Osmond, South Australia 50t^Nix H ,A , , Department of Land Use, CSIRO, P .O . Box IbOO, Canberra City ACT Puckridge D .W . , Waite Agricultural Research Institute, The University of Adelaide, Glen Osmond,

South Australia 5064Snaydon (D r . ) , Division of Plant Industry, CSIRO, P .O . Box 1600, Canberra City ACT

BrazilReichardt K . , CENA, C .P . 96, 13400 Piracicaba SP

Canada

Tn vett N . B . A . , P ro fessor , Department of Geography, College oi Social Science, University of Guelph, Guelph, Ontario N l6 2W1

Cyprus

Krentos V . D . , Head, Soils and Water Use, Ministry of Agriculture and Natural Resources, A g r i cultural Research Station, Nicosia

DenmarkJensen S . , Royal Veterinary and Agricultural College, The Climate and Water Balance Station,

2630 Taastrup, Bojbakkegard

Ethiopia

Retta A . , Melka Werer Research Station, P .O . Box 2003, Addis Ababa

FranceDamagnez J ., Centre de Recherches Agronomiques du Sud-Est, Station de Bioclimaiologic, Cantarel

84, Montfavet

Germany. Federal Republic of

Hanus H . , Professor, Christian-Albrechts Univers ity , K ie lVon Hoyningen-Huene Leichiweiss Institut fiir Wasserbau, Technlschen UniversitSt, Braunschweig

Hungary

Balogh J,, Hungarian National Committee IC ID , Budapest V , Miinnich Ferenc u. 7 CseliStei L . , Universitas Scietiarum Agriculturae, Institucian Horticulturae, GiSd«Mli>Petrasoviis (D r . ) , Ministry of Water Resources, Budapest

India

Hukkeri S . B , , Division of Agronomy, Indian Agricultural Research Institute, New Delhi 110012 Sharma H .C . , Haryana Agricultural University, Hissar 125004

IsraelBielorat H. ,• Institute o f Soils and Water, Division o f Environmental Physiology and Irrigation,

Agricultural Research Organization, The Volcani Center, P .O .B , 5, Bet Dagan 50200 Blum A . , Institute of Field and Garden Crops, Agricultural Research Organization, The Volcani

Center, P .O .B . 6, Bet Dagan 50200 Gil N . , 23 Haoranim Street, Kfar ShmariahvLomas J., Director, Division of Agricultural Meteorology, Ministry of Transport, P .O . Box 25,

Bet Dagan

APPENDIX III

Sranhill G. , Agricultural Research Organization, The Volcani Center, P .O .B . 6, Bet Dagan 50200 Yaron B ., Department of Agricultural Economics, The Hebrew Univers ity , Rehovct

UalXAboukaled A . , International Centre for Advanced Mediterranean Agronomic Studies, Institut de B an ,

5tr , P ro v . CegUe, Valcnzano Caliandro A , , Institut de Bari, Str* P ro v , Ceghe, ValenzanoCo Cascio B . , Instiiuto di Agronomia Generale e Coltivazione Erbacee, Univ. dfegli Studi di Palermo,

Viale delle Scienze, 90128 Palermo Ravelh F . , Cassa per il M ezzog iom o, Via Giorgione 2a, Rome

Lebanon

Sarraf S , , Institut de Recherches Agronomiques, Te l Amara

Netherlands

Rjcrhuizen ] . F , , Afd. Tuinbouw plantenteelt. Agricultural University, Wageningen Feddcs R . A . , Institute for Water Management, Prinses Marijkeweg, Wageningen Rijtema P . E . , Institute for Water Management, Prinses Marijkeweg, Wageningen Slabbers P . ) . , International Institute for Land Reclamation and Improvement, P . O . Box 2-5,

WageningenSorbello Herrendorf V . , International Institute for Land Reclamation and Improvement, P .O . Box

25, WageningenVan Heomst F l.D ,]. , Centrum Agro Biologisch Onderzoek (CABO), Wageningen Van Keulcn H ., c/o Afdeling Theoretische Teeltkunde, Landbouw hogeschool, Salverdaplein 10,

WageningenVink N . H . , Department of Irrigation and Civil Engineering, Agricultural Univers ity , Nleuwe Kanaal

11, Wageningen

P a k i s t a n

Chaudri Nur M . , Punjab Agricultural Research Institute, FaisalabadNasri S . N , , Irrigation. Drainage and Flood Control Research Council, Waterlogging and Salinity

Study C e l l , 106-C/2 Gulberg III, Lahore

Sudan

FI Nadi A .H . , Department of Agronomy, Faculty of Agriculture, Sham bat F'arbrother H. , Gezira Research Station, P .O . Box 338, Wad Mcdani

Syrian Arab Republic

Matar A . , Head, Soil Department, Faculty of Agriculture, University of T ichreen, Lattakia

United Kingdom

Clarke R . T . , Institute of Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxon. C u r r i e ] , A , , Rothamsted Experimental Station, Harpenden, Herts. A L5 2JQ Dent D .L . , School of Environmental Sciences, University of East Atiglia, Norwich NR2 7TJ Hey R.D. , School of Environmental Sciences, University of East Anglia, Norwich NR2 7TJ Jones H.G. , Department of Botany, The University, Glasgow G12 8QQ

USA

A r k in G .F . , U SD A-A RS , Bushland, TexasBaker C .V . , Programming Supervisor, Colorado State University, College of Natural Sciences,

Natural Resources Ecology Laboratory, Fort Collins, Colorado 80523 Curry R . B , , Ohio Agricultural Research Development Center, Wooster, Ohio 42691 Danielson R .E . , Department of Agronomy, Colorado State University, Fort Collins, Colorado 30523 Dethier B .E . , Department of Atmospheric Sciences, Cornell University, Ithaca Gibson J .H ,, D irector, College o f Natural Sciences, Natural Resources Ecology Laboratory,

Colorado State University, Fort Collins, Colorado 80523 Goodridge ] .D , , Climatologist, Water Resources Evaluation, Division o f Resources Development,

P .O . Box 388, Sacramento, California 95002 Gorbei D . W . , Agricultural Research Center, Route 3, Box 383, Marianna, Florida 32226 Hnise H .R . , Water Management Investigations, U SD A-A R S , P .O . Box E, Fort Collins, Colorado

30521Hanks R , ] . , Utah State University, Losan. Utah 82322

178

3 9 0 )

179

Henderson D .W ., Water Science and Engineering, iJniversity of California, Davis, California 95616 Hiler E .A . , Department o f Agricultural Engineering, Texas A&M Univers ity , Lubbock, Texas HiH R .W . , Department of Agricultural and Irrigation Engineering, College of Engineering, Utah

State University, Logan, Utah 8^322 Houston C .E . , 1012 M il le r D r ive , Davis, California 95616Howell T . A . , Department of Agricultural Engineering, Texas A&M Univers ity , College Station,

Texas 778^3James D .W . , Department of Soil Science and Biometeorology, Utah State Univers ity , College of

Agriculture, Logan, Utah 8A322 Jensen M . F.. , Snake R iver Conservation, U SDA-ARS , Route 1, Box l86, K im berley , Idaho 8332.1 Johnson W .C . , U SD A-ARS , Bushland, Texas K e l le r , Utah State University, Logan, Utah 82322Kruse E .G . , A R S , Engineering Research Center, Colorado State Univers ity , Foothills Campus,

Fort Collins, Colorado 80521 Lambert J .R . , Department of Agricultural Engineering, College of Agricultural Sciences, Clemson

University, Clemson, South Carolina 29631 LeM ert R. , Imperial Valley Conservation Research Center, 2151 Highway 86, Brawley, California

92227Lew is R .B , , Agricultural Engineering and Technology Department, Texas Technical University,

Lubbock, Texas 79209McGill ivray N . A . , Water Utilization Section, San Joaquin District, Department o f Water Resources,

3372 E, Shields Avenue, Fresno, California 93725 Musick ] . T . , U SD A -AR S , Southwestern Great Plains Research Center, Bushland, Texas 79012 Pruitt W .O . , University of California, Davis, California 95616 Ritchie J .T . , U SD A-A RS , Bushland, TexasRosenberg N .J . , University of Nebraska, College of Agriculture and Home Economics, The A g r i

cultural Experiment Station, Nebraska Skogcrboe G . V , , O ff ice of International Programs, Cususwash Water Management Research P ro je c t ,

Colorado State University, Fort Collins, Colorado 80521 Splinter W .E . , College of Engineering and Architecture, College of Agricu lture, University of

Nebraska, Lincoln, Nebraska 68503 S ta p p e rM . , U SD A-ARS , Bushland, TexasStewart J . I . , University o f California, Davis, California 956X6Tovey R . , Agricultural Experiment Station, University o f Nevada, Reno, NevadaWendt C .W , , Department of Agricultural Engineering, Texas A&M Univers ity , Lubbock, TexasWierenga P . ] . , College of Agriculture and Home Economics, Department of Agronomy, Box 3Q,

Las Cruces, New Mexico 88003 W i lU s W .O . , U SD A-A R S , Fort Collins, Colorado

Zambia

AeppU H . , National Research Station, Mazabuka De MilUano W . , National Research Station, Mazabuka Tliorpe T . K . , National Research Station, Mazabuka

FAO

Headquarters: H rabovszky ], (AGD); Arens P . , Braun H ,, Higgins G . , Kowal ] . , Sagardoy J. A . , Westcot D,W, , Van Velthuizen H, (A G L ) ; A l- ]ibouri H , , Bennett E . , Chiarappa L . , Dries sen } . , Gonzales, Menini U . G . , Poulton C . , Risopoulos S , , Riveros F *, Ruck H . (A G P )

Regionai Office for the Near East: A , A ra rRegional Office for Asia and Far East; K .S , ParkRegional Office for I.atin America: K, TakamiyaPro jec t : T F .L IB 9197 - L . T . ChinPro ject: NIR 69/027 - K . MacleanPro iec t : BRA 72/008 - A ,A , M il la rPro ject ; UAE 73/008 - C .R .K . Prashar, A ,P . Sa w a

ON

Neghassi H .M , Water Resources Branch , Center for Natural Resources , Energy and Transport, Headquarters, New York , NY 10017, USA

WMO

Maunder W,J, Chief, Agricultural Branch, WMO, Case Postale No, 1, CH-1211 GENEVA 20, Switzerland

I l iU ' r 1. . A , , H o w e l l t . A , . l . o w i s k . B . nnil P . 1 ' . I n iR'^i ioi i t i in tns bjf the M r c i « d a y i n d c *10 ' . , I r a i . s . A S A ! ; 1 7( L ) ; l O I

( h i l e i h . , P a w i i / i i . , ! e rk e lt aL i l j R , , L i p e rm a i i (.h , M o r R o l i u M ■ , Si I b e r b u s c h M , and B a r Y ,l t i n i i e r i L . c o f ( l i f f o r e n l i r n g i i t i o n a n d f e n i l i / a i u m r e g i m e s o n i ( i o f i e l d w a t e r b a l a n c e a n dw a t e r u . e e f l i i i e i u i . H e b r e w h n i v e n s t v o f l e r u s n i e m , I - a c u i t y o f A g r i c u l t u r e , D e p o r t i i i e t i l o f S o i l a n d W a t e r S c i e n c e . d ‘ i p .

I f o w c l l I and H i t e r E , A , Llp ti tn i7o tion o f w a t e r i i a e e f f j c i e n c y u n d e r h igh f r e q u e n c y i r r t g o t i o n -I d r ) L. I v a p o t r a n s p i r a t i o n and y i e l d r e l a t i o n s h i p ; | | . S y s t e m s i m u l a t i o n and d v n a m ie p r o

g ra m m in g . I r a n ? . A S A f ; . p .

It n o r T . L’ . 'tnd A c e v e d o t . p l a n t r e s p o n s e to w a t e r d e l i e i t s , wa t e r u s e e f f i c i e n c y and d r o u g h t l y M r e s i s t a n c e . A g r i c . f A c t e o r o l . l i : j i ) - 8 £ l .

H s i a o 1 . 1 l - e r e r e s E . , A c e v e d o P . a n d H e n d e r s o n D , W , W a t e r s t r e s s a n d d y n a m i c s o f g r o w t hI H A a n d y i e l d o l c r o p p l a n t s . I n ; W a t e r a n d P l a n t 1 i f e . P r o b l e m s a n d M o d e r n A p p r o a c h e s .

e tls , i . s n g e 0 . 1 , , K a p p en 1 . and S . h u l / e T, . I ) . h c o l o g i c a ! S iu ch es V o l . 19. S p r i n g e r V c r l a g , i ' e r l i i i . p .

II i gh es l l . D . ,ifid M e t c a l f s ’ D . f - . C > o p 1'r o d u c t l O i i . . Ird e t i l t i o i i . M a c M i i l f l n , N e w Y o r k a n d IH/J c o l l i e r - M a c M i l la n , L o n d o n . b7^ n .

l a i n I . t , a n d M i s r a I > . K , p f l e c t o f w a t e r s t r e s s o n ; 1 . P h y s i o k i g i c a l a c n v i t i e s Of p l a n t s , Ind ia nIH/H 1. A g r o i i . l n ; 3 b - i h .

ie i i se: , M , f - . S c h e d t i l i r g i r r i g a t i o n w i th c o m p t t t e r s . j . .bviil W a t e r C o n s e r v a t i o n I 9 J - 19''^.1 yfel

h as sam A . H , N e t Inotnass p ro d i i c t i e n and y i e l d ol c r o p s . P r e s e n t and r o t e n t i a l Land U s e by A g r o -iS/*; c c o L ' g u a l / o n e s p r o j e c i , l A O , R o m e ,

L n .s .n n A . H . t ' r o p s o f the W e s t A f r i c o r . ‘^ e t n i - a r i d T r o p i c s . In to rn fl l i onr tI C r o p s R e s e a r c h Ins ti 19 7(1 I t i le t o r th e Y c m i - a r i d i t o p i c s , 1 -11 /Vh l i e g u m p e t , H y de r n l i a d 'Ak ’ U l b , A , P , , In d ia .

Kos ..am A . n , and K o w a l l . M . t r o p p r o d u c t i v i t y m S a va n n a and R m n T orc .st to ne ' s in N i g e r i a , l y . ' d S a v a n n a ,

S ip j i s M . h . f ' r o d u c t i o n o f l i e l d C r o p s . A T e x t b o o k o f A g r o i i o m v , M cC .r sw - H 111 , N e w Y o r k . 791' p .

id'ItKnott J . f , t l . 'indbook l o r V e g e t a b l o G r o w o r . s . W i l e y , N e w Y o r k , i l i f i p . ( r e v i s e d ) l « t- . '

K o w n t J, R . it l ia i io i i .tin! p o l o n t i a ) . r o p p r o d u c t i o n at .Samaru , N i g e r i a , Sa vn ju io 1C 1) : 8 9 - U ) ) .1 0 ' :

K .'W.it I . and A d e o c e K . An as .sessm on i o l a r i d i t y and Hio v t ' v c r i l v o f i l ie d r o u g h t in N o r t b e n i I d . ' t N i g c i in a n d n e m l i t o u r i i i g c o u n t r i e s . S a v u u n t i d i L ) ; I C. 1 " g l .

Kow . i l i k f ’ . M n l l i e m a i K o l meulol o f w a t e r m a n a g e m e m m plan t p r o d u c t i o n . Insti iu i i t v o o r C u l i u u r . l y i t c . h n ik on W a tc r l i t i i s ho ud i i i g , W a g e n i n g e n . l i p .

I . inoc tt 1 . , K o p p e n ) . and s . Su l/o L . i ) . ( o d a ' . W a t e r and IH >itii 1 i f e . P r o b l e m s and M cs le rn i ( l ' ( 7 A p p t o a c l i e s . h c o l o g i c a l s i m l i e s N o . 19. S p r i n g e r V c r l a g , H e r t i n , l l e i d e l b e r g . N e w

Y o r k , s it - t i .

M o n ie iH i ! . l . r t i i u - p l c s o f l . nv , i on m en la I r i i v s i t s . 1 d w u r d A r n o l d , L o n d o n , i i 1 p .I97 ' i

M o n le i t h 1.1 . S o l a r r a d i a t i o n and p r o d u i i ivt t v ni i r o p i c n i e o o s v s t e m s . P n p s c o t ' o n f e r c n c e ;■,‘ iTti P t O i U i c t I v i l v 01 1 r o p i c u i h i o s vs tcn i s , P gan-la , S c p tem l> er .

M c im e ii l . 1.1 . h v a p o r a t i o n and e n v i r o n m r n t , P r o c . Sv tnp. S o c . F x p , R i o t , 1 9 : L'ti j - i t 7 . ,I9lt>

N cg l in s J i H . M . 1 r o p w n i e r u se and v i e l d m o d e l * w i th l i m i t ed s o i l w n t e r . P ( iD I h e . s i s . W a t e r I ' t ' . ; M a n a g e m en t T e c h . R e p . N o . ^ 2 , t 'ct lc irndo S t a t e H n t v e r s t t y , ! e r f ( o l l i n s , ( .OlOrnrlO.

Nci l- I K . t . and C’ f o i g ) . K , An a g r e e Itmat i c p f o c o d i i r e to d e t e r m i n e g r o w i n g s e a s o n l o r v e g e t a b l e s .I ' 1 ' i ; i 9 7 , ' A g r i . . M e ts 'o r , ' l . <^ :dL ' ' , -7d i ' .

I ’ O M n t n g J e V r i o s I ' . W . r , S i m i i l o t i o n d e r A s s i m i l a t i o n u i i d 1 r a n s p i r a t i o n d o r I ’ D a n i e n i l e c k e n a c h I 9 ' i r .r u t id lc g e i i d c t i ( ' reset/ rt t . I ' e i l r a g riiin pym pOsiun' ' Hi oph y s i l p I un r 1 ic be r S y s t e m r ’ .

P o t s d a m , I o - 1 7 O c t o b t r .

P e n r u r i a d e V n e s F , W . T . A m o d e l f o r y t m u l a l i n g t r a n s p i r a t i o i i o f l e a v e s w i t h s p e c i a l a l t e m i " . b1 9 7 2 s t o m a t t t l f u n c t i o n f n g , ] . A p p l i e d P c o l o g y 9 13 7 - 7 7 .

P r a s h a r C . R . K . , P e a r l R . a r v l H a g a n R , M . R e v i e w o n w a t e r a n d c r o p q u a 1 1t v ■ S c i g i i t t a 1 9 7 6 H o r t i c u L t u r a e 5 : l M - 2 0 3 .

P u r a e g l o v e J . W . T r o p i c a l C r o p s . D i . o t y l e d o r i s 1 a n d 7 . l . o i i g m a i i s ,

R i j t e m a P . P . P r o d u k t i e e n v e r d a m p i n g i n d o m o d c r n e b c - d e t n k u n d o . N o l - i 79 " , . i r W , W . i c c i m g e n . 1 9 7 i F e b r u a r y .

R i j t o m a r . E , T h e e f f e c t o f l i g h t a n d w a t e r p o t o n t i a ) o n d r y n u t t e r p r s i d u c i i o n o l l n d l i r o p s ,1 9 7 s l I n ; P l a n t R e s p o n s e t o C l i m a t i c F a c t o r s , e d . R . O . S l a t y e r P r o i . U p p s . i l a S v i n p . I p 7t i .

U i i e s c o , P a r i s , p . 3 1 3 - 3 1 6 .

f i I I t e m s P . E . D e r i v e d m e i e o r o l o g i c a l d a t a ; t r a n s p i r a t i o n , P r o c . B t m p . A a r o c I t m . W e l l . , ,1 9 w 3 R e a d i n g , 1 ^ . p . 3 5 - 7 2 .

R i j t e m a P , F , O n t h e r e l a t i o n b e t w e e n t r a n s p i r a t i o n , s o i l p h y s i c n l p r o p e i - t i e s a i u l i r o p p r o - h u t i o i 1 9 6 9 a s a b a s i s f o r w a t e r s u p p l y p l a n s . I n : S o i l W a i e V , P l a n t . V e r s l , M e d w l . c o m m .

H y d r o ! . O n d . T N O ) 5 , ‘ s G r a v c n h a g c . p . l i P - 3 8 .

R i j t e m a P , E . a n d A b o u k h a l e d A , C r o p w a t e r u s e . I n : R e s e a r c h o n C r o p W a t e r U s e , . S a 1 11 9 7 3 A f f e c t e d S o i l s a n d D r a i n a g e i n t h e A r a b R e p u b l i c - o f F - g y p t . A b o u k h a l e d A , , A r a r A , ,

B a i b a A . M . , B i s h a y B . C . , K a d r y L . T . , R i j t e m a P . P . a n d l a b o r A . I - A O R c g i o n n l O f f i c e f o r t h e N e a r L a a i . p . 3 - 6 1 .

S a l t e r P , f , a n d O o o d e J . E . C r o p r e s p o n s e s t o w a t e r a t d i r i o r o n l s t a g e s o f g r o w t h . p . * e n c i - 1 9 6 7 R e v i e w N o . 2 . C o m m o n w o a l t h B u r e a u o l H o r t i c u l t u r e a n d P l u n t . i t i O M i . r o p - , 1 . i - . i

M a i l i n g , M a i d s t o n e , K e n t . C o t n m o n w e a l t h A g r i c u l t u r a l B u r e a u , l a r n h i i m R o y a l ,B u c k s , E n g l a n d , 2 / 6 p .

S h a l b c v e i ] . e t a l . I r r i g a t i o n o f f i e l d c r o p s a n d o r c h a r d c r o p . * u n d e r » e m i - n r i d i o n d H io n s . I n t .1 9 7 6 I r r T I n f o . C e n t r e . N o . 1 .

S h i m s h t D , , B i e l o r a i H . a n d M n n l e l A , I r r i g a t i o n o f f i e l d t r r i ' S . i n : I c o l o g u a l S t i u l . o i .1 9 7 3 A n a l y s e s a n d S y n t h e s i s . V o l . 3 , 4 ) - B . Y a r o n e t _ a _ ! . p . J 7 7 - , i 8 ! .

S i t / n m L , M a M m i r a i i o i i o f a r a b l e c r o p v i e l d s i n t h e N e t h e r l an.) - . N c t f - I . A g t n , ' ^ c j . L '

1 9 7 7 2 B 7 .

S i d i C . b . I r r i g a t i o n o f v e g e t a b l e s . F A O H o n ( N A t / 66/ 2 : 3 , R o i r n . ’ .1966S t m m o n d s N . F . . C c i l ) E v o l u t i o n o f C r o p P l a n t s , l . o n g i n a n , l o m f o u . N e w Y o r k . . t . H ’ ) . .1 9 7 6

L f f e c l s o l s o i l m o i s t u r e s t r e s s a t d i l l e r e t n p e r i o d s c t g i c w i . o t s o r u eS i n g h R . ai id A l d e r f e r R . B . L f f e c t s o l s o i l n n : 1 9 W v e g c l H b l e s . S o t l S o i . 1 ( 1 1 f 1 ) ; 6 9 - 6 < i .

S la bb e r .s P , j . S u r f a c e r o u g h n e s s e f c r o p s atwl p o t e n t i.i 1 e v u p o i r an spi i at leu . 1. 11 v.l n u . ti. ; 1B i1 9 7 . ' 1 “ 1 .

S l a b b e r s P . ) . and D o o r e n t j o s ] . D c te r -m in a i i 1972 S e e I 'A t l .

o f c r o p w a t e r req -i i rc-inent * l o r luHil p ro p - , t

. S l a b b e r * P . J , i 8 o r b e l l o V . a n d S t e p p e r M . t v u l u a t i o n e l s i m p l i l i e d w a t e r . i r o j i y i e l d m o i i . H ^ .1978 A g r i e . W a t e r M a n a g e m e n r . f in p r e . » s >

S l a t y e r R , C 1 . 1 l i e e f f e , t o f l u l c m a l w a t e r s t a t u s o n p b s n l g r o w l l y d e v e k ] m e ’ l i t . n d 11 c ) . ! . I i : I H , . . 1I 9 7 J" R e s p o n s e t o C l i m a t i c l a c t o r s . e d . R . O . S l a t y e r . f r o - . , f p | i - c i l a S . t P i | i , H i i ’ , t . u c - . o ,

P a r t s , p . 2 6 ) - 2 , 7 / .

S l a t v e r R . O , P l a n t W a t e r R e l a t K ' n a h i p . s , A c a d e m i c I ' r e s ^ , Londoti n i i - t N . 'w Y . - r h . .d t j j , , l o t ' . 7

S o r b e l l e V . R . A r e v i e w o f s i m p l i f i e d c r c p - w n i e r p r i v lu c t i o n fi iuc t c-'i. * , w i th u pr-.- [.osal t c t iiu,'.|i (971. f i c a l i o n . I n t e r n a t i o n a ) I n s t i t u t e f o r band Rccb im . i t i o r i and Irnj.r.’ v om c .i 1 HI W l l . W . i g c . i i 1

I n t e r n a l c o m m u n ic a t i o n .

Sr . i i ih i l l C . S i r n p l i l i e i l a g r o c l i m a t i c p r o c e d u r e s f o r a s s e s s i n g i b c r i l e . ' o l w . i ' c r -.ij.td , . 1 ; ! ’ l.e,t19 /3 R e s p o n s e t o C l i m a t i c 1 a r t o r s , e d . R . O . S l a t y e r . 1 r o . . I ’ p p s a l a S v t . i j . H i : ' i I ’ i , . . . . . ,

P a n s . E c o l o g y a n d C o n s e r v a t i o n 3 - p . 2 , 0 1 - / 7 0 .

S t a n h i H T h e e l f c c t o f d i f f e r e n c e s i n s o i l m o i s t u r e s t a i n s o n p l a n t g r o w t h : A r e v i r w . u i d19.17 a n a h s t s o f s o i l m o i s t u r e r e g i m e c r p e n m e n t s . S o i l f s t i . B i : 2 i ) 3 - 21 / .

APPENDIX IV

D . W , ir' . t . ir . l i . i ' , 1.'; . . . r . . S . . ' I -AO .

:i i T ‘ . I . 1 r r i ^ a l ;^ii <ifm) *-(St 1 r I 'tti i i - i . ' . r . - W a iLT af iJ 1 111 ’ . 1 a ' i !,(■'v ' . 1 , i.'i. i| . . I ' . . ' . M . m I m ' i . l - > . S , . r r i J O f V i ’ f l . i , - . I ' l ' f l n , . I , .

■r I. .1 / ) . 1-. L rtrt.ili.HlLi . . I,- ^' ipfj ' . rtiiil I . f t p(. ' t ' . , - Il , , A. t . . I . : I 1 ij I .. t .X i .I'n.v.

r>. I. .-I. I , '• , [ >.i' ill. ,., 1 o f i i " ' i| ) f i 111 i .fi- •■.. lai.i j f . . *■' I . . .Ii’ vvlppr-.ef . i ar..i , i i !o . l i . : P 1 j i . iy o - (H ' l i . o (o I. l i 'n i i i i L I in t. . ,.,1 . S IB I vi’ r f" . . f r o , . ".1 ' I 1 t * ' i , V s T ; 1 .

11.Iiiorii' I / . II 1,1 . ari l f. . M . -I.’ V.1-., ! I.o iHlpi t ol 'Oi. 'tioi -t , re on the ^rovih ..il-I . ioI I .1 i i*,(etj

' i r o p - . I ' \ W l . ' . h , H u l l . t : . ' W r t ^ c - i . i [ . . ( e i i .

I' M l ', .1 i e ; i ) , I' . at-t ' ' ' . I t ■,o r y , i . ' . M t c . t o l j tFi iO it 'h.■ n . o i iL ' t 'n irai ion i*( v j t e i i . i p o o r .mo i. ' ^ . 11 ; . t e m . i i . i t r in . i.|ji r aii. '-, , | - ! . o ic . 'M i tho ' i i r e l a t i o n s h ip . o l r o t ton It 'rtvoi . . A « r i r .

. M o ' o i . r o i O i ( \ 0 : ^

'■ li ni.i u- .. r. I .*. .f r.. ■ ; 1 ,,fi , A I, [ -■ .11 Ol).. (i I 'ill rr ov . A LI i n e . t. it,. n i(0 . Ji)!. ].,

I .1 r e . y , I ' . !J vnan, i . ' , iin, lot lOii o I p I jr.t ji ro#> h . P j 11 1 : 11 nvc lopmen l ot ii rno.l o l . 1 r im ' . A S A I'I ’ l I IL

1 n i r , R .H , rti.H I hon 1 ,11. Dvnii/ttK ' i mu la tio ii ol [.l.n.t .[ro w ih . F a rt 11: I . 0 r])O rai ion ol a r lu n )1'F‘ t fd iK loea ifio r anJ p a rtitio n in g ; o f tic l p h o tO 'v r. ih .tie . T ra n s . ASAP l i : l ] 7 i )

V. I j iH i-iiii' N ,G . . .N'.uii oil l ira , H t ik k e ri F . .inH V .unailevaii V . K , Revi pw o( w o rk .Jonr on w a te rI r i ' i ' i . rern.-iit s o t ro p ’i in India , ihd i Jii A ,( r ir . Res . In s t . , iJ iv , A ( ro n , , New 'U ’ lh i • 1

o r N rtva t.iin rn i r'raka shan ( I 'u h l) . , 7(ie I tn J h w n r, Poona-J.

D o 'AtI t r , I . [ t y n a m i . r o n c e p t s m t n o l o t v , In ; F r e d i i n o n an d W e a s . i r o m e i i t o t P h o i O ' v n t h o t i , 1 )l -I f 'r . . . . l : i . t i v i t v , P r o o . I K F ' V F T e . ; , , . W l . ; . , I r o ' . o n . l i . 2 I S e p i e t n b e r

i i o iWii I . I , F la i i i p ro H i ., 1 lo r .. M i n e l lajis'on s I ' a p e r s l a n H h o u w M Oi^e s . ' h o o l, W aj jemii een N o . I ;I - >i

■;o Wit t . I . Photo sv nil,O'I,K o) loji rji.op.es, A jm . Res. Rep 6til, Fn.Jor , 'Vaaon innei,. ,V p.

. b ' ,V ' i . I , 1 r a i l ' p i r at ion and r r e p v i e l j s . V o r s l - 1 an.l bk and i ij O i p l e r z , , i t l (b' ). F n i l e . ,l‘t/C Wd,t'''i>tiS''n.’ j o . i n ' . b o s I, A i ( r o m e t e o r o l o j j i i ai l i e M ' t a t t o t i s . S e e ( A O .

i J o o r e n t i r i s [ , a n d 1 n m t W . b i , b r c i i w a t e r r e i i m r e m e n t s . S e e P A G ' ,197 r

D l w i O’, ! , A . V a t o r - M O l d r e l a l i e n l o r non ) o r a . ; e ire> i . s. |, I r r i o a t t o r i anrl O r n in a o c D ’ VistI ’ l/o .*isi I . ■Wt i p ; . ; i : i .

■(■I Nrtili A . i i , I he ' n in . 11 . am e r.I loa l .irt'tt .n cs r tpo t r .m ip i r a i l .'11. A n i r t l ' i D o ia n v iS ( i d O ’ lR' i>!:.i I Nadi A . i l , ittnl K lieir H .M . An apprat sal of t(ie met oo rologi. a I ,ip]>roa,_|i for tsses.sii,^ ei apor.i I'.ft'J lion under iropieal eonJ111eti.s , Ind ian Afjr it . J, i ( J): .1?- Jl7.h A v ' , Ai^re - e i oK 'H i. al / o n e F r o t e r i . S o i l R e s e u r r e . s R e p o r t N o , .',6 . Rotr; I'I'd

i A G , W . it e i i fu a tn v t o r a i jr i eul l u r e , R , ,S . A y e r s ar» l D , W . W e s t r o t . i t r i i(al .On and D r a in a j i el d ’ (. F . i p e r N o , J ' ) , ' R o m e . 97 p .

( Au'. A ( ro - m e t o o r o l o j ; ! ' at fie ld s t a t i o n s . I, D o o r c n l i o s . I r n j i a t i o n und D rum ajte Paper so. JT, I ’ l I. R o ’ i ie . dd

h A t , ’ . 1, rop w a t e r r o ip n r em ent s . ) , D o o r e t t b o j and W . C . P r u t t t . I r r i f l a t i o n and U r a i t i a j * P a p e r l i f T ” ‘ l o . dd. ( r e v i s e d ) . R o t f i e . l i t p .

FACt . D e t e r m i n a t i o n o f e r o p w a t e r r t\ |u ir en ien ts t o r f i e l d p r o j e e t s . S l a b W r s P . l . and I. 197d D o o r e n b o a . In ; W a t e r Dse S e m i n a r Damaseus. I r r i g a t i o n and Draitiaf;e V a p o r N.

R o m e . p . b l ' 7 d .

l A O . p p o d u f t i s ' t i Y e a r t w o k I97 t ' . V o l . AU. R o m e , itj;?F A G ) ' I A t A . S o i l - m o i s t a r e a n d i r r i R a n o n . . l u d i e .s I I . P r o e e e d i K j ! . ' o f a p a n e l h e l d >n V . e n n a ,1979 e r t j a n t/ e d by the Joint F A O ' I A E A D t v i s i o n o f Atomii . ( n e r a y iti P oo d and A y n , u l tn r e .

f A O I A t A . S o i l - mot sCure and i r r i g a i io.ti s i t i d ie s I . P r o i e e d i t i a * o f a p a n e l he ld in V . ini iia , 19ti7 l i - l S M a r c h 196b.

l e d d e s R . A , W a t e r , l ieat and c r o p g r o w t h . M e d e d , I and b o u w h o g e s s hs'O I , W a g en i r ig en . " K l . ' ) , 1971 ItW p .

F e d d c s R . A , and K o w s l i k F’ , S im u la t i o n o f f i e l d w a t e r u p tak e and t r o p g r e w i l i a s in r i i i e r i f e d by 1976 a o i t p h y s i c a l p r o p e r t i e a , ( I n p r e p a r a t i o n )

I-IS her R.A, and Haoan ft ,M . Plant water relations , i rnaal i on m ana gem cut and < rs'p vi t'Ul. F »p.196a Agrie. 1;(61-1?7.f i t ^ p a t n r k E . A . and N i s H . A , T h e e l im a t t c ( a c t o r ih A u s t r a h n n g r a s s l a n d t 'cs i lo i jy . A u s t t a l i a n 1970 G r a s s l a n d s , C a n b e r r a . A u s t r a l i a n N a t i o n a l U n i v e r s i i e P r e s s . p . ,1-96.

F i t z p a t r i c k E . A . and N i e H . A . A m o d e l f o r s u n u la tm g s o i l w i t t e r r e g i m e in a l i o r n a t e t a t l o w - c r o p 19t>9 s y s t e m s . A g n c . M c t e o r o l . 6 ; 3 ( 1, V J 1 9 .

F l i n n J , G . T h e s i m u l a t i o n o f c r o p i r r i g a t i o n s y s t e m s . C h a p t e r 7 , . S y s t e m A n a l y s i s i n A g r i . u l m r a l 1 9 7 1 M a n a g e m e n t , s v l . D e n t a n d A n d e r s o n . I n t e r n a t i o n a l t d i l i o n . W i l e v .

F o g e l M . M . O p t i m u n i c o n t r o l o f i r r i a t * H < J n w a t e r a p p l i c a t i o n . J . H y d r o l o g y

1 9 7 1

G a a s t r a P . P h o t o s y n t h e s i s o f c r o p p l a n t s a s i n f l u e n c e d b y l i g h t , c a r b o n d i o m d e , t e m p e r a t u r e a n d 1959 s t o t t i a t a l d i f f u s i o n r e s i s t a n c e . M e d e d . L a n d b o u w h o g e s c h o e l , W a g e n i n g c n , 5 9 ( 1 ' ! ) *

H a d a s A . , S c h w a r t z c n d r u b e r D . , R i ) t e m a P . E . , F u c h s M . a n d Y a r o i i D . t e d s ) . F h v s i i a l A s p e c t s 1 9 7 J o f S o i l W a t e r a n d S a l t s i n P c o s y s t e m s . h c e l o g i c a l S t u d i e s N o . 4 . S p r i n g e r V e r l s g ,

B e r l i n , H e i d e l b e r g , N e w Y o r k . 46O p .

H a g o n R . M . , H a i l * H . R . a n d E d m i n s t e r T , W , I r r i g a t i o n o f a g r i c u l r u r a l l a n d s . A g r o n o m y S e r i e s 1 9 6 7 N o . 1 1 , A m e r . S o c . A g r o n . , M a d i s o n , W i s c o n s i n .

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S h m u c l i F . e t . ^ * C i t r u s w a t e r r e q u i r e m e n t s e x p e r i m e n t s c o n d u c t e d i n I s r a e l d u r i n g t h e 1 9 6 0 ' s . I n :1 9 7 , 1 E c o l o g i c a l S t u d i e s N o . 2 . S p r i n g e r V e r U g . p . . l J 9 - J ! i n a l s o p r e s e n t e d a t S y t n p o s n i m o n

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19f 'l

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A m i r ) . a n d B i e l o r a i H , T h e i n f l u e n c e o f v a r i o u s s o i l m o i s t u r e r e g i m e s o n t h e y i e l d a n d q u a l i t y e f1 9 6 9 c o t t o n i n a n a n d x o n e , J . A g n c . S c i . , C a n b e r r a , 7 . ^ • . 2 7 9 - 2 2 9 .

A r a n d a J . M . E f f e c t o d e l r e g i m e n d e r i e g o s s o b r e e l r e n d i m i e n i o y a d e l a n t o d e c o s e c h a d e l a l g o d o n .1966 A n n . E d a f o l . A g r o b i o l . ( M a d r i d ) , 2 5 : 3 1 3 - 3 2 2 .

A r a n d a J . M . a n d M a c i l l a N . F . E f f e c t o d e l r e g i m e n d e h u m e d a d d e l s u e l o s o b r e l a p r e c o c i d a d v 1 ^ 9 p r o d u c c f o n e n a l g o d o n d e r e g a d i o . A n n . E d a f o l . A g r o b i o l . ( M a d r i d ) , 2 o : 1 - 1 3 .

A r a r A . T h e e f f e c t o f u n d e r g r o u n d w a t e r d e p t h o n t h e y i e l d a n d w a t e r c o n s u m p t i o n o f c o t t o n . I r n - 1 ^ 3 g a l l o n a n d S a l i n i t y S t u d i e s R e p o r t N o . t O , M i n i s t r y o f A g r i c u l t u r e a n d A g r a r i a n R e l o r m ,

S y r i a n A r a b R e p u b l i c .

A ^ h a r A . C . a n d N u r - U d - D m A h m a d , u ' o n a u m p t i v e u s e a n d a p p t i c a i i o n e f f i c i e n c y u n d e r d i f f e r e n t1 9 6 1 i r n g a t i o n p r a c t i c e s . P a k i s t a n J . S c i . R e s . , 1 3 ; K ) 6 - 1 H I .

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H e n n e t t 0 . 1 . . , t r i e l . J . a n d M a c K e n / l e A . J . B o l l , f i b e r a n d s p i n n i n g p r o p e r t i e s o f c o t t o n a s a f l c c t i H l1 9 6 7 b y m a n a g e m e n t p r a c t j c ' . ' s . T e c h . B u l l , N o , 1 3 7 2 , A g n c . R e s . S e r v . I ' S D A i i i c o o p i ' r o i i i ' i t

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B i e l o r a i H . f h c i r r i g a t i o n o f c o t t o n . I n ; E c o l o g i c a l S t u d i e s . A n a I y s i s a n d S y T i i h e - . ! s V o l , , . c d ,1 9 7 3 B . Y o r o n e t . a l . S p r i n g e r V o r l a g , B e r l i n , H e i d e l b e r g , N e w Y o r k .

B i e l o r a i H , a n d S h i m s h i D - T h e i n f l u e n c e o f I h e d e p t h o f w e t t i n g a n d s h o r t e n i n g o l t h e i m g n i i o u 1963 a e a s o n ^ o n t h e w a t e r c o n s u m p t i o n a n d y i e l d s o f i r n g a t e d c o t t o n . I s r a e l ] , A g r u . R e s . ,

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o f A r k a n s a s , F a y e t i e v n U e ,

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B r u c e R , R . a n d S h i p p C . A . C o t t o n f r u i t i n g a s a f f e c t e d b y . s o i l m o i s t u r e r e g i m e . A g r o n o m y J , , 5 2 ;1962 15-18.C r o w i h e r F . S t u d i e s i n g r o w t h a n a l y s i s 0/ t h e c o t t o n p l a n t u n d e r i r r i g a t i o n i n t h e S u d a n . 1 . 1 h e1 9 3 2 e f f e c t s o f d i f f e r e n t c o m b i n a t i o n s o f n i t r o g e n a p p l i c a t i o n s a n d w a t e r s u p p l y . A n n . H o t .

( L o n d o n ) , 2 8 ; 8 7 7 - 9 1 2 .

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D o a a D . B . a n d S c a r s b r o o k C . E , E f f e c t o f i r r i g a t i o n o n r e c o v e r y o f a p p l i e d n i t r o g e n b y c o l t o n .1969 A g r o n o m y J , , 6 1 : 3 7 - i O .

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F a r b r o t h e r H . G , A n a n a l y s i s o f t h e w a t e r - r e l a t i o n s o f e l s c o t i o n g r o w n u n d e r s i m u l a t e d s p a t e -1 9 7 6 i r r i g a t i o n . C r o p w a t e r u s e s t u d i e s a t E l R o d , A b y a n D e l t a 1 9 6 1 / 6 2 . R e p r i n t e d :

■ R e g i o n a l F i e l d F o o d C r o p s P r o j e c t ( I r r i g a t i o n A g r o n o m y ) o f t h e N e a r - F a s t R e g i o n .F A O , R o m e ,

I ' u i ' h . M . , H a u . i . n b . r i ; 1 . a n d S t a n h i l l G . A h o l d t m i o f t h « c o n t r o l o T c o t t o n i r r i g a t i o n p r a c t i c e 1 9 t > 4 f r o m i . ' l a s « A p a n d a t a . U r e a l [ . A g n c . R e s . , l / : 2 3 7 - ^ ^ 9 -

h u c h ^ M . a n d S t a n h i l l t . l . T h e u s e o f C l a s s A p a n e v a p o r a t i o n d a t a t o e s t i m a t e t h e i r r i g a t i o n w a t e r 1 9 6 3 r e f i l l r e m e n i s o f t h e c o t t o n L r o p . I s r a e l J . A g n c . R e s . , 1 3 ( 2 ) t 6 3 - 7 S -

C e r a r d C . J , a n d N a m k e n I , N , I n f l u e r u e a f s o i l t e n t u r e a n d r a i n f a l l o n t h e r e s p o n s e o f c o t t o n t o I 9 6 0 i n o i s t u r e r e g i m e , A g r o n o i n y J , , 5 8 ; 3 9 - i 2 .

G i p s o i i ) . R . a n d J u h a m I t . t . . I n t i n o n c e o f m g h i t e m p e r a t u r e o n g r o w t h a n d d e v e l o p m e n t o f c o t t o n 1 9 ^ f G o s s V P m m h i r S U E u m I . 1 . F r u i t i n g a n d b o d d d e v e l o p m e n t . 1 1 . F i b e r p r o p e r t i e s .

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C r i m e s O . W . , D i c k e n s L . , A n d e r s o n W . a n d Y a m a d a H , I r r i g a t i o n a n d n i t r o g e n f o r c o t t o n . C a l i f .1 96 7 A g n c . , 2 U 1 1 ) : 1 2 - U .

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t l . Y i e l d c o m p o n e n t s a n d q u a l i t y c h a r a c t e r i s t i c * . A g r o n o m y ] . , 6 l : 7 d 9 - 7 ? 6 .

M a m i D o n S t a n b e r r y C . O , a n d W o o t t o n W . M . C o t t o n g r o w t h a n d p r o d u c t i o n a s a f f e c t e d b y m o t s -1976 t u r e , n i t r o g e n a n d p l a n t s p a c i n g o n t h e Y u m a M e s a . P r o c . A m e r . S o i l S c i . S o c . , 2 0 :

2 i 6 - 2 S 2 .

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1 9 ‘5 7 1 2 i 3 I 7 . 3 3 i .

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M e t e l e r k a m p H . R . R . a n d C a c h e t l k . E , F f f e c t * o f m o i s t u r e s t r e s s o n e v « i o l r a n s p i r a t i o n a n d g r o w t h 1970 o f c o t t o n ( G o s s v n i u m h i r s u t u m ) . R h o d e s i a n ] . A g n c . R e s , , 8 : 4 7 - 5 5 -

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M l t l l e r C . C o l t o n , c u l t i v a t i o n a n d f o r t i l i l a t i o n . S e n e s o f M o n o g r a p h s o n T r o p i c a l a n d S u b t r o p i c a l1968 C r o p s . R u h r - S t i c k s t o f f , A k t i e n g e s e l U c h a f t , B o c h u m ,

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S t o c k t o n J .

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G R A P E

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p E . , S i m p s o n B . ] . a n d W h i t e h u r s t S . H . S h o r t - s e a s o n , n a r r o w - r o w c o t t o n s i u d i e . s i n i h c n o r t h e r n b l a c k l a n d * . T e x a s A g n c , E x p . S t a . , T e x a s A 4 M U n i v . P r o g . R e p . P R - 3 3 8 2 ,

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H o w e 0 , W . a n d R h o a d e s H . F . I r r i g a t i o n p r a c t i c e f o r c o m p r o d u c t i o n i n r e l a t i o n t o s t a g e o f p l a n t 1955 d e v e l o p m e n t . P r o c . S o i l S c i . S o c . A m e r . 1 9 : 9 4 - ^ .

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B r o w n I ' , 1 . and S h r a d e r W . D . G r a i n y i e l d s , e v a p o t r a n s p i rat ion anil w a t e r 11 s o c t h , icuc i ol g r . u u1959 s o r g h u m u n d e r d i f f e r e n t c u I t u r a l p r a c t i c e s . A g r o n o m y j . , | 1 :3.V>-.*2,t .

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l a lh . i M . T h e r e s p o n s e v>l M e x i c a n and l o c a l w h ea t v a r i e t i e s to i r n g a t i o n r e g i m e and n i t r o g e n 1 9 7 / I c r l t h i e r . |, Y i e l d , A g r o i h i m 1. .a , ] B ( 3 ) ; i / t ' - /

Ta lh . i M . T h e r e s p o n s e vif M e x i c a n an.l t o s o f w h ea l v a r i e t i e s 10 i r r i g a t i o n rv ' g ime .md n i t r o e c i .1973 f e r t i l i x e r . U , W a t e r c on sunipl 1 v e u s e and e f f i . i e n s v o f wa l o r u s e . A gi oc li 1 m 1 ca , I 9 ( i ' ) ;

£ 9 1 - / 9 7 .

W a r d i ' r 1 . 0 . , 1 e h a n e J . J . , H inm an W , v i , and S t a p l e W , ] . f h c e f t e v l o l f e r t i l i s e r on g r o w l b .19( '3 n u t r i e n t u p ta k e and m o i s t u r e u s e o f w h ea t on tw o s o i l s in S o u t h w e s t e r n S a sk . i t i l i ew . it i .

C a n . ] . S o . l B c i . , £ 3 : 1 ( 1 7 - U b .

W i l l son D . J. , 1 h o m e G , N , a rid h r e n t h S . A . W . A n a l v * i > o l g r o w 1 1: and yn e ld o l w i n t e r m d *; >r: ng1963 w h e a l . A n n . ol B o tn nv , N . S . , 27( l o 3) ; I - 2 2 .

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Y a ro i l D. , Stra teener C, , Shuns hi I ), and Wei s bred M . Win-.11 respoii se lo -.oi I rie 1 n f - .m.l i!.,'1973 optim.al irr igallon policy unilcr i otidi tiens el tin si.ab le rairil.ill. Water Re*'ouri e* Re * . .

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