response of bulb yield and yield components of onion (allium cepa l) for deficit irrigation in...

Mekelle University

College of Dry land Agriculture and Natural Resources

Department of Dry land Crop and Horticultural

Science

Response of bulb yield and yield components of onion (Allium cepa

L) for deficit irrigation in Antsokia Gemza Woreda, Eastern

Amhara

By

Teshome Nega Shumye

A thesis

Submitted in Partial Fulfillment of the Requirements for the

Master of Science Degree

in

Dry Land Agronomy

Advisor: Solomon Habtu

(PhD)

January, 2011

ii

ABSTRACT

In arid and semiarid areas where agricultural development is severely constrained by

water scarcity and its mismanagement, the need to use the available water efficiently

is unquestionable. The purpose of this study was to investigate the response of onion

for deficit irrigation. The field experiment was conducted at Antsokia Gemza woreda,

eastern Amhara. The treatments consisted of four irrigation levels (25%, 50%, 75% and

100%ETc) that each were applied at four developmental (establishment, vegetative

development, bulbification and ripening) stages and throughout the developmental

stages. It was laid out in RCB design with three replications. Variation in amount of

applied irrigation water either at specific or throughout the crop developmental

stage/s/ had very high significant (P< 0.001) effect on yield and yield components of

onion. Plant height, leaf number, fresh biomass, total bulb yield, unmarketable bulb

yield, average bulb weight, bulb diameter, number of bigger and medium bulbs and

percentage of bolting were increased linearly with increasing irrigation amount. The

highest total bulb yield (26t ha-1) was obtained from treatment 100%IIII and the

highest marketable yield (23.5t ha -1) was obtained from treatment 75%III0. Treatment

75%0III, 75%III0 and 50%III0 gave none significantly different total and marketable

yields from 100%IIII. The severe yield reduction was obtained in treatment 25%IIII

(3.8t ha-1) and 25%II0I (6.9t ha-1). Bulbification stage was the most sensitive stage for

water deficit. On the other hand, water deficit during establishment or ripening stage

iii

had a limited effect on yield. Water productivity of onion was increased from 2.16% in

treatment 75%0III to 6.47% in treatment 75%IIII compared to 100IIII. Hence,

application of deficit irrigation either at establishment or ripening stage is good

option to save water without significant bulb yield reduction. Application of 75%IIII

can be a good option in water scarce areas to increase the irrigated area as a result of

its high crop water productivity.

Key words: onion, developmental stages, deficit irrigation, crop water productivity

iv

Acknowledgement

I would like to express my sincere and profound gratitude to my

advisor Dr. Solomon Habtu for his invaluable guidance,

encouragement, unreserved support and constructive comments

throughout the thesis work.

I would like to extend my sincere gratitude to Antsokia Gemza

Woreda Agricultural and Rural Development Office giving me the

chance to upgrade my education level. I am also grateful for

Rural Capacity Building Project for covering all the financial

expenses of the research and without which, the completion of

this research work would have been impossible. I also extend my

gratitude for Ethiopian National Meteorology Agency, Kombolcha

sub branch for providing Class ‘A’ pan and weather data of the

research area.

I wish to extend my special thanks to Dr. Fetein A., Mr. Dejenie

K. and, Mr Samuel T, Lecturers in Mekelle University for their

assistance and critical comments in the manuscript.

v

I would like to express my special thanks to my colleague

Teshome Mulugeta for his unexpressive support by giving his PC

for writing this thesis. The generous support and encouragement

of Mr. Getnet A., Ms. Aynalem K., Mr. Birhan B. and Arega Z, and

all my colleagues, friends, families and relatives are deeply

acknowledged and emphasized in all cases of my future life.

Finally, I would like to extend my sincere thanks to my beloved

wife Genet Mengist who had great participation and overall care

and support during my study.

Dedication

vi

To my candle of hope and light when

blindness and darkness

overwhelmed the atmosphere around me,

to my fallen angel, to my mother Asnakech

Abera.

vii

Acronyms

OM Organic Matter

OC Organic Carbon

pH Potential of Hydrogen

FC Field capacity

Av.P Available Phosphorus

CEC Cathion Exchange Capacity

EC Electrical conductivity

CSA Central Statistic Authority

ANOVA Analysis of Variance

CV Coefficient of Variation

TAW Total available water

RAW Readily available water

WVE World Vision Ethiopia

FAO Food and Agriculture Organization of the

United Nations

WUA Water users association

CWP Crop water productivity

GDP Gross domestic product

ETo Evapotranspiration from a reference crop

ETc Evapotranspiration from the crop

Kc Crop coefficient

Estabt Establishment stage

viii

Veg. devt Vegetative development stage

Bulfn Bulbification stage

Ripen Ripening stage

Av. Average

Wt Weight

t ha-1 Tons per hectare

AGWARDO Antsokia Gemza Woreda Agricultural and Rural Development Office

ix

Table of Contents

DECLARATION. ......................................................II

ABSTRACT.........................................................III

ACKNOWLEDGEMENT................................................IV

DEDICATION......................................................V

ACRONYMS.......................................................VI

LIST OF TABLES.................................................IX

LIST OF FIGURES.................................................X

CHAPTER ONE: INTRODUCTION......................................1

1.1. BACKGROUND AND RATIONALE.....................................1

1.2. STATEMENT OF THE PROBLEM.....................................4

1.3. OBJECTIVES OF THE STUDY......................................6

1.4. HYPOTHESIS.................................................6

CHAPTER TWO: LITERATURE REVIEW.................................7

2.1. ONION PRODUCTION OVERVIEW....................................7

2.1.1. Agronomic characteristics of onion..............................7

2.1.2. Economic significance of onion production........................8

2.1.3. Onion production in Ethiopia..................................9

2.1.4. Optimum growth environments of onion.........................10

2.2. IRRIGATION DEVELOPMENT AND MANAGEMENT.........................11

2.2.1. Irrigation development......................................11

2.2.2. Irrigation scheduling: the tool for water management...............13

2.2.3. Farmers experience on irrigation scheduling and water management in the

study area...............................................16

x

2.2.4. Concepts of deficit irrigation..................................18

2.2.4.1. Influence of deficit irrigation on yield and yield components.......20

2.2.4.2. Influence of deficit irrigation on crop water productivity..........23

CHAPTER THREE: MATERIALS AND METHODS.........................26

3.1. DESCRIPTION OF THE STUDY AREA...............................26

3.1.1. Location................................................26

3.1.2. Climate.................................................27

3.1.3. Soil ....................................................27

3.1.4. Farming system ...........................................28

3.2. TREATMENTS, DESIGN AND AGRONOMIC PRACTICES OF THE EXPERIMENT.....30

3.3. DATA COLLECTION AND ANALYSIS................................32

3.3.1. Analysis of soil chemical and physical properties..................32

3.3.2. Reference evapotranspiration, crop water requirement and applied

irrigation depth................................................34

3.3.3. Crop parameters..........................................40

3.3.4. Statistical analysis.........................................41

CHAPTER FOUR: RESULTS AND DISCUSSION.........................42

4.1. PLANT HEIGHT..............................................42

4.2. LEAF NUMBER...............................................43

4.3. FRESH BIOMASS YIELD........................................44

4.4. TOTAL BULB YIELD..........................................46

4.5. MARKETABLE AND UNMARKETABLE BULB YIELDS.......................49

4.6. AVERAGE BULB WEIGHT........................................51

4.7. BULB DIAMETER.............................................53

4.8. WEIGHT AND NUMBER OF BULBS FOR BULB SIZE CLASSES..............54

4.9. BOLTING.................................................58

4.10. HARVEST INDEX............................................59

xi

4.11. CROP WATER PRODUCTIVITY....................................60

CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS..................64

5.1 CONCLUSION.................................................64

5.2 RECOMMENDATIONS.............................................66

REFERENCES.....................................................68

APPENDICES.....................................................78

APPENDIX A: METEOROLOGICAL DATA..................................78

APPENDIX B: IRRIGATION RELATED DATA...............................84

APPENDIX C: MEAN SQUARE TABLES FOR ANALYZED PARAMETERS...............87

BIOGRAPHICAL SKETCH............................................89

List of Tables

xii

2.1. Irrigation frequencies in some assessed kebeles.............18

3.1. Average yields and area coverage for the major irrigated crops.

..............................................................29

3.2. Types of irrigation scheme and their respective irrigated area

in 2008 & 09..................................................29

3.3. Treatment combinations for irrigation amount and crop

development stages............................................30

3.4. Properties of soil analyzed and methods used................33

3.5. Some soil chemical properties of the experimental site......33

3.6. Some soil physical properties of the experimental site......33

3.7. Reference evapotranspiration and crop water requirement of

onion per decade..............................................36

3.8. Break down of total applied irrigation water to developmental

stages of onion...............................................40

4.1. Amount of water, developmental stages and their interaction

effects on fresh biomass, total bulb yield, marketable and

unmarketable bulb yield of onion..............................50

4.2. Amount of water, developmental stages and their interaction

effects on

mean bulb weight of onion....................................52

xiii

4.3. Amount of water,crop developmental stages and their interaction

effects on mean diameter of onion bulbs.......................54

4.4. Weight of each bulb size classes and their corresponding

numbers as affected by irrigation amount, developmental stage of

the crop and their interaction................................57

4.5. The actual yield loss, calculated yield that can be obtained

from the saved water and net yield gain or loss compared to full

irrigation....................................................61

4.6. Water productivity of onion interms of total bulb yield and

marketable bulb yield.........................................63

List of Figures

xiv

2.1. Accumulated water over the surface of farmers field due to

over irrigation of onion......................................17

3.1. Location of the experimental site........................26

3.2. Mean monthly rainfall, maximum and minimum temperature and

relative humidity of the study area...........................27

3.3. Experimental field with onion plants at the end of

establishment stage of onion...................................32

3.4. Onion developmental stages, its duration days and the

corresponding Kc value........................................35

3.5. Refernce evapotranspiration of the experimental area by

using pan evaporation method and Penman-Montheith model.......37

4.1. Plant height measurement taken at the end of each

developmental stages..........................................43

4.2. Relation ship between applied water and fresh biomass....45

4.3. Weight of bigger and small size bulb classes per treatment

..............................................................56

4.4. Bulb size classes classified as small, medium, and bigger

size..........................................................56

4.5. Percentage of bolted onion plants per treatment..........59

4.6. Yield loss due to water deficit and yield gain from the

saved water...................................................62

xv

Chapter 1. Introduction

1.1. Background and Rationale

While on global scale water resources are still ample, water

scarcity and fragility, unequal distribution in space and time

and its mismanagement are an increasingly important issue in

many parts of the world (Farre and Faci, 2006). These problems

are mainly due to population pressure and fast urbanization as

xvi

well as industrial and agricultural development. Since the last

decades, the competition among water sectors is going to

increase also with the on-going climatic change and variability,

and land degradation and desertification processes. Despite,

Ethiopia is blessed with ample water resources in central,

western and south western parts; most of north eastern and

eastern parts of the country are relatively dry. In those parts

of the country, the distribution and availability of water is

erratic both in space and time. Furthermore, Ethiopia will

become a physically water scarce country by the year 2020

(Sileshi et al., 2005).

At the same time, the success of sustained agricultural

production largely depends on water availability. It is clear

that, irrigation water has increased food security and improved

living standards in many parts of the world; it has been

instrumental in feeding the populations of developing countries

in the last 50 years. However, water resources are not

distributed evenly around the globe; arid and semi arid regions

will continue to have conflicts over water supplies (FAO, 2002).

In addition to the decreasing supply of water, larger

xvii

populations in developing countries are expected to increase

total demand for food in the coming century. Those in developing

countries are eating more meat products, which require cereal

crops as food for livestock. Estimates by International Food

Policy Research Institute (IFPRI) showed that to meet demand for

consumption and livestock feed in 2020 world production will

have to increase 40% over 1995 levels (Zilberman and Schoengold,

(nd)). The great challenge for the coming decades will therefore

be the task of increasing food production with less water

particularly in areas with limited water, land resources and

inefficient water use (FAO, 2002).

The Ethiopian agriculture plays a dominant role in the overall

economic performance of the country, not only in terms of its

contribution to GDP, but also as a major source of foreign

exchange earnings, and in providing employment to a large

segment of the population. However, it is heavily dependent on

rainfall which is highly variable, both spatially and

temporally. It is hampered by recurrent droughts. The

variability of rainfall distribution, frequent dry spells and

droughts exacerbate the incidence of crop failure and hence food

xviii

insecurity and poverty. The erratic weather pattern is the major

factor for the variability and unpredictability of food

production in Ethiopia. There seems to be clear evidence that,

there has been below average rainfall in Ethiopia since mid

1970s (Warren and Khogali, 1992). According to Von Braun (1991)

a 10% decline in rainfall below the Ethiopian national long-term

average reduces national food production by 4.4%. Therefore,

better management of existing water systems along with the use

of more efficient irrigation technologies will be essential in

upcoming decades.

The current agricultural policy of Ethiopia is within a strategy

towards a more market-oriented agriculture at national and/or

international level. Horticultural crops play an important role

in this strategy as well contributing to the household food

security. The vegetable being cash crop with nutritional value

generate income for the poor households. Further, it provides

employment opportunities as their management being labor

intensive. However, higher profits can be achieved by increasing

the production of a particular vegetable throughout the year

when efficient irrigation system is used. Ethiopia has enormous

xix

potential to cultivate vegetables like onion on small scale as

well as commercial scale. Onion (Allium cepa L.) is the most

important cultivated crops in the country. It is an integral

part of Ethiopian dish. It plays a key role in the economies of

many households. Due to its high economic value, it is rapidly

becoming popular and the major vegetable produced in the farming

community of Ethiopia as a cash crop. It is popular among

producers because of the advantage of high yield potential,

availability of desired cultivars for various uses, ease of

propagation by seed, high domestic (bulb and seed) and export

(bulb and cut flower) markets in fresh and processed forms

(Lemma and Shimelis, 2003). The Ethiopian Central Statistics

Agency (CSA) report of the production year 2007/08 of meher

season indicated that the status of root crops produced and the

area under root crops production in the country was about 1.53

million tones and 184329 hectares respectively. Out of this

production, onion takes the share of 175106.1 tones and 18013

hectares (CSA, 2009). In Antsokia Gemza woreda, which is the

study area, onion is the major vegetable crop followed by

tomato. The area covered by onion in the years 2006, 2007, 2008

and 2009 were 675 (22.21%), 796.4 (24.87%), 1086.9 (30.55%), and

xx

1251.9 (32.5%) ha, respectively. Both onion and tomato are

exclusively produced under furrow irrigation. In the last few

years, the demand for onion production has shown a significant

increase in the woreda. However, the limited irrigation water

availability along with unwise use of the available resource

limits the area allotted for onion production.

To utilize the advantages of irrigation development, Ethiopia is

increasingly investing in this sector. In the past 20 years

various efforts have been made by the current government to

expand irrigation in the country. The country’s Agricultural

Development Led Industrialization (ADLI) Strategy considers

irrigation development as a key input for increasing

agricultural production. Despite the efforts of the government

to expand irrigation, the country has still not achieved

sufficient irrigated agriculture to overcome the problem of

endemic food insecurity and poverty. The total area under

irrigation in 2006 was reported to be 603,359 hectares (less

than 5% of its total irrigation potential) which is very small

per capita irrigated area (of about 30 m2) compared to 450 m2

globally (Sileshi et al. 2005). The same author indicated that

xxi

the per capita irrigated area only reaches 45 m2 per head by the

year 2015. This figure does not move the sector significantly.

Therefore, given extreme meteorological and hydrological

variability in the country, it is important that significant

attention to be given to enhance management of the water

resources and water productivity for better agricultural

production.

In the context of improving water use efficiency, there is a

growing interest in deficit irrigation, an irrigation practice

whereby water supply is reduced below maximum levels (FAO,

2002). The crop is exposed to a certain level of water stress

either during a particular period or through the whole growing

season (Kirda, 2000). The expectation is that any yield

reduction will be insignificant compared with the benefits

gained through diverting the saved water to irrigate other crops

(Eck et al., 1987). It can maximize water productivity for higher

yields per unit of irrigation water applied (Kirda, 2000).

However, this approach requires precise knowledge of crop

response to water as drought tolerance varies considerably by

species, cultivar and stage of growth.

xxii

1.2. Statement of the problem

Though the study area is endowed with high potential for

production of onion, irrigation water application efficiency is

still undermined. The concept of ‘more crop per drop’ seemed to

be forsaken. Just like the observation made by Mintesinot (2002)

in Tigray, farmers around the study area do not use proper

irrigation scheduling. Ofcourse, farmers in the woreda have

established irrigation frequencies for their crop when

irrigation water is in surplus and in scarce. However, the

frequencies are adjusted regardless of the crop developmental

stages; depending only on the availability of irrigation water.

Though, the water stress during certain growth stages may have

more effect on bulb yield than similar stress at other growth

stages. When water deficit occurs during a specific crop

development period, the yield response can vary depending on the

sensitivity of the crop development stage (Mountannet, 2000).

Moreover, the amount of irrigation water application is

unquantified. It depends on the farmers’ judgment. Once the

xxiii

irrigation is on they stop irrigation when the field is too wet,

an approach that runs counter to conservation of limited

resources. Farmers especially at the upper stream apply as much

water and stop irrigating when they believe the field is well

watered. It is said that the field is well watered when there is

accumulated water over the surface (Fig.2.1). On the other hand,

when water is scares, the limited supply of water along with

large demand of farmers to produce more crops on new irrigable

land even becomes source of dispute. In this case, farmers

usually limit the area allotted for onion production due to the

decreased supply of irrigation water. In addition, the increase

in population in the area is expected to increase total demand

for crop production under irrigation in the coming years.

Increasing crop production and productivity with limited water

and low water use efficiency will be a great challenge.

Improving the available water productivity is therefore the most

important issue needing to be actively addressed for now

(Mintesinot et al, 2004).

Use of deficit irrigation is one of water management approaches

which can save water and at the same time maintain crop yield

xxiv

(Kirda, 2000). Such technique can help these farmers to increase

crop (onion) production per unit of irrigation water. It can

lead to considerable water savings and to a more rational

planning of water distribution (FAO, 2002). The saved water can

bring new areas under irrigation. The increase in additional

irrigated land insures food security due to the increase in

sustainable food production. At the same time, the wise use of

this finite, vulnerable resource will enable us to respond

effectively to new emerging challenges such as climate change

and assure that future generations have enough water. However,

there is a gap of knowledge on how much water at what stage to

irrigate and which stage is more sensitive for water stress.

Enough research was not conducted on this aspect in the area.

This research was then initiated to study the response of bulb

yield of onion to deficit irrigation scheduling, and the

susceptible stage of the crop for the water deficit. The

experiment would have its own share in investigating the

productivity of water in relation to deficit irrigation with

particular emphasis to onion.

xxv

1.3. Objectives of the study

General objective

The general objective of the research was to investigate

the response of onion to different amounts of irrigation

water application under furrow irrigation in Antsokia Gemza

Woreda.

Specific objectives

The specific objectives of the research were:

to identify the susceptible developmental stages of onion

for water stress,

to estimate the crop water productivity of onion under

deficit irrigation practice and

to examine the interaction between irrigation amount and

growth stages of onion.

1.4. Hypothesis

xxvii

Use of deficit irrigation scheduling for onion can increase

the productivity of water without substantial yield

reduction.

xxviii

Chapter 2. Literature Review

2.1.Onion production overview

2.1.1. Agronomic characteristics of onion

Onion (Allium cepa L.) (2n=16) is a biennial herb belongs to the

order Amaryllidales, family Alliacae, subfamily Allilideae and the tribe

Allieae (Currah and Proctor, 1990). The cultivated species of

Allium are native to central and south western Asia, including

Iran, Afghanistan and southwest China (Muhammad, 2004). It is

believed to be one of the first vegetables domesticated by

humans for food and medicine that its seeds have been found in

Egyptian tombs dated to 3200 BC (Rademaker, 2009).

Onion is naturally packaged vegetable consisting of fleshy,

concentric scales that are enclosed in paper like wrapping

leaves, connected at the base by flatted stem disc. The green

leaves above the bulbs are hallowed and rise at the base of the

bulb (Currah and Proctor, 1990). The pseudo-stem which is below

xxix

soil level is flattened to form a disc at the base of the plant.

At the top centre of the stem disc is the shoot apex, from which

leaves are initiated oppositely and alternately so that the

leaves emerge in to ranks at 180 degrees to each other. The

onion root system is fibrous; spreading just beneath the soil

surface with few laterals and total root growth is spare and not

especially aggressive (AVRDC, 2001). It can be propagated by

seeds and bulbs. However, the former is the most widely used by

farmers.

There are more than 750 species within the genus Allium

(Rabinowitch and Currah, 2002). It includes various economically

important cultivated species including the bulb onion (A. cepa),

chive (A. schoenoprasum), garlic (A. sativum), and leek (A. orrum).

They differ in skin color (white, brown, yellow, red, or

purple), size (2.5-15.2cm in diameter), shape (glob-shaped,

flattened or spindle-shaped), pungency and sweetness (Currah and

Proctor, 1990). The most common way of classifying onion

cultivars is by their day length sensitivity as short day (12 to

13 hours threshold), intermediate day (13.5 to 14.5 hours

threshold) and long day (over 14.5 hours threshold) onions

xxx

(Boyhan et al., 2001). However, the bulb onion (A. cepa) is the

most economically valuable species (David et al, 2006). Its

production cycle is quit complex involving vegetative growth,

bulb formation, bulb dormancy and sprouting, flowering and seed

production. Rates of development and growth within each phase

are strongly influenced by environmental conditions and cultural

practices (Brewster, 2008).

2.1.2. Economic significance of onion production

Onion (Allium cepa L.) is an important bulbous crop widely

cultivated throughout the world for its edible bulb and leaves

and plays a key role in the economies of many developing

countries (Boyan et al., 2001). As a staple, onions, including

shallots, garlic and leek, contribute to the food security of

millions of people in most of the developing world (Boyhan, et al.,

2001), and when traded in local markets, they provide income and

employment to rural populations. As an export commodity, onions

are key contributors to the economies of many low-income

countries like Ethiopia. In Ethiopia onion is widely produced

by small scale farmers and commercial growers for local use and

xxxi

export market. Per capita consumption for shallot and onion

together is said to be 1.7 kg in rural areas and 5 kg in towns

as both crops are found mixed in production, marketing and

consumption in Ethiopia (Currah and Proctor, 1990). In the last

few years, the demand for onion has increased due to its high

dry bulb, seed and flower production potential. Dry bulb and

cut flower production for local and export market have shown a

significant increase (Lemma and Shimelis, 2003). According to

World Bank (2004) report in the year 2001 the crop shared one

fourth of the vegetable export quantities and stood third

following green beans and peas contributing about 20% of the

total vegetable export value which was about 244,000 US dollar

of export earnings. In addition to dry bulb, onion cut flower

also constitutes significant proportion of foreign export values

(World Bank, 2004). In between the years 1999-2001 alone, about

1.75 million birr worth cut flower stems were exported. This

indicates that Ethiopia has high potential to benefit from onion

production. In recent years the demand for onion increased for

its high bulb yield, seed and flower production potential. The

establishment of state owned enterprises contributed

xxxii

substantially to the increase in the production and expansion of

area under onion in the country (Lemma and Shimelis, 2003).

Onion, shallot and garlic are major crops in many tropical

countries being valued for their flavor, nutritive and medicinal

value. The demand for them is world-wide. Onions are grown for a

variety of purposes, as fresh shoots for green 'salad' onions,

and as bulbs for: flavoring varieties of dishes, saucers, soup,

sandwiches, pickling and used as flavoring compounds in food

processing industries. It is characterized by the remarkable

sulfur-containing volatile oil (allyl propyl disulphide)

compounds they contain, which give them their distinctive smell

and pungency (Brewster, 2008). These substances has been

extensively used as precursor of the flavor compounds in food

processing industries and used as a medicine to cure a wide

range of aliments. In a traditional medicine garlic and onion

have been used in the prevention and treatment of

atherosclerosis, coronary heart disease, in reducing blood

cholesterol level, in the treatments of diabetes, cancer and

asthma (Brewster, 2008). The mature bulb contains some starch,

appreciable quantities of sugars, some protein, and vitamins A,

B and C (Decoteau, 2000).

xxxiii

2.1.3. Onion production in Ethiopia

As a result of the increase in both the surface area cultivated

and the yield obtained, the world production of onions is now

above 57884000 Mt per year which is by far higher than the

14,164,000 Mt per year obtained in 1960 (FAO, 2007). The average

world yields increased from 12 t ha−1 in the early 1960s to 18 t

ha−1 in 2005, while the productivity of tropical onion is around

9.6 t ha,-1 which is very low (FAO, 2007). Tropical countries,

having about 45% of the world’s arable land, grow about 35% of

the world’s onions (Pathak, 1994). The African average bulb

yield were 12.3 t ha-1. This figure is still very far from the 54

t ha−1 yielded on average in Korea Republic, USA and the EU

countries.

Onion is a recently introduced bulb crop in agricultural

community of Ethiopia and is rapidly becoming popular among

producers and consumers (Geremew et al., 2010). Currently, onion

production is rapidly expanding in all administrative regions of

Ethiopia where there are favorable climate and soil types either

in small pockets or large commercial farms (MARC, 2003). Onion

xxxiv

is becoming one of the most important vegetable crops grown in

the country, where the bulk is produced in traditional

agricultural system. It has comparative advantage over its close

alley shallot in that it is high yielder, can easily be

propagated through seed and both its bulbs and flowers have got

export values (Lemma and Shimelis, 2003).

Onions are produced in the country on an estimated area of about

18,000 hectares of which 3 % was in the state sector and the

rest under traditional farming system (MARC, 2003). In Amhara

region, root and bulb crops covered about 0.7 % of the regional

crop area and 4.3% of the production volume. Onion shared 11 %

(3684 ha) of the regional root and bulb crops area and added

about 14% (40848.4 tones) to the regional volume of root and

bulb crops production (CSA, 2009). The most popular onion

cultivars include Adama red, Bombay red, Melkam, and Red creole.

The first two cultivars are widely popularized and extensively

produced in many regions of the country (MARC, 2003). The

average yield in Ethiopia is approximately 10.2 ton ha-1 compare

to over 30 ton ha-1 in other countries (Korean Republic, 62.5t

ha-1), (USA, 51.1t ha-1), (Ireland, 55.9 t ha-1) (FAO, 2007).

xxxv

However, experimental yields obtained from Bombey red variety so

far ranged from 30 to 40 t ha-1 in the Awash valley (Lemma and

Herath, 1994; Lemma and Shimels, 2003).

2.1.4. Optimum growth environments of onion

Depending on the season of the year and type of cultivar, it can

grow well all year round at 500m to 2400 meter above sea level

with optimum range of 700-1800 meters above sea level. It was

reported that onion grows in all types of soils from sandy loam

to heavy clay. Highest yield was attained from freely drained

friable loam soil with pH of 6.5 to 7 (Lemma and Shimelis, 2003;

Tindall, 1983). According to Tindall (1983) relatively high

levels of organic mater are required for optimum growth and

development. In addition, adequate reserves of the major

elements, particularly nitrogen and potash, should be available

throughout the growing period. Temperature is also an important

environmental factor that affects onion bulb development and

production. Optimum temperature for plant development is between

13 and 24 0C, although the range for seedling growth is narrow,

20-25 0C. High temperature favors bulbing and curing.

xxxvi

Temperature of 18.3-240C day and 10-12 0C nights are ideal for

bulb production in Ethiopia (MARC, 2003).

Moisture is one of the most vital environmental factors that

affect onion production. Its growth rate can be inhibited well

before the leaves wilt visibly even when the roots seem

adequately supplied with water (Drinkwater and Janes, 1955).

Ronald et al. (1999) indicated that onion plant’s rate of

transpiration, photosynthesis and growth are reduced even by

mild water stress. Unlike many plants, onions show little

capacity to reduce their leaf water potential by osmotic

adjustment to compensate for reduced availability of water at

the root whether caused by salinity or by drying of the soil

(Ronald et al., 1999). The shallow root depth of onion makes it to

be particularly sensitive for moisture stress at the time of

bulbing (Brewster, 2008). According to Drinkwater and Janes

(1955), 100% of the water uptake occurs in the first 30 to 50 cm

soil depth. Under an evaporation rate of 5 to 6 mm day-1 the rate

of water uptake starts to reduce when about 25 percent of the

total available soil water (P = 0.25) has been depleted

(Doorenbos et al., 1979). Both shallot and garlic are produced

xxxvii

under rain-fed whereas, onion is produced mainly under

irrigation. Otherwise, incidence of disease may cause a

considerable reduction in rainy season (Jackson et al., 1985).

2.2.Irrigation development and management

2.2.1. Irrigation development

There is indisputable evidence that irrigating land leads to

increased productivity. Irrigation was a necessary input into

the high yield varieties developed during the Green Revolution.

One acre of irrigated cropland is worth multiple acres of rain-

fed cropland. Between 1962 and 1996, the irrigated area in

developing countries increased at about 2% a year, leading to a

near doubling in irrigated land (Zilberman and Schoengold(nd)).

For example, in 1950 India had an irrigation potential of 22.6

mha. By 1993-94 this had grown to 86 million ha (Saleth, 1996).

Between 1949 and 1998, the amount of land in China under

irrigation increased from 16 mha to 52.3 mha. This represented a

change from 16% to 40% of China’s total farmland (Zilberman and

Schoengold(nd) cited Guangzhi and Hansong, (1999)). Irrigation

has increased not only the amount of land under cultivation, but

xxxviii

also the yields on existing cropland. For instance, in Asia

yields from most crops have increased 100-400% after irrigation

(FAO, 1996). It allows farmers to apply water at the most

beneficial times for the crop, instead of being subject to the

timing of rainfall. FAO (1997) estimate indicated that irrigated

agriculture produces nearly 40 % of food and agriculture

commodities on 17% of agricultural land, in which 75% of all

irrigated land is in developing countries. In Africa about 12.2

million hectares benefit from irrigation which is equal to only

about 8.5% of the cultivated land and in sub-Saharan Africa only

about 10% of the agricultural production comes from irrigated

land (FAO, 1997).

Irrigation is practiced in Ethiopia since ancient times

producing subsistence food crops. Traditional irrigation has

been practiced for more than a century in North Shewa, Gojam,

and Harar, too (ARARI, 2008). However, modern irrigation systems

were started in the 1960s with the objective of producing

industrial crops in Awash Valley (Sileshi et al., 2007). Private

concessionaires who operated farms for growing commercial crops

such as cotton, sugarcane and horticultural crops started the

xxxix

first formal irrigation schemes in the late 1950s in the upper

and lower Awash Valley. In the 1960s, irrigated agriculture was

expanded in all parts of the Awash Valley and in the Lower Rift

Valley due to the water regulation afforded by the construction

of the Koka dam and reservoir that regulated flows with benefits

of flood control, hydropower and assured irrigation water supply

(Sileshi et al., 2007). However, it is only in the after math of

the 1984 drought which has had a devastating effect on the lives

of thousands of people that the government was induced to turn

its attention towards irrigation as a possible solution to help

victimized farmers (Getaneh, 2002). In the 1980s with the

recurring cycle of drought and environmental hazards, the need

for small scale irrigation development expanded to other parts

of the country to address drought and food shortages, and the

need for more food for the internal market.

Currently, the government is giving more emphasis to the sub-

sector as a means of enhancing the food security situation in

the country. The total area under irrigation in 2006 was

reported to be 603,359 hectares, of which traditional irrigation

accounts for 479,049 hectares while 124,569 hectares of land was

xl

developed through medium and large scale irrigation schemes

(MoFED, 2007). Amhara region is one of the regional states of

the country that emphasizing on developing irrigation-based

agriculture to attain food security at household and state

level. It has more than 700,000 ha of potentially irrigable

land. Despite this huge potential of irrigable land only 90,000

ha of land or about 12 % of the irrigable land is currently

under irrigation (Sileshi et al., 2007), out of which traditional

irrigation accounts 70,000 hectares (85%) of the total irrigable

land (Enyew, 2007). Although few irrigation schemes were

established recently, most traditional schemes in North Shewa

Zone (in which Antsokia Gemza woreda is found) were established

long ago that farmers were observed to have difficulties

remembering when they were operational (Yonas et al, 2008).

In Antsokia Gemza woreda most traditional schemes are

constructed based on run-of-river diversion of streams and

springs. These schemes are built under sprout from farmers own

initiative with government technical and material support. It is

managed and controlled by the users. Traditional water

committees, locally known as ‘water fathers’, administer the

xli

water distribution and coordinate the maintenance activities of

the schemes. The modern small-scale irrigation schemes were

built from 1995 – 2003 (WVE, 2009) by World Vision Ethiopia

(WVE) Antsokia Gemza area development program with direct farmer

participation. (The irrigation schemes constructed by WVE

Antsokia Gemza area development program are presented in

appendix B, Table B.4.). In such schemes, efforts are being made

to involve farmers progressively in various aspects of

management of small-scale irrigation systems starting from

planning, implementation and management aspects, particularly in

water distribution and operation and maintenance. There are also

water user associations which handle water allocation,

operation, and other maintenance functions. This can pave the

way to introduce new water management techniques like deficit

irrigation in the woreda.

2.2.2. Irrigation scheduling: the tool for water

management

Irrigation scheduling is the process of determining when to

irrigate and how much water to apply per irrigation. It has been

described as the primary tool to improve water use efficiency,

xlii

increase crop yields, increase the availability of water

resources, and provoke a positive effect on the quality of soil

and ground water (FAO, 1996). Timing and depth criteria for

irrigation scheduling can be established by using several

approaches based on soil water measurements, soil water balance

estimates and plant stress indicators, in combination with

simple rules or very sophisticated models. Since crops

irrigation need is decided by the evaporative demand of the

ambient atmosphere, soil water status and plant characteristics,

a thorough understanding of the soil-plant-atmosphere

relationship is essential for proper irrigation scheduling

(Majumdar, 2000). The author indicated that the criteria for

scheduling irrigation as attempted from time to time may be

grouped in to three categories, namely plant criteria, criteria

based on soil water status and meteorological criteria. The

water status of the plant in terms of leaf water potential may

serve as a sound basis for irrigation scheduling. There are also

a wide range of commercially available instruments to measure

soil moisture for irrigation scheduling. These include neutron

probes, tensiometer, and Time Domain Reflectrometer (TDR). The

role of climate in governing the water needs of crops was

xliii

recognized and criteria based on evapotranspiration were

utilized for scheduling irrigation. A range of empirical methods

was developed to estimate potential crop evapotranspiration from

readily available climatic parameters. The water requirement of

a given crop was derived through a crop coefficient that

integrated the combined effects of crop transpiration and soil

evaporation into a single crop coefficient as in eq.1.

Where: ETo is reference crop

evapotranspiration

Kc is crop coefficient

ETc is the crop

evapotranspiration.

ETc is defined as the evapotranspiration from a disease-free,

well fertilized crop, grown in large fields, under optimum soil

water conditions, and achieving full production under the given

ecological environment (Kassam and Smith, 2001; Allen et al., 1998;

Doorenbos et al., 1979). Whereas, ETo is the evapotranspiration

from a reference crop with the specific characteristics of

xliv

grass, fully covering the soil and not short of water and

represents the evaporative demand of the atmosphere at a

specific location and the time of the year independently of crop

type, crop development and management practices, and soil

factors (Doorenbos et al., 1979; Allen et al 1998). The only

factors affecting ETo are climatic parameters. Consequently, ETo

is a climatic parameter and can be computed from weather data.

Crop transpiration is determined by the typical crop

physiological and morphological characteristics and increases

over the growing season with the growth of the canopy surface.

Soil evaporation decreases proportionally over the growing

season as the ground surface is increasingly shaded by the crop

canopy.

The net irrigation requirement is calculated as the depth of

water required to replenish the soil water content to field

capacity in the irrigated crop root zone. Depth of irrigation

application is the depth of water that can be stored within the

root zone between field capacity and the allowable level the

soil water can be depleted for a given crop, soil and climate.

It is equal to the readily available soil water (RAW) over the

xlv

root zone. According to Doorenbos et al. (1979), the total

available water (TAW) for plant use in the root zone is commonly

defined as the range of soil moisture held at a negative

apparent pressure of 0.1 to 0.33 bar (a soil moisture level

(called 'field capacity') and 15 bars (called the 'permanent

wilting point'). The TAW will vary from 250 mm/m for silty loams

to as low as 60 mm/m for sandy soils. Irrigation water is added

to the water balance when the available soil water storage

reduced to RAW (Doorenbos et al., 1979). Readily available water

(RAW) is the fraction of stored water that a crop can extract

from the root zone without suffering stress and is expressed as

the product of stored water and allowable soil water depletion.

Shock et al. (2010) indicated that irrigation scheduling is

directly related to profitable onion production and sustainable

agricultural practices. They demonstrated that onion yield and

grade are very closely related to irrigation practices. Careful

attention to irrigation scheduling can help assure high onion

yields, better bulb storability, and better internal quality.

Small errors in irrigation can result in large losses in yield,

especially in marketable yield of the larger size class bulbs

xlvi

(Shock et al., 2010). The seasonal water requirement of onion

varied according to the climate conditions. Variability in the

water requirements for onions is also a function of location and

irrigation method. According to Lemma and Shimelis (2003), the

crop demands about 400-800 mm per growing season for the

formation of large bulb size and high yield. Whereas, FAO (2002)

reported that its demand vary with climate and 350 to 550mm

water is optimum for bulb production. Depending on climatic and

soil condition Doorenbos et al. (1979) reported that the water

requirements for optimum yield (35 to 45t ha−1) might vary from

35 to 55 cm of water using furrow irrigation. Whereas, Ells et al.

(1993) reported that furrow-irrigated onions required 104 cm of

water to obtain a yield of 59t ha−1.

2.2.2. Farmers experience on irrigation scheduling and

water management in the study area

Traditional small-scale irrigation schemes are the dominant

irrigation water sources in the study area. They are managed by

local water administration body known as ‘Yewuha abat’ which means

‘’father of water’’. Yewuha abat is an elected member of the

xlvii

community whom the farmers agree up on to be in charge of all

water issues. It is well recognized by the kebele’s leaders and

‘limat budin’. Water dispute and other water distribution issues

are solved by the ‘Yewuha abat’. If things get out of the capacity

of this body the kebele administration and elders will join to

solve the problem. Most of the cases however, are handled by the

‘yewuha abat’. While, most of the recently constructed modern

irrigation schemes are managed by water users associations.

There are more than five water users associations in the woreda

which encompass more than 500 beneficiaries in each. Members of

the WUA have annual financial fee for operation and maintenance

of the scheme. In some WUAs, specially when water is scarce,

water is allocated to their members in hour. While in some WUAs,

two or three months before members inform their association

about the type of irrigated crop they plan to grow. Thus, crops

are grown as per the potential of the irrigation scheme and

water is distributed to each member in rotation.

Flood irrigation is widely used method of water application for

crops other than vegetables. Furrow irrigation is used for row

cropped onion and other vegetables. According to the interview,

xlviii

farmers selected these methods due to lower labor requirement

and lack of knowledge about other irrigation methods.

Traditionally water is measured by the size of secondary and

tertiary canals/boy/ which are judged by the size of water it

carries. These measurements are applied to distribute

irrigation water to each farmer. For instance, it was observed

and pointed out by farmers that irrigation water is measured by

’boy wuha’. One ‘boy wuha’ is the same as saying water amount which

satisfy optimum flow in a furrow. Although volumetric discharge

measurement is unknown in the area, proportioning of water gives

an entry point in introducing formal water measurement systems

for economizing the use of the resource.

xlix

Figure 2.1. Accumulated water over the surface of farmers field

due to over irrigation of onion

Farmers in the woreda have established irrigation frequencies

for their crops when water is in surplus and in scares (Table

2.1). Based on the availability of water these frequencies are

adjusted. However, the amount of water application depends on

the farmers’ judgment. They apply to the extent that water is

accumulated over the surface. Farms were observed to be over

irrigated once the supply is on (Fig.2.1). This is related to

the farmers believe that application of more water can bring

more yield.

According to the assessments made on those farmers who have the

experience in irrigation agriculture, commercial fertilizer was

rarely applied for other crops except onion. Even, the use of

fertilizer for onion is below the recommended level (1qt Urea

ha-1). They do not use DAP for vegetable production. This is

mainly because of fertilizer prices and for fear of water

shortages which might result in crop burns by fertilizer. This

indicates that there is a need to improve the traditional

schemes in terms of water productivity.

l

Table 2.1. Irrigation frequencies in some of the assessed

kebeles

Kebele Scheme

Name

Irrigate

d crop

Frequency of irrigation

During

sufficient

water

During scarce

water

Agla

Majatte

Lay Jara Onion 4-5 days 8-9days

Tomato 2-3

times/season

2-3

times/season

teff Twice/season Once/season

Agla

Majette

Tach

Jara

Onion 6 days 9 days

Tomato 15days 20 days

teff 3-4

times/season

Twice/season

Mekoy 03 Gudaber Onion 8 days days

interval

13 days

Sweet

potato

Once a month Once a season

teff 7 days

interval

15-30 days

Fruit

trees

10 days >20days

Kobekob Sirinka Pepper 15days 25 days

interval

Onion 4-5days 8days

interval

Maize 9 days 11-15days

lii

Tomato 8days 15days

2.2.3. Concepts of deficit irrigation

Rapid increases in the world's population have made the

efficient use of irrigation water vitally important,

particularly in poorer countries, where the greatest potential

for increasing food production and rural incomes is often to be

found in irrigated areas. There is increased need to maximize

the productivity of both land and water. ’Inputs’ to land may

improve land productivity but inputs to water may not change the

productive capacity of water. Improving ‘water security’ and

‘crop water productivity (CWP)’ can, however, result in higher

productivity (Mintesinot et al., 2004). Water security, in this

context is used to signify the all year round availability of

water for production purposes. CWP is a term commonly used to

describe the relationship between water and agricultural

product. Therefore, CWP can be defined as the relationship

between units produced and volume of irrigation water applied

and is estimated by dividing crop yield by total applied water

liii

(Samson and Ketema, 2003; Yenesew and Tilahun, 2009; Heping,

2003; Biswas et al., 2003; Urea et al., 2003; Steduto, 1996).

In Ethiopia, the issue of ‘water security’ is being addressed

through the implementations of water harvesting projects. Under

these projects many efforts have been done to construct and

develop river diversion, ponds, earth dams, flood spreading and

spring development. The issue of CWP, however, is little

considered. Promoting productivity, therefore, is an urgent

necessity. One of the strategies to increases CWP is the use of

deficit irrigation (Zwart and Bastiaanssen, 2004).

Deficit irrigation was developed to control vegetative vigor in

high density orchards in order to optimize fruit size, fruit

fullness and fruit quality (Goodwin and Boland, 2000). It is the

practice of using irrigation to maintain plant water status

within the prescribed limits of deficit with respect to maximum

water potential with a prescribed part or parts of the seasonal

cycle of plant development (Shaozong, 2004). Similarly, Shock

and Feibert (2006) stated that deficit irrigation is a strategy

liv

that allows a crop to sustain some degree of water deficit in

order to reduce irrigation costs and potentially increase

revenue. Its objective is to save water by subjecting crops to

periods of moisture stress with minimal effect of yields (Smith

et al., 2000).

According to Shaozong (2004) the potential benefits of deficit

irrigation derive from three factors: increasing irrigation

efficiency, reducing cost of irrigation and opportunity costs of

water, and improving quality and/or yield. Therefore, it is

important to mitigate drastic yield reductions (Bazza and Tayya,

1999) and can maximize water productivity for higher yields per

unit of irrigation water applied (Kirda, 2000). However, when

the water stress is sever or occurs at the critical growth

stages of crops, deficit irrigation may only lead to drastic

reduction in crop yield and a negative impact on productivity of

water and economic return (Henry et al., 2004).

Oweis et al. (1999) suggested that economically reasonable yields

could be obtained with deficit irrigation when the dose and

interval of irrigation are well monitored. They noted that

lv

deficit irrigation requires more control over the amount and

timing of water application than full irrigation. They conclude

that with established crop water production functions and

sensitive stages of crop growth to water stress, optimal deficit

irrigation could be scheduled with minimum yield reduction

compared with full irrigation.

On the other hand, properly practiced deficit irrigation may

increase crop quality. For instance, the protein content and

baking quality of wheat, the length and strength of cotton

fibers, and the sucrose concentration of sugar beet and grape

have been reported by the above author to increase under deficit

irrigation. In addition, the established crop production

functions made it possible to solve the problem of allocation of

limited water resources between crops where there is competition

for limited available water in dry areas. It is practiced in

many arid areas of the world, and increase demand on water

supplied worldwide suggested the practice must be increase

(Shani and Dudley, 2001).

lvi

2.2.4.1. Influence of deficit irrigation on yield and

yield components

Water is essential for plant growth, and it is needed in much

larger quantities than are the nutrients (Teixeira et al., 2003).

The author mentioned that water is essential and as an

inevitable consequence of opening their stomata to ensure

gaseous exchange during photosynthesis. During the period of

water stress they react by closing their stomata to minimize

water loss through transpiration. This has an impact on gas

exchange with in the leaf and results to slow down

photosynthesis and growth (Allen et al., 1998; Brewster, 2008).

The stress will be aggravated and the effect of closure of

stomata is more impose an effect when there is salinity problem

(Brewster and Rabinowitch, 1990).

Sadeghipour (2008) indicated that vaying timing of irrigation

had significant effect on yield and yield conponenets of

Mungbean (Vigna radiate L. Wilczek) varieties. Stress that occurred

at the reproductive stages affect seed yield more sevierly than

its occurrence on other stages. The author obtained that stress

lvii

at flowering stage reduce number of pods per plant, number of

seed per pod and seed yield, while, withholding irrigation at

pod filling stage decreased 1000 seed weight. Another study on

soybean by Stegman et al. (1990) showed that although short term

stress during early flowering resulted in flower and pod drop in

the lower canopy, increased pod set in the upper nods compensate

for this where is a resumption of normal irrigation.

In two years study on wheat, increasing irrigation resulted in

progressively higher leaf area index, increased crop growth

rate, and increased above ground biomass (Pandy et al., 2001). The

same author explained that deficit water supply in the earlier

growth stage of wheat can result in sufficient above ground

biomass to support an economically acceptable yield. However,

the adverse effects of water stress on crop growth rate can lead

to reduced biomass yield. Asseng et al. (1998) indicated that root

growth of wheat slowed in the upper layers, but compensatory

growth occurred in deeper layers during drying. Root growth was

greatest in the upper layers, immediately after rewetting, water

uptake rate increased quickly after rewetting, and exceeded the

uptake rate of the non stressed treatment about 2-3 weeks after

lviii

the deficit is released. Rosenthal et al. (1987) also indicated

that the effect of pre and post anthesis water deficit on

transpiration of wheat were not significantly different (p <

0.05). The same author studied on cotton and sorghum and found

that water deficits below 20% to 30% plant available water

reduced transpiration and enhanced leaf senescence.

Yenesew and Tilahun (2009) indicated the significant impact of

variation in level (amount) of irrigation water application on

grain yield of maize. They explained that, in the case of stress

by 75% deficit at a specific stage, the effect of stress was

severe during the mid season stage. On the other hand, water

deficit during the early and maturity stage had a limited effect

on yield. Stressing the crop by 75% deficit throughout the

growing season resulted in the highest yield reduction.

Smith et al. (2000) reported that water stress imposed during

establishment, flowering and tuber formation developmental

stages of potato has caused yield reduction compared to full

irrigation. The measured yield reductions and the simulation

lix

results revealed particular sensitivity to moisture stress

during establishment and flowering stages.

Several studies have been conducted on limited irrigation water

application and its effect on bulb yield of onion by imposing

soil water stress at some phonological stages during the growing

period (Kadayifcia et al., 2005 cited Shock et al., 1998; Shock et

al., 2000; Singh and Alderfer, 1996; Van Eeden and Myburgh, 1971;

Mart´ın de Santa Olalla et al., 2004). These studies gave clear

proof that the bulb and dry matter production were highly

dependent on appropriate water supply. Singh and Alderfer (1996)

reported that soil water stress at any developmental stage of

onion can leads to reduction in marketable yield. They further

observed that with regard to yield reduction, onions are more

sensitive to water stress during bulb formation and enlargement

than during the vegetative stage. Dragland (1974) also reported

that three weeks long water stressed onion in the early

development stage reduce onion yield more than when the imposed

near the end of the growing season. In line with this, Van Eeden

and Myburgh (1971) reported that water stress imposed late in

the season reduced onion total yield by 15% when compared to the

lx

yield with no water stress. Onion is considered a shallow rooted

crop and is comparatively sensitive to water stress. Drinkwater

and Janes (1955) noted that the growth of onion can be inhibited

well before the leaves wilt visibly even when the roots seem

adequately supplied with water.

According to Lemma and Shimelis (2003), dry bulb yield decline

from 20.4 to 11t ha-1 as irrigation interval increased from three

to twelve days, while yield increment was observed from 12.9 to

17t ha-1 as the amount of water applied increased from 3-7cm

depth. The same author obtained in sandy loam soil that, 5cm

water applied at 3-6 days interval gave the highest yield of 17-

20.4t ha-1.

Shock et al. (2003) reported that water stress at the four-leaf

and at the six-leaf stages of onion resulted in fewer single-

centered onions than the unstressed check. Water stress at the

later stages did not affect onion single-centeredness. Water

stress did not affect translucent scale. In contrast to Hegde

(1986), the short-duration water stress in this trial did not

affect onion yield or grade. Another experiment on the effect of

lxi

irrigation regime on growth and yield of onion showed an

improvement on plant growth with increasing the amounts of

irrigation water. Increasing total water application from 762 to

2381 and 857 to 2095 mm resulted in total yield increases of 70%

and 37.6% in the first and second seasons, respectively. Average

bulb weight, length and diameter were significantly increased at

higher levels of irrigation water (Al-Harbi, 2002). These

results seemed to be in a close agreement with those reported by

Shock et al. (2003). He reported that total yield and marketable

yields increased with increasing irrigation threshold. The

improvements of total yield response to high amounts of total

water application could be attributed to the enhancing effects

of water to crop’s biological functions and growth in addition

to the improving effects of water on nutrients availability.

Kumar et al. (2007), Orta and Ener (2001) and Faten et al. (2010)

reported the significant effect of irrigation amount on growth

parameters and yield of onion. There have been also several

reports on the effects of irrigation on onion bulb yield and

their subsequent storage life (Gomie et al., 2000). According to

Kumar et al. (2007) the best yield was recorded from the highest

lxii

irrigation amount (1.2% of cumulative pan evaporation)

associated with the higher percentage of bulbs having diameter

greater than 45 mm. In line with this Biswas et al. (2010) also

indicated that bulb yield of onion showed significant variation

among treatments. The yield of bulb increased almost linearly

with increasing number of irrigation. Faten et al. (2010) found

reduction of onion plant growth by both medium and longer

irrigation intervals. Whereas, the superiority of onion plants

which were irrigated at the short interval, i.e. 14 days might

be attributed to that, water is one of the main raw materials

for photosynthesis and required for translocation of nutrients

from roots media to different plant organs.

2.2.4.2. Influence of deficit irrigation on crop water

productivity

Water is the major constitute of living plant tissues which

accounts for about 90% and many physiological processes depend

on it. However, only a very small part about 1% of water needed

by a plant is used in metabolic process and the rest is lost

through transpiration (Kumar et al., 2007). In most areas water

resources are being over exploited for full irrigation, while

lxiii

sustainable water use can be obtained only by producing more

crops from less water. Crop water productivity can be maximized

when water is conserved and maximal crop growth is promoted. The

former requires minimizing loses through run off, seepage and

evaporation. The later task includes improved agronomic

practices and use of high yielding varieties. English and Raja

(1996) reported that deficit irrigation averaging 64% of full

irrigation was found to be economically equivalent to full

irrigation when water was the limiting factor. According to

Henry et al. (2004), irrigation scheduling protocol which entails

a 14 day irrigation interval at crop vegetative developmental

stage gave the best productivity of water in terms of water

applied being 0.5 kg/m3 than regular irrigation carried out at

7 day interval (0.44kg/m3). The crop yield based on such

scheduling was not significantly different. Another study showed

that two third of full irrigation increased productivity of

total applied water by 19-28% for maize. The risk with deficit

irrigation was low because the response curve of crop yield to

water supply often has a wide plateau; considerable amount of

water can be saved without a significant yield reduction

compared with full irrigation (Heping, 2003).

lxiv

Harmoniously with the above result, Yenesew and Tilahun (2009)

indicated that the water productivity of maize was the lowest

(1.72 kg/m3) at optimum irrigation water application and the

highest (2.96 kg/m3) at stress of 75% deficit throughout the

growth season. They noted that, although at individual farmer’s

level, maximum yield is obtained when the entire crop water

requirement is fulfilled, practicing deficit irrigation could

increase the irrigated area as a result of high crop water

productivity. The same author concluded that strategy of

stressing maize by one-half at the beginning and end of season

and using the water to irrigate a greater area, results in

higher aggregate production than providing optimum irrigation

throughout the season for a smaller area.

In contrast to Yenesew and Tilahun (2009), Payero et al. ( 2006)

suggest that increase crop water productivity by imposing

deficit irrigation for maize might not be a beneficial strategy

as the CWP linearly increased with evapotranspiration (R2 =

0.75). However, it is recognized that there could be other good

justifications for deficit irrigation other than increasing CWP.

lxv

For instance, Zwart and Bastiaanssen (2004) reviewed measured

CWP for several crops around the world and concluded that the

CWP could be significantly increased if irrigation was reduced

and crop water deficit was intentionally induced.

Salkini and Oweis (1993) found that supplementing only 50% of

the rain fed crop irrigation requirements reduce crop yield by

only 10-20% relative to full irrigation. Using the saved 50 % to

irrigate an equal area gives a much greater return in the total

production. Irrigation scheduling to manage supplemental water

for maximum net profit of winter wheat in the Northern china

showed that a single irrigation in wet years, two irrigations in

normal years and three in dry years produce maximum profit

(Heping, 2003). In comparison to productivity of water in fully

irrigated areas (when rainfall effect is negligible), the

productivity is higher with supplemental irrigation. In full

irrigated areas with good management, wheat grain yield is about

6t ha-1 using 800mm of water. Thus, the water productivity is

about 0.75kg m-3, one third of that under supplemental irrigation

with similar management (Salkini and Oweis, 1993).

lxvi

Experiment during the rainy season done on onion in Bangladesh

showed that the highest crop water productivity (36.44kg/mm) was

obtained in the treatments with four irrigations at 15 days

interval with a total water use of 239mm. However; the total

water use of onion (two years average) during the rainy season

was the highest (279.5mm) in treatment with six irrigations at

10 days interval (Biswas et al., 2003). Al-Harbi (2002) noticed

that water productivity of onion was increased with increasing

the amounts of applied water. Urrea et al. (2003) found the

greatest water productivity in garlic by application of deficit

irrigation at the bulbification stage. Oda et al. (2010) found the

highest CWP under irrigation with 80% of full irrigation for

three growing seasons. Similar results were obtained by Samson

and Ketema (2007) who stated that deficit irrigation application

for onion increased CWP. In line with this Kumar et al. (2007)

indicated that CWP of onion was the highest in application of

irrigation water amount equivalent to 0.8% of the cumulative pan

evaporation and then declined with the increase in irrigation

water amount.

lxvii

Samson and Ketema (2007) reported that all deficit irrigation

water applications increased the CWP of onion from a minimum of

6% (application of 25% of Etc at initial stage) to a maximum of

13% by applying irrigation water 75% of Etc throughout the whole

growing season compared to the optimum application. They

concluded that increasing the irrigated area with the saved

water would compensate for any yield loss. The average water

utilization efficiency for harvested yield of bulb, that

containing 85 to 90% moisture is 8-10 kgm-3 (FAO, 2002).

Chapter 3. Materials and methods

3.1. Description of the study area

3.1.1. Location

The experiment was conducted in Antsokia Gemza Woreda in North

Eastern part of Ethiopia at a distance of 350kms NE of Addis

Ababa (Fig.3.1). It is one of the rural woreda of Eastern Amhara

in the Amhara National regional state located at 10o37’ N

latitude and 39o52’ longitude, at an altitude of 1400-2800

meters above sea level. The woreda has a total area of

lxviii

386.10km2 (CSA, 1999) and lies on the watershed of Borkena river.

Regarding topography of the woreda 46% is mountainous, 11% is

terrain and 43% is plateaus (AGWARDO, 2010).

Figure 3.1. Location of the experimental site

lxix

Ants

okia

Gem

za

wore

daAmha

ra r

egio

n

Ethi

opi

aNo

rth

shoa

zo

ne

Experimental siteMajettie (town)Area of land irrigated by Jara river schemeMekoy (town)

0 5 10

3.1.2. Climate

The area has three agro ecological zones of low, mid, and

highlands, out of which 45% is lowland, 44% is midland and 11%

is highland (AGWARDO, 2010). Its mean annual temperature is

20.1oC with a mean annual maximum and minimum temperature of

28.62oC and 14oC, respectively. The mean annual rainfall at the

study area is 1074mm with a bimodal precipitation of 800-1200mm

rainfall in which more than 60% of the rainfall is obtained in

July, August and September (Fig.3.2). The long term climatic

data of the area is presented in appendix A.

lxx

Ave

rage

RF

(mm)

&

RH (

%)

Figure 3.2 Mean monthly rainfalls (mm), maximum and minimum

temperature (oC) and relative humidity (%) of the study area.

3.1.3. Soil

There is little information about biological and physico-

chemical properties of the soil around the area. However, the

extensive plain of the woreda that is lying below the highland

is rich in alluvial soil (Tibebe and Siobhan, 2000) typically

used for vegetable and other crop production. According to

AGWARDO (2010), the dominant soil around the woreda is sandy

loam soil. The lab result of some physico-chemical properties

of the soil is presented in section 3.3.1.

lxxi

3.1.4. Farming system

About 90% of the people practice mixed agriculture as a means of

livelihood. According to AGWARDO (2010), the land use pattern of

the woreda is 47% cultivated, 20% uncultivated and less than 3%

is grazing land. About 30% of the land is covered with bush

grassland and wasteland too. The major crops cultivated in the

area are cereals: sorghum, teff, maize, barley and wheat; pulses:

beans and peas; fruits: citrus, mango, avocado and papaya;

vegetables: onion, tomato, cabbages, and potato. The crops

cultivated in irrigation in 2009 cropping season in the order of

area coverage are maize (34.84%), onion (28.22%) and teff (4.6%)

and their respective total yield was 5106.2, 37848.3 and 331.6

tons (Table 3.1). People also have domestic animals like cattle,

sheep, goat, and pack animals. Planting date varies according to

the crop type and availability of moisture. If there is enough

moisture, starting from half June crops like wheat barely and

beans have been sown, while sorghum and maize have been sown in

April. In the woreda onion crop production as rain fed crop is

not common because of high disease incidence in rainy season. It

is extensively produced in irrigation during the off season.

lxxii

Recently, cropping pattern in traditional irrigating areas of

the woreda is changing. For example, long season sorghum planted

in late April is replaced by irrigated onion and other vegetable

crops. These changes are mainly due the increased need of

farmers to irrigated agriculture along with the introduction of

high valued crops like onion, driven by the market.

Irrigated agriculture has been practiced for a long time in the

woreda using different irrigation schemes like river diversions,

springs, hand dug wells etc. The majority of farmers grow

vegetables and crops twice a year; one during the dry season

(from January to May) with irrigation and the second during the

main rainy season (from July to September) with or without

supplemental irrigation. There are also farmers who are

producing crops twice in the dry season using irrigation and

once in the wet season. According to AGWARDO (2010) annual

report, the number of these farmers is increasing from time to

time. It rose from 73 in 2006 to 14203 in 2009. The cultivated

area also rose from 16.39 ha in 2006 to 2915 ha in 2009. These

farmers produce their first crop from the beginning of October

to February and the second crop has been planted at the end of

lxxiii

February and reaches to harvest before the beginning of the main

rainy season. In the main rainy season early maturing crops like

teff, mung bean, early maturing variety of maize and some

vegetables are grown. The total area irrigated by each

irrigation scheme during 2008 and 2009 is presented in table

3.2.

Table 3.1 Average yields (t) and area coverage (ha) for the major irrigated crops (AGWARDO, 2010).

Type of Cultivated area (ha) Yield per cultivated area

(ton)

Crops

grown

2006 2007 2008 2009 2006 2007 2008 2009

Teff 40.75 110.9 223 178.6 52.3 105.4 162.5 331.6

Maize 1037.

6

1275 1355.

2

1342 2751.

7

3071.

5

3132.

5

5106.

2

Onion 675 796.4 1086.

9

1251.

9

3314.

2

6512.

5

19275

.4

37848

.3

Tomato 146.9 78.8 46.88 132.4 2209.

8

2942.

7

2809.

1

5012.

6

Cabbage 12.76 17.5 23.3 40.2 624.9 525.0 1009.

8

1952.

5

lxxiv

S/potato 63.6 28.9 74.5 140.1 902.8 352.8 1080.

7

2509.

3

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.Total 3038.

5

3202.

5

3557.

7

3851.

8

10463

.9

16608

.1

42619

.3

72171

.9

Table 3.2. Types of irrigation scheme and their respective

irrigated area (ha) in 2008 and 2009 cropping seasons (AGWARDO,

2010)

Product

ion

Year

Types of irrigation scheme

Earth

dam

Modern

diversi

on

Traditio

nal

diversio

n

Pumped

water

Spring

developme

nt

Hand

dug

well

Farm

pond

2008 1009.

1

418.1 1155.5 25.6 131 8.4

2009 2002.

2

571.01 1642.1 50 520.1 5.73 6

lxxv

3.2. Treatments, design and agronomic practices of the

experiment

There were a total of sixteen treatments made by varying the

amount of irrigation water throughout the developmental stages

(three treatments); and with possible combination of specific

developmental stages of the crop (12 treatments) (Table 3.5).

The irrigation levels were full irrigation which is 100% of Etc,

75% of Etc (25% deficit), 50% of Etc (50% deficit) and 25% of

Etc (75% deficit). The crop developmental stages were divided in

to four major periods: establishment, vegetative development,

bulbification and ripening stage. According to Allen et al. (1998)

the establishment stage runs from transplanting until

approximately 10% of ground cover (02 – 21 Feb, 2010). The

vegetative development stage run from 10% of ground cover up to

effective full cover (22 Feb - 23 Mar, 2010). The bulbification

stage runs from effective full cover to start of maturity (24

Mar - 22 Apr, 2010) and the ripening stage (23 Apr - 7 May,

2010) runs from start of maturity to harvest. Each four levels

of irrigation water were applied throughout the crop growth

stages and each the three limited irrigation amounts were

lxxvi

applied at specific growth stages of the crop. Full irrigation

was used as standard check and replicated for each treatment.

Table 3.3. Treatment combinations of the amount of irrigation

water throughout the growing season and at specific

developmental stage of onion.

Limited irrigation application at specific developmental stages

Irrigation

amount

Establishm

ent

Veg.

development

Bulbificat

ion

Ripening

75%ETc 75%0III 75%I0II 75%II0I 75%III0



75%IIII 25 % deficit throughout the crop stages



100%IIII Full irrigation (standard check)

I indicates full irrigation or the throughout deficit amount of water,0 indicates the deficit amount of water and its position indicates thestage in which the treatment applied.

The experimental plots were laid out using randomized complete

block design. Each treatment were replicated three times and

distributed randomly in each block. Each plot had an area of

lxxvii

5.4m2 with a one meter wide pathway between each plot and 2m

wide pathway between each block. Three furrows of 40cm wide each

were laid through each plot that onion seedlings were planted at

the two sides of each furrow. Each row had 30 plants and each

plot had a total of 180 plants. Totally, 60 plots, each of a

1.8m width and 3m length plots were arranged in three blocks.

The field was plowed four times (twice using tractor and twice

using oxen). It was prepared again by human labor to break the

clods, while leveling and furrow preparation was done using hand

tools. Row orientation for furrow was north to south having

three rows per plot. The commonly used onion variety in the

area, Bombey Red was nursed and seedlings were transplanted to

the main field 45 days after emergency on 2 Feb, 2010. According

to the recommended practice of Sirinka Agricultural Research

Center (SARC, 2003) seedlings were planted at the two sides of

ridges of the furrow at 10cm spacing between plants, 20cm

between rows and 40cm between furrows ridges. DAP ((NH4)2HPO4)

and Urea ((COCNH2)2) were applied at the recommended rate of

100kg/ha DAP at time of planting and 100kg Urea with split

application 50kg at time of planting and 50kg six weeks after

lxxviii

planting. All other cultural practices were followed as per the

requirement of onion crop. Prior to the application of

treatments equal amount of irrigation was applied two times for

all experimental plots to favor uniform establishment of the

seedlings.

Fig. 3.3. Experimental field with onion plants (at the end of

its establishment stage)

lxxix

3.3. Data collection and analysis

3.3.1. Analysis of soil chemical and physical

properties

The physical and chemical properties of the soil at the study

site were analyzed up to 60cm depth at the Ethiopian National

Soil Testing Center. The soil samples were collected from

different soil sampling points using an auger and combined in a

plate and mixed thoroughly to form a composite soil sample. Ten

undisturbed soil samples were taken by core sampler from

representative pits of 60cm depth, five from 0-30cm and five

from 30-60cm depths and analyzed to determine field capacity and

permanent wilting point for each horizon. Thus, the available

volumetric soil moisture (%) for each soil depth was determined

by taking the difference between soil moisture content at -

0.3bar FC and -15bar PWP suction by pressure plate apparatus

method (Table 3.7). The method of analysis of the soil chemical

and physical properties is described in table 3.4.

Table 3.4. Properties of soil analyzed and methods used

lxxx

The results of analysis of the some soil chemical and physical

properties of the experimental site are provided in tables 3.5

and 3.6, respectively.

Table 3.5. Some soil chemical properties of the experimental

site

Soil

Dept

h

pH ECe

(ds/

m)

ECw

(ds/

m)

OM

(%

)

OC

(%

)

CEC

(cmo

le

Exchangeable

Cathion

(cmole/kg)

Av.P

(ppm

)

Base

satn

(%)

Soil property Method of analysis

Electrical

conductivity

Conducto metric analysis by

conductivity meter

CEC & Exchangeable

bases

Ammonium acetate extraction method

at pH 7

Organic meter Walkely and Black method

pH H2O Potentiometric analysis by pH meter

Available Phosphorous Olsen method

Texture Bouyoucos method by hydrometer

Bulk density and

Particle density

Measurement of volume and mass by

Blake & Hartage (1986)

Total Nitrogen Kjeldahal method

Available K Morgan extraction method

FC & PWP Pressure plate apparatus by Cassel

and Nielsen (1986)

lxxxi

(cm) kg-1) K Na Ca Mg

0-30 7.

6

0.10

8

0.12

1

0.

13

1.

33

32.1

8

2.

11

0.

95

18.

6

8.

55

20.7

2

94

30-

60

7.

4

0.06

1

0.

09

0.

59

28.5

4

0.

9

0.

95

16.

06

2.

14

13.1

2

70

Table 3.6. Some soil physical properties of the experimental

site

Soil

Depth

(cm)

Particle size

(%)

Textural

class

FC

(%wt.

)

PWP

(%wt

)

Bulk

density

(g/cc)

Particle

Density

(g/cc) Sand si

lt

cl

ay

0-30 38 38 24 Loam 13.88 13.8

8

1.334 2.47

30-60 46 26 28 Sandy

clay

loam

13.19 13.1

9

1.294 2.51

Based on USDA soil texture classification the soil is found as

loam at the upper profile and sandy clay loam in the lower soil

profile with the average bulk density of 1.334 g/cc and 1.294

g/cc, respectively. The pH of the study soil is 7.5. According

to SARC (2003), the desirable soil pH for onion production

ranges from 6.5-7.5. However, onion performs well on soils with

lxxxii

pH of 7.5-7.8, provided high organic matter, nutrients of

nitrogen, phosphorus and available water (Nonnecke, 1989). In

line with this Ayas and Cigdem (2009) obtained maximum yield of

55t ha-1 with soil pH of 8.04. The electrical conductivity of the

soil extract (ECe) indicated that the soil is non-saline. There

is no soil salinity problem in the irrigable areas where the

experimental site was located as the source of irrigation water

is Jarra stream with EC value of 0.121ds/m (Flip, 2003). The

measured average available phosphorus for the experimental site

is 16.92 ppm which is responsive for onion production

(Amarasiri, 1990). The organic matter content of the area is

0.11% which is said to be low and it was supplemented with

artificial fertilizer.

3.3.2. Reference evapotranspiration, crop water

requirement and applied irrigation depth

The reference evapotranspiration (ETo) was calculated based on

the FAO Penman Monteith method (Allen et al., 1998) and estimated

using Cropwat version 8.0 software. For the computation of ETo

lxxxiii

full information of metrological data for the study area were

collected from National Metrological Agency, Kombolcha sub

branch. The climate data were temperature (minimum & maximum),

relative humidity, sunshine hours, wind speed and precipitation

from long serious of data (Appendix A). The crop water

requirement (ETc) over the growing season was estimated from ETo

and estimates of crop evaporation rates expressed as crop

coefficients (Kc) (Allen et al., 1998). It was calculated by

multiplying the reference evapotranspiration value with the

small vegetables crop coefficients given by the Cropwat software

as 0.7 for the initial stage, 0.7<Kc<1.03 for the crop

development stage, 1.03 for the mid season stage and

1.03>Kc>0.96 for the late season stage (eq.1).

The software also demands crop information on crops that is

relevant for irrigation scheduling. The average length of the

growing period of onion crop was taken as 95 days. The length of

establishment stage, vegetative development stage, bulbification

stage and ripening stage were 20, 30, 30, and 15 days (Fig 3.4).

Transplanted date was recorded and average maximum rooting depth

was taken as 45cm. The critical soil moisture level where first

lxxxiv

drought stress occurs affecting crop evapotranspiration and crop

production (critical water depletion fraction (P)) was taken

from Allen et al., (1998) (commonly known as FAO Irrigation and

Drainage paper 56) as 0.3, 0.45 and 0.5 for establishment, bulb

enlargement and ripening stages. As well, crop yield factor

(Ky), factors for the crop sensitivity to water stress was based

on information from the FAO Irrigation and Drainage paper 33 as

0.8, 0.4, 1.2 and 1 for establishment, vegetative development,

bulbification and ripening stages, respectively. Reference

evapotranspiration and crop water requirement of onion is

presented in table 3.8.

Fig. 3.4. Onion developmental stages, its duration days and the

corresponding Kc value.

lxxxv

0.7 0.7<Kc<1.03 1.03 1.03 >Kc>0.96

Allen et al., (1998) indicated the successful estimate of ETo by

observing the water loss from the pan and using empirical

coefficients to relate pan evaporation to ETo. Elliades (1988)

also reported the worldwide realization of pan evaporation based

irrigation scheduling because of its simple and easy

application. Steduto et al. (1996) cited in Maldonado et al. (2006)

explained the overestimating behavior of the Penman-Monteith

model when compared to the lysimeter data in conditions of low

evaporative demand and underestimating in conditions of high

evaporative demand. In consideration of this idea and to obtain

the evaporation rate of the area in particular, class ‘A’ pan

was taken from the Ethiopian Meteorological Agency, Kombolcha

sub branch and set near the experimental site. The evaporation

data was recorded simply by observing the daily water loss from

the pan. In the absence of rain, the amount of water evaporated

during a period (mm/day) corresponds with the decrease in water

depth in that period. When there is rain the amount of

evaporated water was calculated in consideration of the amount

of rainfall added to the pan. The pan evaporation data during

the experiment was described in appendix A, Table A.9.

lxxxvi

Table 3.7. Reference evapotranspiration and crop water

requirement (mm) of onion

Month Decad

e

Sta

ge

Kc ETo ETc ETo ETc Net Irr.

Req.

coef

f

mm/day mm/

day

mm/

dec

mm/dec mm/dec

Feb 1 Ini

t

0.7 3.79 2.65 34.14 23.9 23.9

Feb 2 Ini

t

0.7 4.06 2.84 40.57 28.4 28.4

Feb 3 Dev

e

0.74 4.15 3.07 33.11 24.5 24.5

Mar 1 Dev

e

0.84 4.24 3.56 42.38 35.6 35.6

Mar 2 Dev

e

0.95 4.33 4.11 43.26 41.1 41.1

Mar 3 Mid 1.03 4.36 4.49 47.96 49.4 49.4

Apr 1 Mid 1.03 4.40 4.53 43.98 45.3 45.3

Apr 2 Mid 1.03 4.43 4.56 44.27 45.6 45.6

Apr 3 Lat

e

1.01 4.69 4.74 46.93 47.4 47.4

May 1 Lat

e

0.96 4.95 4.75 34.69 33.3 33.3

Total 374.6 374.6

lxxxvii

For the purpose of calculation of net irrigation water amount

(ETc) obtained from the pan evaporation equation 2, whose

fundamentals are given in Allen et al. (1998) was used. By

considering the local climatic condition (wind speed and

relative humidity) the pan coefficient was taken simply as 0.75

(Allen et al., 1998).

Where: - ETc is the amount of net irrigation water (mm)

Epan is the cumulative evaporation in the

irrigation interval (mm)

Kp is the pan coefficient

Kc is the plant coefficient

The pan evaporation method indicated that ETo and ETc were 1.3%

to 8.4% under estimated by the pan evaporation method from

February to first decade of April and over estimated in the

later periods (Fig. 3.5). Thus, the calculated ETo data (Cropwat

software output) was used for the whole irrigation purposes

lxxxviii

during experimentation. Even though the software output ETc was

used for irrigating the experiment, according to the result

obtained from both methods the total evapotranspiration estimate

over the growing seasons of the crop was 376.2mm and 374.5mm

(Appendex B, Table B.1). Both methods are highly and positively

correlated (R2=0.9148). The pan evaporation method estimated the

value only 0.45% over the Penman-Monteith method which is

insignificant. Therefore, the pan evaporation method estimated

the reference evapotranspiration of the area and can be used

adequately for onion irrigation scheduling.

Figure 3.5. Correlation of reference evapotranspiration (mm/dec)

of the experimental area by using pan evaporation method and

Penman-Montheith model.

During the study period unexpected precipitation were occurred

at different stages of the crop. However, it was well recorded

lxxxix

by using standard rain gauge. Thus, each amount of rainfall was

recorded and the effective precipitation was considered in the

gross irrigation amount during each irrigation water application

(Appendix A, Table A.8). The effective rainfall was calculated

by FAO empirical formula. The total effective rainfall from

beginning to the end of the experiment was 3.6mm. This amount

can be considered as minimum compared to the total water

requirement of onion. The development of the crop can,

therefore, be considered to have depended essentially on the

application of irrigation water. The optimal or ‘no stress’

irrigation was computed by deducting the effective rainfall (if

rainfall available) from the net irrigation requirement of the

crop and then, the depth of water applied to other treatments is

taken simply as percentage of the optimal irrigation at specific

developmental stage or throughout the growing season.

The gross irrigation requirement was computed by adopting a

field application efficiency of 60%. Furrow irrigation

application efficiencies normally vary from 45-60% (Bakker et al.,

1999). Brouwer and Prins (1989) also indicated 60% as irrigation

application efficiency for furrow irrigation. In this

xc

experimental setup, water was applied with accurate measurement;

furrows were short and end-diked. As a result, there was no run-

off and the only loss would be deep percolation which is

expected to be not much in a deficit irrigation practice.

Therefore, a higher value of application efficiency (60%) was

adopted. Then, the overall discharge measurement was done at the

inlet of the supply channel always at the time of irrigation

using bucket method by using eq.3.

Where: - Q is farm channel discharge in l/s.

v is known volume of the bucket.

s is average time taken to fill the bucket.

The amount of water delivered to each treatment was estimated by

the time duration of application irrigation water (eq.4). The

duration of water application for each furrow was calculated

as:-

Where: - t is the water application time (min)

xci

Dap is gross water application depth (mm)

l is furrow length (m)

w is furrow width (m) and

Q is discharge (l/s)

Therefore, according to the required amount of water to be

applied the duration of irrigation at different treatment was

different. The result of time duration per single furrow of full

irrigation condition is indicated in appendix B, table B.2. The

depth of irrigation amounts that were applied for each treatment

per irrigation time is presented in appendix B, table B.3.

Based on the typical practice of the local farmer to irrigate

onion a fixed irrigation interval, six days was selected. Six

days irrigation interval resulted in better yield in the region

(Samson and Ketema, 2007; ARARI, 2008). For one week after

transplanting the irrigation depth of 13.1mm was applied twice

uniformly to all the treatments to favor uniform seedling

establishment. The irrigation treatment was started on 7 Feb,

2010. The total amount of water applied starting from 7 Feb,

2010 to the end of the growing period of the crop (7 May, 2010)

xcii

was 584.2mm. The lowest was applied in treatment level of

25%IIII. Table 3.8 shows the seasonal total water applied for

each treatment at each developmental stage. The table showed

that the highest amount of water was applied during mid season

stage. This is because of the highest crop water need (the

larger Kc value) and relatively longer number of days during

this growing period.

xciii

Table 3.8. Break down of total applied irrigation water (mm) to each

development stages of onion

Treatments

Establishment stage

Veg.development stage

Bulbificationstage

Ripening stage

Totalapplied Water (mm)

100%IIII 82 181 226.4 94.8 584.2

75%IIII 61.5 135.8 169.8 71.1 438.2

50%IIII 41 90.5 113.2 47.4 292.1

25%IIII 20.5 45.3 56.6 23.7 146.3

75%0III 61.5 181 226.4 94.8 563.7

50%0III 41 181 226.4 94.8 543.2

25%0III 20.5 181 226.4 94.8 522.7

75%I0II 82 135.8 226.4 94.8 538.95

50%I0II 82 90.5 226.4 94.8 493.7

25%I0II 82 45.3 226.4 94.8 448.4

75%II0I 82 181 169.8 94.8 527.6

50%II0I 82 181 113.2 94.8 471

25%II0I 82 181 56.6 94.8 414.4

75%III0 82 181 226.4 71.1 560.5

50%III0 82 181 226.4 47.4 536.8

25%IIII 82 181 226.4 23.7 513.1

I indicates full irrigation or the throughout deficit amount of water, 0 indicates the deficit amount of water, and its position indicates the stage in which the treatment applied.

3.3.3. Crop parameters

Plant height, leaf number and bolting

xciv

The height of the plant at the end of each stage was measured

from randomly selected five representative plants. The first,

the second and the third height measurement was taken at the end

of the establishment stage (21-02-2010), vegetative development

stage (23-03-2010), and bulbification stage (30-04-2010). For

all measurements representative plants from the middle ridge of

each treatment was taken. The last height measurement was taken

just before harvest and subjected to statistical analysis. The

number of leaves of representative sample plants of the onion

was counted from randomly selected five plants per plot.

Flowered onion plants in each plot were counted and percentage

of bolting was calculated as number of bolted onions per total

number of onion plants per hectare times hundred.

Fresh biomass, total bulb yield, marketable and unmarketable

bulb yields

Fresh biomass and total bulb yields per plot were measured at

harvest using sensitive balance. Unmarketable yield of onion

bulbs were selected from the total bulb and weight of both

marketable and unmarketable bulb yields were measured for each

plot. (Unmarketable yield here refers to the bulb yield with

xcv

physiological and disease problems including under sized,

splitted, and white colored.)

Average bulb weight bulb diameter and bulb size classification

Just after harvest average bulb weight and bulb diameter of five

representative bulbs were measured randomly from each plot using

sensitive balance and caliper, respectively. The local farmers

were requested for bulb size classification in to small, medium

and big classes. The size of onion bulbs in each plot were

categorized in to big, medium, and small sizes by them and their

respective weight and number of bulbs was recorded.

Harvest index and irrigation water productivity

Harvest index was calculated as the ratio of bulb yield to

biomass yield per hectare and crop water use efficiency was

calculated as the ratio of average bulb yield (Kg ha-1) to total

amount of water used (m3 ha-1).

3.3.4. Statistical analysis

xcvi

Analysis of variance (ANOVA) was made to determine crop

parameter response to irrigation using Genstat and JMP 5

statistical softwares. Means among treatments were compared

using Duncan’s multiple range test. Correlation and regression

analysis were carried out to estimate the relationship between

yield and yield components as affected by the amount of

irrigation water.

Chapter 4. Results and Discussion

4.1. Plant height

The analysis of variance indicated that application of different

irrigation water amount and its application to the different

developmental stages had very high significant (P < 0.001) effect on

plant height of onion. (The mean square table for plant height

is indicated in appendix C, table C.1). The highest mean plant

height was observed from 100%IIII (51.73cm) and the lowest mean

plant height was recorded from treatment 25%IIII (32.6cm).

Compared to 100%IIII treatment, it resulted in 36.9 % height

reduction. The result agreed with the findings of Khan et al.

xcvii

(2005) and Biswas et al. (2003) who reported higher plant height

of onion at shorter irrigation intervals. The effect of

application of deficit irrigation at the vegetative

developmental stage was higher than any other stages. Next to

treatment 25%IIII the second severe height reduction was

observed from treatment 25%I0II (35.07cm). It resulted in 32.2%

height reduction. This might be due to the effect on plant

growth which is associated with its effect on the cell division,

expansion and cell wall synthesis (Mumns, et al., 1998). As the

amount of irrigation water decreases there will be less amount

of RAW for the root and plants exert more energy to absorb

water. Hence, the division and expansion of cell will be lower

which might have resulted in shorter plant height (Mumns, et al.,

1998).

The height measurement taken at the end of developmental stages

of the crop indicated that, application of 25%, 50% and 75%

deficit irrigation at vegetative developmental stage reduce the

height increment by 14.7, 28.3 and 38.6% compared to the

100%IIII, respectively (Fig.4.1). On the other hand, application

of deficit irrigation at the crop establishment stage and

xcviii

ripening stage had little effect. Particularly, application of

deficit irrigation at the ripening stage had no effect on the

height of onion compared to other stages. Plant height was

positively and very highly significantly (P < 0.001) correlated

to fresh biomass (r=0.814) and total bulb yield (r=0.836) of

onion.

Figure 4.1. Plant height (cm) differences in treatments with

time (measurement taken at the end of each developmental stage).

4.2. Leaf number

xcix

Variation in number of leaves indicates the vigorousity of the

crop which is directly related to the potential yield of onion.

Leaf number per plant was very highly significantly (P < 0.001)

different among treatments due to application of deficit

irrigation and its application to the different developmental

stages of the crop and also significant (P < 0.05) due to its

interaction. (The mean square table for leaf number is indicated

in appendix C, table C.1). The highest mean (11.8) leaf number

per plant was obtained from treatment 100%IIII. Treatments that

were irrigated with 50% and 75% of the full irrigation at

establishment, bulbification, and ripening stages, didn’t show

significant difference in their mean leaf number. However, the

leaf numbers in treatment 50%II0I and 75%II0I were slightly

higher than treatment 50%0III and 75%0III. This might be due to

the time difference in application of treatments in which leaf

initiation might cease when bulbing starts (Sinclair, 1982).

Application of deficit irrigation at the ripening stage didn’t

affect mean number of leaves. This result agreed with Mohammed

(2004) who reported that mean leaf number per plant increased

with increasing days after transplanting reaching a maximum at

75 days after transplanting. However, water deficit at any stage

c

might have negative effect on leaf life. The slight leaf number

difference in between treatment 100%IIII and deficit water

treated treatments at the ripening stage might be due to loss of

leaves because of senescence. A decrease in root zone water

potential would result in partial or complete closure of stomata

(Allen et al, 1998; Brewster, 2008)). Continued stomatal closure

triggers photo-oxidative reactions, generating free radicals,

destabilizing membranes that become leaky, releasing cell

contents to the apoplast (Rajasekaran and Blake, 1999)

triggering a sequence of senescence reactions resulting in

desiccation. The lowest leaf number was observed from treatment

25%IIII which was 37% lower than treatment 100%IIII. The reason

for decreased number of leaves per plant with increased in water

deficit could be due to the influence of moisture on the rate of

leaf initiation and the leaf life. This result agrees with the

results of Khan et al. (2005) and Biswas et al. (2003) who reported

significant increment in leaf number per plant with decreased %

TAW depletion. The reduced number of leaves in these treatments

might be the reason for their low amount of bulb yield with high

number of small bulbs. Because, leaf number was positively and

ci

very highly significantly (P < 0.001) correlated to fresh biomass

(r=0.752) and total bulb yield (r=0.760) of onion.

4.3. Fresh biomass yield

Application of different amount of irrigation water either

throughout the developmental stages or at the specific

development stages of onion had a significant effect (P < 0.001) on

fresh biomass of onion (Appendix C, table C.2). The fresh

biomass of treatment 100%IIII was the highest (31.5t ha-1) (Table

4.1). However, it was not statistically different from treatment

of 75%0III (28.9t ha-1), 75%III0 (28.1t ha-1), 75%I0II (25.1t ha-

1) and 50%III0 (24.4t ha-1). Next to these treatments, the fresh

biomass obtained from treatment 75%IIII (24.0t ha-1) was higher

than the rest irrigation treatments. The lowest fresh biomass

was obtained from treatment 25%IIII (7.2t ha-1) followed by

treatment 25%II0I (9.6t ha-1). The result indicated that as the

amount of irrigation water increased from 75% deficit to full

irrigation, the fresh biomass yield also increased linearly

(Fig.4.2). The result is in line with Ayas and Cigdem (2009) and

Pandy et al. (2001) who reported the linear relationship between

cii

amount of irrigation water and biomass production. Even if the

linear relationship was true the additional fresh biomass due to

the additional water used in fully irrigated treatment was

insignificant compared to the amount of water saved by

treatments 75%0III, 75%III0, 75%I0II and 50%III0.

EMBED Excel.Sheet.8

y = 0.233x -104.0R² = 0.973

0

5

10

15

20

25

30

35

510 520 530 540 550 560 570 580 590

ciii

Fres

h bi

omas

s yi

eld

(t/h

a)

Fres

h bi

omas

s yi

eld

(t/h

a)

Fres

h bi

omas

s yi

eld

(t/h

a)

Fres

h bi

omas

s yi

eld

(t/h

a)

applied irrigation depth (mm) throughout the crop stages

EMBED Excel.Sheet.8

y = 0.116x -36.93R² = 0.973

0

5

10

15

20

25

30

35

400 450 500 550 600

Water deficit during establishment and ripening stages had

insignificant effect on the fresh biomass of the crop. It

resulted in a yield reduction of 8.2% and 10.8% in treatment

civ

applied irrigation depth (mm) at ripeningstage

applied irrigation depth (mm) at veg. development stage applied irrigation depth (mm) at bulbification stage

Fres

h bi

omas

s yi

eld

(t/h

a)

Fig. 4.2. Relation between fresh biomass (t ha-1) yield and thecorresponding applied irrigation depth (mm) throughout and at

75%0III and 75%III0, respectively. The lower the yield reduction

at establishment stage might be attributing to its ability to

partially recover from the effect of early water stress. Pandy et

al. (2001) obtained sufficient above ground biomass in wheat when

it was imposed for water deficit at the earlier growth stage.

The lower the yield reduction at the ripening stages might be

attributed to low water requirement of the crop late in the

ripening stage.

The result revealed that vegetative developmental and bulb

enlargement stage is the most susceptible stages for moisture

stress that water deficit at these stages significantly reduce

fresh biomass of onion. As compared to 100%IIII, treatment

25%I0II and 25%II0I encountered 69.5% and 53.01% fresh biomass

reduction, respectively. Even, treatment 75%II0I and 75%I0II

encountered yield reduction of 31.4% and 20.3%, respectively

which is by far higher than the yield reduction caused by the

water deficit at establishment and ripening stages of onion.

This is similar to Bazza and Tayya (1999) who reported stressing

the crop during bulbification stage reduces the yield

significantly than stressing the crop during establishment and

cv

ripening stages. Fresh biomass weight was positively and very

highly significantly (P < 0.001) correlated to total bulb yield

(r=0.970) of onion.

4.4. Total bulb yield

Total bulb yields were very highly significantly affected by

deficit irrigation water applications (P < 0.001) either

throughout the crop development stages or application at the

specific development stage of onion. Interaction effect of water

deficit and crop developmental stages was also very highly

significant (P < 0.001) for the reduction of total onion bulb

yield (Table 4.1). The mean square value for total bulb yield is

presented in appendix C, table C.2. Application of full

irrigation increased total bulb yield to 26.2t ha-1. However, it

was statistically the same with treatment 75%0III, 75%III0 and

treatment 50%III0 with a total bulb yield of 25.8, 26 and 23.9t

ha-1, respectively. This means, the additional irrigation water

(205, 237, 474m3 ha-1, respectively) consumed by this treatment

didn’t bring significant additional bulb yield. Treatment

75%IIII resulted in 20.09% bulb yield reduction. However, it had

cvi

9.4%, 17.4%, and 53.68% bulb yield increment over treatment

50%0III, 75%II0I and 50%IIII, respectively. In terms of water

productivity 20.09% yield reduction was insignificant that the

saved water from this treatment can produce 7.97% bulb yield

over treatment 100IIII. Even though, the water saved in

treatment 25%IIII was the highest, its impact on yield was more

severe. The yield loss in this treatment was 85.44% which was

hard to compensate with the saved water.

The finding revealed that the total bulb yield loss due to

moisture stress was linear. Similarly, linear relationship was

observed between irrigation water with yield (R2=0.97) in green

house experiment (Ayas and Sigdem, 2009). Lemma and Shimelis

(2003) also observed yield increment from 12.9 to 17t ha-1 as the

amount of water applied increased from 3 to 7cm depth. The

significant effect of irrigation water application was reported

by many researchers (Biswas et al., 2010; Faten et al., 2010; Orta

and Ener, 2001; Kumar, et al., 2007; Ayas and Sigdem, 2009; Lemma

and Shimelis, 2003). The improvement of total yield response to

high amount of total water application could be attributed to

the enhancing effects of water to crops biological functions and

cvii

growth in addition to the improving effects of water on nutrient

availability.

The results of analysis of variance for total bulb yield also

showed that there was highly significant (P < 0.001) difference

among the sensitivity of crop developmental stages to moisture

stress. In contrast to Urrea et al. (2003), in which the highest

garlic bulb yield was obtained from no water restriction during

the ripening period, water deficit at the establishment and

ripening stages of onion brought the highest bulb yield than the

other crop stages. Water deficit imposed during bulbification

stage and vegetative development stage resulted in highly

significant yield reduction. A yield reduction of 37.8% and

32.5% were recorded for these stages, respectively. While 17.1%

and 12.8% yield reduction were associated with water deficit

applied during the establishment and ripening stages of onion,

respectively. The result is in agreement with Van Eeden and

Mybungh (1971) which showed that water stress imposed late in

the season reduced onion total bulb yield by 15%. From deficit

irrigation experiments on vegetables and cereals, it was found

that lowest yield is obtained during 75% deficit throughout the

cviii

growing season; however, stressing the crops during

establishment and ripening stage of the growing season does not

affect the crop yield significantly (Bazza and Tayaa, 1999).

Irrigation water deficit applied at different developmental

stages had different effect on bulb yield of onion (Table 4.1).

Severe yield reduction was brought by treatment 25%II0I (6.9t

ha-1). It caused about 73.5% yield reduction compared to

100%IIII. This indicates that bulbification stage is the most

sensitive stage for moisture deficit. The highest the yield

reduction at this stage is in agreement with many authors

(Samson and Ketema, 2007; Yenesew and Tilahun, 2009; Singh and

Aldefer, 1996). This period coincides with the highest water

requirement and the crop cannot withstand water deficit without

substantial reduction on yield. Dragland (1974) also reported

that three weeks long water stressed onion in early

developmental stage reduced onion yield more than when imposed

near the end of the growing season. The higher the total bulb

yield reduction at vegetative developmental stage might be

associated with reduction of leaf expansion which can result in

poor net photosynthetic capacity of plants. On the other hand,

cix

water deficit during establishment and ripening stage had a

limited effect on yield. The less sensitivity of onion at the

initial stage might be attributed to its fast compensation

capability for the early water stress. Asseng et al. (1998)

indicated that water uptake rate increased quickly after

rewetting and exceeded the uptake rate of the non stressed

treatment at about 2-3 weeks after the deficit is released.

The yield reduction from treatment 75%0III and 75%III0 was

insignificant compared to the yield obtained from 100%IIII. The

yield reduction caused by treatment 75%III0 was almost nil,

which is only about 0.8% reduction. But the amount of irrigation

water consumed by this treatment is 4% less than the water

consumed by 100%IIII. While greater than 25% deficit irrigation

at the mid and vegetative developmental stages caused a yield

reduction that was equivalent with 50% and less irrigation water

application throughout the crop growth stages.

cx

4.5. Marketable and unmarketable bulb Yields

The ANOVA on marketable yield of the treatments indicated the

very high significant effect (P<0.001) of variation in irrigation

water amount either throughout the whole growing season or at

specific phenological stage of the crop (Appendix C, Table C.2).

Unlike the yield components, the increase in irrigation water

amount didn’t increase marketable yield of onion proportionally

(Table 4.1). Even though, the highest (21.5t ha-1) marketable

bulb yield was obtained from treatment 100%IIII, it accounted

marketable bulb yield loss of 17.9%. This value was greater

compared to 9.6%, and 12.9% yield loss of treatment 75%III0 and

treatment 50%III0, respectively. Compared to its total bulb

yield the highest marketable yield loss was occurred from

treatment 25%II0I (59.9%) and 25%IIII (47.3%). Even though, the

water saved in these treatments was the highest, its impact on

marketable bulb yield was more severe. Compared to 100%IIII, the

loss recorded in these treatments was 66.5% and 62.9%,

respectively. This might be due to the large number of small and

immature bulbs introduced due to the water stress.

cxi

Interaction effect of water deficit and crop development stages

was also very highly significant (P < 0.001) for the variation of

marketable yield. Application of 25% deficit irrigation at the

ripening stage of the crop increased marketable bulb yield of

onion by 9.3% over the control. The marketable bulb yield

obtained from 100%IIII was not statistically significantly

different from treatment 75%0III (20.6t ha-1), 75%III0 (23.5t ha-

1), and 50%III0 (20.8t ha-1). This result disagreed with the work

of Singh and Aldefer (1996) that soil water stress at any

developmental stages leads to reduction of marketable yield. But

it is in line with ARARI (2008) that as the amount of applied

irrigation water increases, the amount of marketable yield will

decrease due to the increase in unmarketable yield components

like split, decay and bolt. Therefore, application of full

irrigation water at the ripening stage of onion doesn’t

necessarily increase marketable bulb yield.

cxii

Table 4.1. Amount of water, developmental stages and their

interaction effects on fresh biomass, total bulb yield,

marketable and unmarketable bulb yield of onion.

Treatments

Fresh

biomass

Total bulb

Yld Mrk Yld Unmrk Yld

100%Irr 31.5a 26.17a 21.52a 4.78b

75%Irr 24.89b 21.6b 18.45b 3.65ab

50%Irr 20.35c 17.28c 13.99c 3.55a

25%Irr 12.75d 10.21d 7.77d 3.15a

LSD0.05 11.897 1.319 1.376 0.853Throught 20.07b 16.13b 12.77a 3.37

Establish 25.48a 21.57a 17.11b 4.23

Veg.dev. 21.72b 17.54b 15.23b 3.88

Bulbifn 20.17b 16.17b 12.12a 3.8

Ripening 25.03a 22.67a 19.93c 3.64

LSD0.05 2.121 1.474 1.538 NSInteraction effect of irrigation amount and

growth stage of the crop

100%IIII 31.5a 26.2a 21.5ab 4.8a

75%0III 28.9ab 25.8a 20.6abc 5.2a

75%III0 28.1ab 26a 23.5a 2.5ef

75%I0II 25.1abc 20.2cd 17.5bcd 2.8cdef

50%III0 24.4abcd 23.9ab 20.8abc 3.1bcde

75%IIII 24.0bcd 20.9bc 16.7cde 4.2abcd

50%0III 23.3cd 19.1cde 15.1def 3.7abcd

50%I0II 22.3cd 17.7def 12.8efg 4.7a

75%II0I 21.6cde 17.8def 13.9ef 3.8abcd

cxiii

25%III0 19.4de 18.6cdef 14.2ef 4.4abc

50%II0I 17.9de 13.9fg 10.4gh 3.6abcde

25%0III 17.4def 15.2efg 11.8efg 3.17abcde

50%IIII 16.8ef 13.6fgh 10.9fgh 2.7def

25%I0II 14.8fg 11.1hi 7.9hi 3.2abcde

25%II0I 9.6gh 6.9ij 2.9ij 4.0abcde

25%IIII 7.2h 3.8j 2j 1.8f

LSD0.05 4.243 2.948 3.077 1.05CV (%) 11.1 9.2 12.1 30.4

Mrk = Marketable, Unmrk = Unmarketable, Yld = Yield, NS = Non significant, Means in the same column followed by the same letter are not significantly different at P < 0.05, I indicates full irrigation or the throughout deficit amount of water, 0 indicates the deficit amountof water, and its position indicates the stage in which the treatment applied.

The effect of the amount of irrigation water applied was highly

significant (P < 0.01) for unmarketable yield. But, there was no

statistically significant effect among its application to the

specific developmental stages of the crop and its interaction.

However, there was slight difference among them. Deficit

irrigation water application at the initial stage recorded the

highest unmarketable bulb yield than the other crop stages. In

contrast, application of deficit irrigation at the ripening

stage reduce unmarketable bulb yield.

Application of full irrigation at the ripening stages resulted

in the highest unmarketable bulb yield than the rest irrigation

cxiv

amounts (100%IIII (18.3%) and 75%0III (19.3%)). Similarly,

ARARI (2008) found that irrigating 30mm per four and seven days

irrigation interval gave high unmarketable bulb yield than ten

and thirteen days irrigation interval. This is because as the

amount of applied irrigation water increases the amount of

unmarketable yield components, like split, decay and bolt

increases.

4.6. Average bulb weight

The results of analysis of variance showed that there was very

highly significant (P < 0.001) different effect among the

different irrigation water applications, its application to

specific developmental stages and their interaction (P < 0.01) on

average bulb weight per plant (Appendix C, table C.3 and table

4.2). The average bulb weight of onion increased from 51.3%

(treatment 25%IIII) to 84.2% (treatment 75%IIII) as the amount

of water used by the plant increased from 25% to 75% of the full

irrigation. In between these, 35% of bulb weight reduction

occurred due to half of the full irrigation water application

(treatment 50%IIII). Unit bulb weight increased linearly with

cxv

increasing applied water (Hanson et al., 2003). In line with this

Al-Harbi (2002) also indicated the increase in average bulb

weight at higher level of irrigation water. Application of 25%

deficit irrigation throughout the plant growth stages (treatment

75%IIII) resulted in 15.8% bulb weight reduction compared to the

control which was better than 75% water deficit at any stage as

well as 50% and 75% water deficit throughout the crop

phenological stages. Water deficit at the bulbification stage of

the crop resulted in less average bulb weight than the other

stages (51.05g in treatment 25%II0I, 62.07g in treatment

50%II0I, and 69.8g in treatment II0I). The highest average bulb

weight was obtained from treatment 100%IIII. However, it was

statistically the same with treatment 75%I0II (94.3g), 75%III0

(89.6g), 75%0III (96.9g) and 50%0III (91g). This result

disagreed with the finding of Urrea et al. (2003). The authors

found a significant effect on bulb size of garlic when the

amount of water varied at the ripening stage. Application of 25%

deficit irrigation at the initial stage of onion had only 3.7%

bulb weight reduction, while 49% bulb weight reduction was

observed in application of 75% deficit at the bulbification

stage (treatment 25%II0I). The finding indicated that

cxvi

application of deficit irrigation at the initial stage has less

effect on bulb weight of onion than other stages. Average bulb

weight was very highly significantly (p < 0.001) and positively

correlated with leaf number(r=0.692) and plant height (r=0.750).

Table 4.2. Amount of water, developmental stages and their interaction effects on mean bulb weight of onion

Irrigatio

ns

Av.bulb wt.

(gm) Plant sages

Av.bulb wt.

(gm)

25% irr 58.28d Establishment 87.38b

50%irr 75.51c Veg. develop 83.66b

75% irr 86.86b Bulbification 70.73a

100% irr 101.2a Ripening 85.82b

Throughout 74.75a

LSD0.05 4.46 LSD0.05 4.99

Interaction effect of plant stage

and water amount

Plant stages

Veg.dev

t Estabt Ripen Bulbfn Throughout

25%irr 57.9fg 62.3efg

69.1def

g 51.0g 51g

50%irr 80.3cde 91abc 79.3cde 62.1efg 64.8efg

75%irr 94.3abc 96.93abc 89.6abc 69.8def 83.7bcd

Full irr 102.07a 99.27a 101.2a 100a 99.5a

LSD0.05 9.98

CV(%) 7.5

cxvii

Means in the same column followed by the same letter are notsignificantly different at p < 0.05, LSD = Least significant difference, CV = coefficient of variation

4.7. Bulb diameter

Differences in mean bulb diameter per plant due to differences

in amount of irrigation water application were very highly

significant (P < 0.001) (Appendix C, Table C.3). It resulted in

maximum and minimum bulb diameter of 6.6cm in treatment 100%IIII

and 3.5cm in treatment 25%IIII, respectively (Table 4.3). A

significant bulb diameter increment with increasing of

irrigation water also mentioned in Al-Harbi (2002), Orta and

Sener (2001) and Kumar et al. (2007). The best yields were

recorded from the highest irrigation amount associated with the

higher percentage of bulbs having diameter greater than 45 mm

(Kumar et al., 2007). Application of 25% deficit irrigation

throughout the crop stages resulted in only 8.1% bulb diameter

reduction compared to the other amounts. Severe reduction (47%

bulb diameter reduction) was occurred in treatment 25%IIII.

Bulbing involves the swelling of leaf sheaths and thickening of

cxviii

leaf sheaths occurs as a result of lateral expansion of cells.

High water deficit might have decreased the expansion of leaf

sheath cells. Average bulb diameter was very highly

significantly (P < 0.001) and positively correlated with leaf

number (r=0.678). Thus, the larger bulb diameter with increased

irrigation amount could also be attributed to the higher amount

of light intercepted by leaves which result in higher assimilate

production as the result of high number of leaves and the

partitioning of this assimilate to bulb.

There was also high significant difference (P < 0.01) in average

bulb diameter with plant growth stages in response to the amount

of irrigation water. Water stress created at bulbification stage

caused the highest bulb diameter reduction compared to other

crop stages. Particularly, 50% and less amount of irrigation

water application at the bulbification stage strongly affect

bulb diameter of onion (24.5%) compared to 14.4%, 17.6% and

16.8% bulb diameter reduction by the same amount of irrigation

at establishment, ripening and vegetative developmental stages,

respectively.

cxix

Table 4.3. Amount of water, developmental stages and their

interaction effects on mean bulb diameter of onion bulbs

Irrigatio

ns

Av. bulb

diameter (cm) Plant sages

Av. bulb

diameter (cm)

25% irr 6.56a Establishment 5.9b

50%irr 5.87b Veg. develop 5.62ab

75% irr 5.34c Bulbification 5.31a

100% irr 4.6d Ripening 5.74ab

Throughout 5.37a

LSD0.05 0.301 LSD0.05 0.337

Interaction effect of plant stages and

irrigation amount

Plant stages

Veg.devt Estabt Ripen Bulbfn Throughout

25%irr 4.6def 5.6abcd 5.1cde 4.2ef 3.5f

50%irr 5.4abcd 5.6abcd 5.5abcd 4.9cde 5.3bcde

75%irr 5.8abcd 5.9abc 5.8abcd 5.6abcd 6.1abc

Full irr 6.4a 6.5a 6.4a 6.6a 6.5a

LSD0.050.674

CV (%) 7.3

Means in the same column followed by the same letter are notsignificantly different at p < 0.05, LSD = Least significantdifference, CV = coefficient of variation

cxx

4.8. Weight and Number of Bulbs for Bulb Size Classes

The ANOVA on weight of different bulb size classes indicated

that there was very highly significant difference (P < 0.001) for

bigger and medium size bulbs among treatments (Appendix C, Table

C.4). Figure 4.4 shows the picture for each graded bulb size

classes. The analysis of variance indicated that as the amount

of irrigation water increased the weight of bigger bulb class

also increased (Table 4.4). The highest bigger bulb yield was

obtained from treatment 100%IIII and the least was from

treatment 25%IIII. The bulb yield of bigger class obtained from

treatment 75%IIII was 7.07t ha-1. Its rank was best next to

treatment 75%0III (11.2t ha-1), 75%III0 (12.6t ha-1), 50%III0

(9.2t ha-1) and 100%IIII (12.4t ha-1). Treatment 100%IIII and

75%III0 were significantly higher than any other treatments. The

lowest bigger bulb size in terms of weight and number was found

from treatment 25%IIII (0.6t ha-1). Compared to the check

(100%IIII), the reduction for this bulb class in this treatment

was almost 95% followed by 86.3% big size bulb yield reduction

from treatment 25%II0I. Since bulb size classification was done

by the local farmers, the number of bigger class onion bulbs per

cxxi

unit weight was not significantly different for all treatments.

Therefore, weight of the bulb yield obtained from each treatment

was proportional to its number.

The weight of medium bulb size obtained from the experiment

followed the same trend as the weight of the big size class. The

highest medium size bulb yield weight was obtained from 100%IIII

(10.63t ha-1) and the least was from treatment 25%IIII (1.97t ha-

1). Big and medium size bulb yields were also significantly high

as the control in treatments 75%IIII (7.9t ha-1), 75%0III (8.4t

ha-1), 50%0III (7t ha-1), 75%III0 (9.7t ha-1), 50%III0 (8.2t ha-1),

and 25%III0 (7.1t ha-1). From these treatments, treatment

75%IIII consumed 25% less water than treatment 100%IIII and gave

reasonable amount of big and medium size bulbs. The amount of

saved water as well as the reasonable amount of bigger and

medium bulbs of this treatment made it one of the best

alternatives. Most of the treatments that were subjected for 50%

and 25% water deficit either at the establishment stage or at

the ripening stage respond well for medium size bulb. Mart´ın

de Santa Olalla et al. (2004) indicated the significant weight

percentage increment of 75 to 90 mm sizes as the water dose

cxxii

increases at ripening stages. In contrast, this finding

indicated water deficit at the establishment and ripening stage

of the crop had less effect on bulb sizes relative to the effect

of water deficit created on the other two stages. The evidence

from the experiment is that 25% deficit irrigation water

application throughout the whole growing season, 50% and 25%

deficit water application either at the establishment period or

at the time of ripening of onion gave reasonable amount of

desirable bulb sizes.

The ANOVA result on small size bulbs indicated that there was

very highly significant difference (P < 0.001) between small size

bulbs among treatments (Appendix C, table C.4 and table 4.9).

Figure 4.3 indicates the weight of bigger and small size bulb

classes for each treatment. The effect of the treatment on mean

bulb weight of onion was statistically not different. However,

the corresponding numbers of small bulbs obtained in 25%IIII and

25%II0I treatment were 214.9% and 213.2% greater than small

bulbs obtained in full irrigation application, respectively. The

number of small bulbs obtained from the throughout water deficit

was significantly higher than the full irrigation. This means

cxxiii

that full stress throughout the crop phenological stages can

increase the number of small bulbs at the expense of big and

medium size bulbs. The deficit irrigation water application at

vegetative development and bulbification stages also highly

increase the number of small bulbs than the other two stages.

Figure 4.3. Weight of bigger and small size bulb classes per

treatment

cxxiv

Small size bulb Medium size

bulb Bigger size bulb

Figure 4.4. Bulb sizes classified as small, medium, and bigger

size.

Table 4.4. Weight of each bulb size classes and their

corresponding numbers as affected by irrigation amount,

developmental stage of the crop and their interaction.

Treatments Big size bulbs Med. size bulbs

Small size

bulbs

Irrigation

s

Weight

(t ha-

1) No*1000

Weight

(t ha-

1) No*1000

Weigh

t (t

ha-1)

No*100

0

100% 12.47a 114.6d 10.63d 138.3c 3.29a 73.7a

75% 9.05b 72.84c 7.95c 115.9b 5.34ab 139.4b

50% 6.11c 72.84b 6.09b 99.6b 5.61c 171.6c

25% 3.5d 72.84a 3.97a 69.3a 4.09ab 216.4d

cxxv

LSD0.05 1.096 10.39 0.92 12.51 0.937 14.21

Plant

stages

Establishm

t 9.04bc 75.77bc 7.68bc 113.4ab 4.93a 133.2a

Veg.

develpt 7.35ab 66.38ab 6.45ab 100.2ab 4.38a 158.5b

Bulbificat

ion 6.32a 60.03ab 6.53ab 94.3a 4.53a 173.6b

Ripening 10.27c 87.96c 8.9c 119.6b 4.59a 118.7a

Throughout 5.93a 57.1a 6.23a 101.4ab 4.48a 167.4a

LSD0.05 1.226 11.62 1.009 13.98 1.048 15.89

Interaction effect of amount of irrigation water and plant

stages

100%IIII 12.37a 106.1a 10.63a 140.1a 3.33a 81.6e

75%IIII 7.07bcd 62.3bcd 7.9abcd 122.2ab 5.9a 142.6d

50%IIII 3.7def 41.4cde 4.43defg 82.7bcd 5.4a 201.2abc

25%IIII 0.6f 3.09f 1.97g 60.5cd 3.2a 257.3a

75%0III 11.2ab 74.1abc 8.4abc 125.9ab 6.2a 129.1d

50%0III 6.97bcd 61.7bcd 7abcd 110.6abc 5.2a 153.1cd

25%0III 5.43cde 53.1cde

4.77cdef

g 79.0bcd 5.03a 175.9bcd

75%I0II 7.4bcd 63.0bcd 6.1bcdef 98.1abc 5.17a 166.7bcd

50%I0II 6.5cd 54.9cd

5.73cdef

g 103.7abc 5.0a 167.9bcd

25%I0II 3.1def 34.6cde 3.33efg 60.6cd 4.07a 224.6ab

75%II0I 6.9bcd 61.7bcd 7.6abcd 112.4abc 5.7a 156.8cd

50%II0I 4.2def 40.7cde

5.07cdef

g 80.2bcd 5.9a 207.4abc

25%II0I 1.7ef 22.8de 2.73fg 48.1d 3.23a 255.6a

75%III0 12.6a 103.1ab 9.7ab 120.9ab 3.6a 103.0e

cxxvi

50%III0 9.2abc 77.2abc 8.2abcd 120.9ab 6.5a 128.4de

25%III0 6.7bcd 55.6cd 7.1abcde 98.1abcd 4.93a 171.6bcd

LSD0.05

2.451 23.24 2.018 27.97 2.096 31.78

CV (%) 19.1 20.2 17 16 27.7 12.8

Means in the same column followed by the same letter are notsignificantly different at p < 0.05 I indicates full irrigation or thethroughout deficit amount of water, 0 indicates the deficit amount ofwater, and its position indicates the stage in which the treatmentapplied.

The number of small bulbs in treatment 75%IIII were reduced by

44.5% and 29.1% compared to the 75% and 50% deficit water

application, respectively. Particularly, treatment 25%II0I

resulted in 213%, 79.2%, 95.3% and 142% increment in number of

small bulbs over treatments 100%IIII, 75%IIII, 75%0III and

75%III0, respectively. While treatment 25%I0II resulted in

192.4%, 57.1%, 71.1%, and 112.1% increase in number of small

bulbs over treatments 100%IIII, 75%IIII, 75%0III and 75III0,

respectively. This indicates water stress applied at

bulbification stage of the crop could increases number of small

bulbs than any other stages of the crop followed by stress at

vegetative stages. In line with this Mart´ın de Santa Olalla et

al. (2004) found that water restrictions at the development and

bulbification stages increase the weight percentage of small

bulbs (< 60mm sizes).

cxxvii

4.9.Bolting

Bolt development in onion needs low temperature (9-17oC) with an

adequate moisture supply. In Upper Awash region of Ethiopia,

September to February supplemented with low humidity is good

condition for flower stalk emergency (Lemma and Herath, 1994).

The experimental period might be the reason that the number of

bolted onion in the experiment was low in general. However, the

maximum number of bolted onion was obtained from treatment

100%IIII (6132 bolts ha-1) and the lowest was from treatment

25%IIII (647 bolts ha-1). In the order of percentage of bolting

1.8%, 0.75%, 0.38% and 0.2% of the onion plants got bolting in

treatment 100%IIII, 75%IIII, 50%IIII, and 25%IIII. Treatment

25%IIII reduced bolting problem 80% over treatment 100%IIII.

Application of deficit irrigation late in the season also

significantly reduce bolting problem. Almost for all the

treatments the trend of bolting was linear with the amount of

irrigation water (Fig.4.5). As the amount of irrigation water

increased bolting was also increased. This finding is in

agreement with ARARI (2008) that as the irrigation frequency

increased bolting also increased. This indicates that by

cxxviii

applying deficit irrigation it is possible to control bolting

problem. On the other hand, for the purpose of seed production

full irrigation at ripening stage of the crop might increase

flowering of onion that deficit irrigation late in the ripening

stage decrease percentage of bolting.

Figure 4.5. Percentage of bolted onion plants per treatment

4.10. Harvest Index

As harvest index is the ratio of bulb yield to biomass yield, it

signify physiological ability of a crop to convert proportion of

cxxix

dry mater into economic yield, thus the higher the harvest index

the more productive efficiency of a crop (Evans, 1993). The

results of analysis of variance showed that there was very

highly significant (P < 0.001) difference among the different

irrigation water applications, its application to each

developmental stages and their interaction (P < 0.01) on the

harvest index of the crop. The highest harvest index was

obtained from treatment 50%III0 (97.7%). This value is much

higher than the average harvest index of onion which is 70-80%

(Brewster, 2008). This might be due to the senescence of plant

parts other than the bulb. Brewster (2008) indicated that the

percentage of total weight in the bulb continue to increase

after the optimum time for harvest (80% of plants have soft neck

and 80% of the shoot weight is in the bulb). The finding

indicated that application of 25% deficit irrigation throughout

the crop phonological stages increase the harvest index of onion

by 7.07% over the throughout full irrigation. The minimum

harvest index (52%) was obtained from the treatment 25%IIII. The

water stress in this treatment reduced the harvest index by

36.5%. Application of deficit irrigation at the ripening stage

of the crop increased the harvest index of onion from 12.8 %

cxxx

(treatment 75%III0) to 19.4% (treatment 50%III0) over 100%IIII.

On the other hand water deficit greater than 25% of the full

irrigation at bulbification stage of onion significantly reduces

its harvest index.

4.11. Crop water productivity

Crop water productivity (CWP) in terms of total fresh bulb yield

and marketable yield was estimated by dividing total fresh tuber

yield to the total irrigation water applied, and marketable

yield to the total irrigation water applied, respectively. The

highest CWP in terms of total bulb yield was obtained from

treatment 75%IIII (4.77 kg/m3) followed by treatment 50%IIII

(4.66kg/m3), 75%III0 (4.64kg/m3) and 75%0III (4.58kg/m3) (Table

4.6). Deficit irrigation water applications increased the CWP of

onion by 6.47% in treatment 75%IIII, 3.92% in treatment 50%IIII,

2.16% in treatment 75%0III and 3.54% in treatment 75%III0. This

indicates that more water was saved by producing more bulb yield

per m3 of applied water in relative to the 100%IIII irrigation

water application. This finding agreed with Samson and Ketema

cxxxi

(2007), Heping (2003), Salkini and Oweis (1993), Ouda et al.

(2010), Yenesew and Tilahun (2009).

Treatment 75%IIII consumed 25% less water as compared to

100%IIII, though; yield was reduced by 20.5% (5.3t ha-1). If the

saved water is used to produce onion at the same irrigation

scheduling, it will produce bulb yield of 6.97t ha-1. And this

exceeds the loss of onion bulbs occurred due to deficit

irrigation by 1.67t ha-1. This implies that it can bring 7.97%

area of land in to production and increasing the irrigated area

with the saved water would compensate for any yield loss.

Table 4.5. Actual yield loss, saved water and net yield

gain/loss as compared to the calculated yield.

Totalbulbyield

Yieldloss

Waterused

Savedwater

Calculatedyieldfromthesavedwater

Netyieldgain/loss

Extralandthatcan beirrigated fromthe

cxxxii

savedwater

Treatment

s t ha-1

t ha-

1 m3/ha m3/ha t ha-1 t ha-1 %

100%IIII 26.2 5842 0

75%IIII 20.9 5.3 4381.5 1460.5 6.97 1.67 7.97

50%IIII 13.6 12.6 2921 2921 13.60 1.00 7.35

25%IIII 3.8 22.4 1463 4379 11.37 -11.03

75%0III 25.8 0.4 5637 205 0.94 0.54 2.09

50%0III 19.1 7.1 5432 410 1.44 -5.66

25%0III 15.2 11 5227 615 1.79 -9.21

75%I0II 20.2 6 5389.5 452.5 1.70 -4.30

50%I0II 17.7 8.5 4937 905 3.24 -5.26

25%I0II 11.1 15.1 4484.5 1357.5 3.36 -11.74

75%II0I 17.8 8.4 5276 566 1.91 -6.49

50%II0I 13.9 12.3 4710 1132 3.34 -8.96

25%II0I 6.9 19.3 4144 1698 2.83 -16.47

75%III0 26 0.2 5605 237 1.10 0.90 3.46

50%III0 23.9 2.3 5368 474 2.11 -0.19

25%III0 18.6 7.6 5131 711 2.58 -5.02

I indicates full irrigation or the throughout deficit amount of water,0 indicates the deficit amount of water, and its position indicates the stage in which the treatment applied

Salkini and Oweis (1993) found that supplementing only 50% of

the rain fed crop irrigation requirement reduce crop yield only

by 10-20% relative to full irrigation. Using the saved 50% to

irrigate an equal area gives a much greater return in the total

production. Treatment 50%IIII, 75%0III, and 75%III0 consumed

50%, 3.5% and 4.1% less water as compared to the check. Though

cxxxiii

yield was reduced by 47.9 % (12.6t ha-1), 1.8% (0.4t ha-1), and

1.1% (0.2t ha-1), respectively (Table 4.5). If the saved water

from these treatments is used to produce onion, it will produce

13.6, 0.94, and 1.1t ha-1 of bulbs and would have brought a net

yield of 1.0, 0.54 and 0.9 t ha-1, respectively. This suggests

that increasing the irrigated area with the saved water would

have brought 7.35, 2.09 and 3.46% area of irrigated land. These

verify that following such deficit irrigation scheduling under

limited water supply will have a paramount importance in

bringing more land under cultivation and so more beneficiaries.

cxxxiv

Figure 4.6. Yield loss due to water deficit and yield gain from

the saved water

The least CWP was recorded from treatment 25%II0I (1.67kg/m3)

followed by treatment 25%I0II (2.3kg/m3). This can be attributed

to the higher water demand at these onion stages for bulb

formation and vegetative development. Mondal et al. (1986)

reported that once bulbing starts the onion plant will cease to

produce new leaves. Therefore, every agronomic operation can

influence bulbing rate via its effect on foliage growth and leaf

area index prior to bulbing.

Crop water productivity obtained in terms of marketable bulb

yield (CWPm), excluding the unmarketable one, was lower than the

CWP of the total bulb yield (CWPt). The highest value is

obtained from treatment 75%III0 (4.19kg/m3) followed by 50%III0

(3.87kg/m3) and 75%IIII (3.81kg/m3) (Table 4.6). This result is

different from the result obtained for CWP in terms of total

bulb yield. The finding revealed that reducing the amount of

irrigation water late in the ripening stage improves the water

productivity for marketable bulb yield from 5.2% to 13.1%. This

cxxxv

can be due to the contribution of moisture deficit for the crop

quality character like color, firmness and texture. ARARI (2008)

indicated that as the amount of applied irrigation water

increases the amount of unmarketable yield components, split,

decay and bolt increases. Therefore, application of full

irrigation water at the ripening stage of onion will reduce the

productivity of water for marketable yield.

Table 4.6. Crop water productivity (kg m-3) of onion in terms of

total bulb yield (CWPt) and marketable bulb yield (CWPm).

Total

bulb

yield

Marketa

ble

yield

Appli

ed

water CWPt Rank CWPm Rank

Treatmen

ts

t ha-

1 t ha-1 m3 ha-1 Kg m-3 Kg m-3

100%IIII 26.2 21.5 5842 4.48 5 3.68 5

75%IIII 20.9 16.7

4381.

5 4.77 1 3.81 3

50%IIII 13.6 10.9 2921 4.66 2 3.73 4

25%IIII 3.8 2 1463 2.60 14 1.37 15

75%0III 25.8 20.6 5637 4.58 4 3.65 6

50%0III 19.1 15.1 5432 3.52 10 2.78 8

25%0III 15.2 11.8 5227 2.91 13 2.26 12

75%I0II 20.2 17.55389.

5 3.75 7 3.25 7

cxxxvi

50%I0II 17.7 12.8 4937 3.59 9 2.59 11

25%I0II 11.1 7.9

4484.

5 2.48 15 1.76 14

75%II0I 17.8 13.9 5276 3.37 11 2.63 10

50%II0I 13.9 10.4 4710 2.95 12 2.21 13

25%II0I 6.9 2.9 4144 1.67 16 0.70 16

75%III0 26 23.5 5605 4.64 3 4.19 1

50%III0 23.9 20.8 5368 4.45 6 3.87 2

25%III0 18.6 14.2 5131 3.63 8 2.77 9

CWPt = crop water productivity of onion interms of total bulbyield, CWPm = crop water productivity of onion interms ofmarketable yield; I indicates full irrigation or the throughoutdeficit amount of water, 0 indicates the deficit amount of water, andits position indicates the stage in which the treatment applied.

cxxxvii

Chapter 5. Conclusion and

Recommendations

5.1. Conclusion

Scarcity of water is the most severe constraint for the

development of agriculture in arid and semi-arid areas. Under

these conditions along with the construction and development of

irrigation dams, different water harvesting structures, springs

and diversions, the need to use the available water economically

and efficiently using appropriate irrigation systems and

management is unquestionable. Based on the actual crop need, the

irrigation management has to be improved so that the water

supply to the crop can be reduced while still achieving high

yield. Therefore, this study was aimed to investigate whether

there is an option to conserve and economize the limited

available water through application of deficit irrigation as one

of water management alternative approaches and also to

cxxxviii

investigate the sensitive onion developmental stage for the

water deficit and come up with the following conclusions.

The very high significant effect (P < 0.001) of amount of

irrigation water application either throughout the developmental

stages or at specific developmental stage of onion on its bulb

yield and yield components implies that the crop is sensitive

enough to detect the moisture stress. In all cases application

of full irrigation throughout the crop developmental stages

resulted in the highest yield and yield components. However, 25%

water deficit application throughout the crop developmental

stages or only at establishment or ripening stages can be an

option, because, the yield increment in full irrigation is less

compared to the amount of yield that can be produced by the

saved water obtained from imposing the crop for 25% deficit

irrigation at the establishment or ripening stage as well as

throughout the crop phenological stages. When water stress is

imposed at the establishment stage; high yields of onion could

easily be sustained provided adequate watering conditions take

place during the rest of the growing season. It has also been

observed that, limited effect on yield resulted from water

cxxxix

deficit applied during the ripening stage. Water deficit at the

establishment and ripening stage of the crop also has less

effect on bulb diameter and bulb sizes relative to the effect of

water deficit created on the other two stages. Meeting the full

water requirement during the two extreme /establishment and

ripening/ stages is not advisable. Moreover, withholding 50% to

25% irrigation water application at the maturity/ripening stage

increase marketability of onion through its effect on decreasing

unmarketable yield components like decay, bolt, and split.

The most critical period for irrigation was the bulbification

stage. This period coincides with the highest water requirement

and the crop cannot withstand water deficit without substantial

reduction on yield. Next to the bulbification stage, water

stress at the vegetative development stage also highly affects

bulb yield and yield components of onion. This period is the

most critical period for the growth of yield contributing plant

components like plant height and leaf number. The height and

leaf number of onion strongly affected when deficit water is

applied at the vegetative development of the crop. This in turn

has significant effect on bulb yield of onion. 75% deficit

cxl

irrigation throughout the growing season or only at the

bulbification stage results the highest yield and yield

component reduction per unit of water deficit. It increases

number of small bulbs per hectare and unmarketable bulbs, too.

From the results of this experiment it is possible to conclude

that application of not more than 50% deficit irrigation at the

ripening stage can increase harvest index of onion. As compared

to the full irrigation water application, 75% irrigation water

application throughout the crop developmental stages increase

the harvest index of the crop by 7.07%. Whereas, the minimum

harvest index (52%) was obtained from the treatment that has got

only 25% of the full irrigation. The increased harvest index due

to reducing the amount of irrigation water application late in

ripening stage of onion might be due to accelerated movement of

photosyntates from the neck and leaves of onion to the loading

sites/bulbs/.

Deficit irrigation applications increased crop water

productivity from a minimum of 2.2% to a maximum of 6.5%

compared with the optimum application. But incase of application

cxli

of 75% deficit at bulbification stage, development stage or

throughout the crop growth stages the crop water productivity

value was the lowest, which showed that the amount of saved

water did not, compensate the amount of the yield loss. The

highest crop water productivity in terms of total bulb yield was

obtained from the 25% deficit irrigation water application (4.77

kg/m3). The saved water from such irrigation scheduling can

produce more bulb yield than the loss. This leads to the idea

that increasing the irrigated area with the saved water would

compensate for any yield loss. Therefore, proper application of

deficit irrigation practices can generate significant savings in

irrigation water allocation. Application of 50% to 25% deficit

irrigation late in the ripening stage would increase the water

productivity for marketable yield over the full irrigation. This

might be through the increasing of quality characters and or

through reducing unmarketable bulb yield components.

5.2 Recommendations

According to the finding from one season study the following

recommendations can be made:

cxlii

The most critical period for irrigation is the

bulbification stage followed by vegetative development

stage. Stressing onion at these stages should be avoided.

However, if water stress is unavoidable at these stages, it

is better to stress the crop 25% of the full irrigation

than 75% of the full irrigation. Application of deficit

irrigation either at the establishment or ripening stage is

good option to save water without significant bulb yield

reduction. Particularly, 50% to 25% deficit irrigation late

in the ripening stage can increases marketable bulb yield.

Either at specific growth stages or throughout the crop

growth stages the amount of irrigation water should not go

below 50% of the full irrigation water application.

In water scarcity areas application of 25% deficit

irrigation is a good option to increase productivity of

water and/or to introduce additional irrigable land with

the saved water.

This research was conducted on onion, which is one of the

sensitive crops to water stress. However, it showed

cxliii

promising upshot to save water without significant yield

reduction. Therefore, further research should be conducted

on such deficit irrigation practice to save even more water

from other crops with insignificant yield reduction.

When there is lack of long term climatic data of the area

and ETo calculator software to estimate the amount of

irrigation water, pan evaporation method can be used as the

best option for irrigation scheduling.

However, the result is limited to one season and location.

Hence, research should be done over season and location to

establish the optimum irrigation amount for optimum bulb

yield and the sensitive developmental stage of onion so as

to improve the productivity of water in the study area.

Moreover, future researches should comprise the effect of

irrigation amounts to onion dry matter weight, shelf life

and quality aspects like nutrition content and pungency.

cxliv

Farmers and extension workers in the study area have little

knowledge on deficit irrigation practices. Therefore,

creating and enhancing awareness should be done. Every

concerned body should give due attention for the water

management aspect along with the started effort for

construction and development of irrigation water sources.

cxlv

References

AGWARDO. 2010. Antsokia Gemza Woreda Agricultural and Rural

Development Office, Annual report [Unpublished], Mekoy.

Al-Harbi, R. 2002. Effect of Irrigation Regimes on Growth and

Yield of Onion (Allium cepa L.) Plant Production Department,

College of Agriculture, King Saud University, Riyadh, Saudi

Arabia. J. King Saud Univ. Agric. Sci. (1), pp. 1-11.

Allen, R., Pereira, L., Raes, D. and Smith, M. 1998. Crop

Evapotranspiration Guidelines for Computing Crop Water

Requirements. Irrigation,and Drainage Paper No. 56, Food,

Agricultural Organization, United Nations, Rome, Italy.

Amarasiri, S. 1990. Phosphorus management in intensive vegetable

cultivetion, International Rice Research Institute, Manila,

Philippine.

ARARI (Amhara Region Agricultural Research Institute). 2008.

Determination of optimum irrigation scheduling. In: Yihenew

G/Selassie (ed). Proceedings of the 2nd Annual Regional Conference on

Complete Natural Resource Management Research Activities (18-19 Sep2007)

Amhara Regional Agricultural Research Institute, Bahr Dar.

cxlvi

Asseng, S., Ritch, T., Sucker, T., and Robertson,J. 1998. Root

growth and water uptake during water deficit and recovering

in wheat. Plant and soil 201:265-273.

AVRDC (Asian Vegetable Research and Development Center). 2001.

Onion cultivation and seed production guidline, Shanhua,

Taiwan. Pp.151.

Ayas, S. and Cigdem, D. 2009. Deficit irrigation effects on

onion(Allium cepa L.E.T.Grano 502) yield in untreated green

house condition. Journal of Food, Agriculture and Environment, 7(3&4)

Pp. 239-243.

Bakker, M., Raine, R., and Robertson, M. 1999. A Preliminary

Investigation of Alternate Furrow Irrigation for Sugar Cane

Production. [online] http://www.usq.edu.au/users/raine/index

fiels/ASSCT /pdf. [accessed on 24,May,2009].

Bazza, M., and Tayaa, M. 1999. Contribution to improve sugar

beet deficit-irrigation. In: C. Kirda,P. Moutonnet, C. Hera &

D.R. Nielsen, (eds). Crop yield response to deficit irrigation,

Dordrecht, The Netherlands, Kluwer Academic Publishers.

Biswas K., Sarker, K., Mazharul, A., Islam, M., Bhuiyan, K. and

Kundu, B. 2003. Effect of Irrigation on Onion Production.

Irrigation and Water Management Division, Bangladesh

cxlvii

Agricultural Research Institute, Joydebpur, Gazipur 1701,

Bangladesh. Pakistan Journal of Biological Sciences 6 (20): 1725-1728.

Biswas, K., Khair, A., Sarker, P. and Alom, M. 2010. Yield and

Storability of Onion (Allium cepa L.) as Affected by

Varying Levels of Irrigation. Bangladesh J. Agril. Res. 35(2):

247-255.

Boyhan, G., Grandberry, D. and Kelley, T. 2001. Onion Production

Guide. Cooprative Extention Service. The University of

Georgia, Collage of Agricultural & Environmental Sciences.

Brewster, J. 2008. Onions and other vegetable Alliums. 2nd ed. CAB

International, Wallingford, UK. [onlone]

http://books.google.com.et/books?id [accessed on 05 Nov,

2010]

Brewster, L. and Rabinowitch, D. 1990. Onions and Allied Crops:

Botany, Physiology and Genetics. CRS Press. USA. p 320.

Brouwer, C and Prins K. 1989. Irrigation water management:

Irrigation scheduling. Training manual No. 4. Food and

Agricultural Organization of the United Nation, Rome,

Itally.

cxlviii

http://books.google.com.et/books?id

CSA (Ethiopian National Central Statistics). 1999. Statistical

Abstract, Addis Ababa, Ethiopia.

CSA (Ethiopian National Central Statistics). 2009. Agricultural

sample survey, Report on area and Production of crops (Peasant

holdings, Meher season), Addis Ababa, Ethiopia.

Currah, L. and Proctor, F. 1990. Onion in Tropical Regions. Natural

Resources Institute Bulletin No. 35.

David, G., Tolt, F., Scott, K., Mohan, H., Pappu, R. and

Schwartz, F. 2006. Iris yellow spot virus: An emerging

threat to onion bulb and seed production. The American

Phytopathological Society. 90:12.

Decoteau, R. 2000. Vegetable crops practice, Hall INC, New Jersy. Pp

326-327.

Doorenbos, J., Kassam, A., Bentvelsen, C., and Uittenbogaard,

G. 1979. Yield response to water. FAO Irrigation and Drainage

Paper No. 33, FAO, Rome, Italy. P 193.

Dragland, S. 1974. Nitrogen and water requirements in onions.

Forsk Frs. Landbrkt. pp. 26-93.

Drinkwater, W. and Janes, B. 1955. Effect of Irrigation and Soil

water on Maturity, Yield and Storage of two Onion hybrids.

American Society of Horticultural Sciences, 66: 267-279.

cxlix

Eck, V., Mathers, C., Musick, T., 1987. Plant water stress at

various growth stages and growth and yield of soybean. Field

Crop Res. 17, 1–16.

Elliades, G., 1988. Irrigation of greenhouse-grown cucumbers. J.

Hort. Sci. 63 2, pp. 235–239.

Ells, E., McSay, E., Soltanpour, N., Schweissing, C., Bartolo,

E. and Kruse, G. 1993. Onion irrigation and Nitrogen

leaching in the Arkansas Valley of Colorado. Hort. Tech. 32,

pp. 184–187.

Englsih, J., Music, T., Murty, N. 1990. Deficit irrigation. In:

Hoffman, J., Howell, A., Solomon, H. (Eds.), Management of

Farm Irrigation Systems. ASAE Monograph, Michigan, pp. 631–663.

Enyew, A., Lakachew, M and Abedin, M. 2007. Farmers Innovations

in Agricultural Water Management: Traditional irrigation

practices in Amhara Region, Amhara Region Agricultural

Institute, Ethiopia. In: Yihenew G/Selassie(ed). 2008.

Proceeding of the 2nd Annual Regional Conference on Compeleted Natural

Resource Management Research Activities (18-19 Sept, 2007). Amhara

Regional Agricultural Research Institute, Sep 2008. Bahir

Dar, Ethiopia.

cl

Evans, T. 1993. Crop Evolution, Adaptation and Yield, Cambridge

University Press Cambridge. p 500.

FAO (Food and Agricultural Organization of the United Nations).

2002. Deficit irrigation practice, Water Reports 22, Rome.


1996. Agriculture and Food Security, World Food Summit,

November 1996, Rome.


1997. Irrigation Potential in Africa: A Basin Approach, FAO

Land and Water bulletin 4. Rome, Italy.

FAO (United Nations Food and Agriculture Organization). 2007.

Statistical database, FAOStat [online]

http://faostat.fao.org/site/340/default.aspx [Date accessed

19, Oct, 2010].

Farre, I., Faci J. 2006. Comparative response of maize (Zea mays

L.) and sorghum (Sorghum bicolor L. Moench) to deficit

irrigation in a Mediterranean environment, Zaragoza, Spain.

Agricultural water management, (83) Pp.135 – 143.[online]

www.sciencedirect.com [accessed on 23, May,2009].

Faten, A., Shaheen , M., Fatma, R and. Magda, H. 2010.

Influence of Irrigation Intervals and Potassium

cli

http://www.sciencedirect.com/

http://faostat.fao.org/site/340/default.aspx

Fertilization on Productivity and Quality of Onion Plant,

NRC, Dokki, Cairo, EGYPT. International Journal of Academic Research.

2 (1).

Flip, G. 2003. Irrigation water quality standards and salinity

management strategies, The Texas A&M University stream.

Geremew, A., Teshome A., Kasaye T. and Amenti C. 2010. Effect

of intra-row spacing on yield of three onion (Allium cepa

l.) varieties at Adami Tulu agricultural research center

(mid rift valley of Ethiopia) Adami Tulu Agricultural

Research Center, Ethiopia. Journal of Horticulture and Forestry. 2(1)

pp. 007-011 [online] http://www.academicjournals.org/jhf

(accessed on 25 Oct,2010)

Getaneh, Y. 2002. Constraint analysis of small scale irrigation

schemes in Amhara and Tigray Regions. FAO’s Special

Programme for Food and Production (SPFP), Addis Ababa,

Ethiopia.

Gomie, A., Mohamed,K., El- Aref, O. and Massoud, M. 2000.

Studies on Some Egyptian Onion varieties under Upper Egypt

conditions: Effect of Soil Moisture Content on Storability

of Some Egyptian Onion Genotypes, Assiut Journal of Agricultural

Sciences. 31(5) Pp.129-136.

clii

Goodwin, I. and Boland, M. 2000. Scheduling deficit irrigation

of fruit trees for optimizing water use efficiency,

Department of Natural Resources and Environment, Institute

of Sustainable Irrigated Agriculture, Tatura, Australia.

In:Deficit irrigation practice, Water Reports 22, Rome.

Hanson B., May D., Voss R., Cantwell M., and Rice R. 2003.

Response of garlic to irrigation water. Agricultural water

management 58 Pp. 29-43.

Hegde, M. 1986. Effect of irrigation regimes on dry matter

production, yield, nutrient uptake and water use of onion.

Indian J. Agronomy, 31 Pp. 343-348.

Henry, E., Igbadun, Mahoo, H., Andrew, R., and Baadar A. 2004.

Productivity of water and economic benefit associated with

deficit irrigation scheduling in maize. Sokoin University of

Agriculture, Morogo Tanzania. [online]

www.iwmi.cgiar.org/Africa/files (Accessed on 12 Sep, 2009).

Heping, Z. 2003. Water Productivity. [online]

www.iwmi.cgiar.org//pubs/book/CA-CBI-series/ (Accessed on 12

Feb, 2010).

Jackson, T., Agegnehu, H., Brunco, W., Haussler, S., Proctor F.

and Semungus, H. and Zimmermann, A. 1985. A practical guide

cliii

http://www.iwmi.cgiar.org//pubs/book/CA-CBI-series/

http://www.iwmi.cgiar.org/Africa/files

to Horticulture in Ethiopia. Ministry of state Farm

Development, Horticultural Department A.A, Ethiopia. p59.

Kadayifcia, A., Tuylua, G., Ucarb, Y., Cakmakc, B. 2005. Crop

water use of onion (Allium cepa L.) in Turkey, Agricultural

Water Management, 2005 (72) Pp. 59–68. [online]

www.sciencedirect.com [accessed on 17Apr, 2009]

Kassam, A., and Smith, M. 2001. FAO Methodologies on Crop Water

Use and Crop Water Productivity, Paper no. CWP-M07, ROME.

Khan H., Imran, M and Chattha, T. 2005. Effect of Irrigation

Intervals on Growth and Yield of Onion Varieties Swat–1 and

Phulkara. Journal of Applied Sciences Research.1(2) Pp. 112-116.

Kirda, C. 2000. Deficit irrigation scheduling based on plant

growth stages showing water stress tolerance. Cukuroya

University Adana, Turkey. In: Deficit irrigation practice. Water

reports No 22. Food and Agricultural Organization of the

United Nations, Rome, Italy.

Kumar, S., Imtiyaz, M., Kumar, A. and Singh, R. 2007. Response

of onion (Allium cepa L.) to different levels of irrigation

water, India. Agricultural Water Management 89, (1-2), Pp 161-

166. [Online]

cliv

http://www.sciencedirect.com/science/journal/037883774

[accessed on Oct, 2010].

Lemma, D. and Herath, E. 1994. Agronomic Studies on Allium. In:

Lemma, D. and E. Herath(eds).1994. Proceedings of the second

National Horticultural Workshop of Ethiopia. pp139-146

Lemma, D., and Shimelis, A. 2003. Research Experience in Onion

Production, EARO, Report No. 55. Addis Ababa. Ethiopia.

Majumdar, K. 2000. Irrigation water management principles and

practice, Printice Hal of India Private Limited, New Delhi,

India.

Maldonado, I., Quezada, C., León L. and Márquez, L. 2006.

Irrigation scheduling in the sugar beet by pan evaporation

and the Penman-Monteith equation. Cien. Inv. Agr. 33(3), Pp.201-

210.

MARC (Melkasa Agricultural Research Center). 2003. Progress

report for 1995-2003. Ethiopian Agricultural Research

Organization, Ethiopia.

Mart´ın de Santa Olalla, J., Lopez, R., Dom´ınguez, A. 2004.

Production and quality of the onion crop (Allium cepa L.)

cultivated under controlled deficit irrigation conditions in

a semi-arid climate, Agricultural Water Management 68, Pp. 77–89.

clv

Mintesinot B., Verplancke H., Van Ranst E., and Mitiku H. 2004.

Examining traditional irrigation methods, irrigation

scheduling and alternative furrow irrigation on vertisols in

Northern Ethiopia. Agricultural water management. 64 Pp.17-24

Mintesnot, B. 2002. Assesment and optimization of traditional

irrigation of vertisols in Northen Ethiopia. A case study at

Gumselasa microdam using maize as indicator crop. Ph.D

Thesis. Ghent University Belgium.

MoFED(Ministry of Finance and Economic Development). 2007.

Annual Report on Macroeconomic Developments for 2006/07,

Addis Abeba, Ethiopia.

Mohammed, S.J. 2004. Studies on management strategies for bulb

and seed production of different varieties of onion (Allium

cepa L.) Faculty of Agriculture, Gomal University, Dera

Ismail Khan.

Mondal, M., Brewster, J., Morris J. and Butter, A. 1986. Bulb

development in onion - Effect of plant density and sowing

date in field conditions. Annals of Botany, 58:187-195.

Moutonet, P. 2000. Yield response factors of field crops to

deficit irrigation. In: Deficit irrigation practice. Water reports.No.

22. IAEA Division/joint FAO, Vienna Austria.

clvi

Mumns, R., John, L., Peter, C., Ping-Hua, H., Schuppler, U.

1998. Effect of water Stress on cell division and Cdc2-Like

cell cycle kinase activity in Wheat leaves. Plant Physiol. 117

Pp. 667-678.

Nonnecke, I. 1989. Vegetables Production. Van Nostrand Reinhold

Library of Congress. New York, USA.

Orta, A.H. and Şener, M. 2001. A study on irrigation scheduling

of onion (Allium cepa L.) in Turkey. Journal of Biological

Sciences, 1 (8): 735-736.

Orta, A. H. and Ener, M. 2001. Irrigation scheduling of onion in

Tekirdag province of Turkey. Jour. Appl. Hort. 3(2)75-77.

Ouda, A.S, Rashad A.E., and Mouhamed A. S. 2010. Using Yield-

Stress Model to Predict the Impact of Deficit Irrigation on

Onion Yield. Agricultural Research Center, 14th

International Water Technology Conference, Cairo, Egypt.

Oweis, T., Hachum, A., and Kilne, J. 1999. Water Harvesting and

Supplemental Irrigation for Improved Water use Efficiency in

Dry Areas. SWIM Paper No. 7. International Water Management

Institute,

Pandey, K., Maranville, W. and Chetima, M. 2001.Tropical wheat

response to irrigation and Nitrogen in Sahelian environment:

clvii

Biomass accumulation, nitrogen uptake and water extraction,

European Journal of Agronomy 15 Pp. 107-118.

Pathak, S. 1994. Allium for the tropics: Problems and AVRDC

strategy. International Symposium on Allium for Tropics. ISHS Acta

Horticulture No 358.

Payero, O., Steven, R., Suat, I. and David, T. 2006. Yield

response of corn to deficit irrigation in a semiarid

climate, University of Nebraska Agricultural Research

Division, Lincoln. Agricultural water management 84 Pp. 101-112

[online] www.sciencedirect.com (Accessed on 12Sep, 2010)

Rabinowitch, D. and Currah, L. 2002. Allium Crop Science: Recent

Advances. CABI Publishing. United Kingdom. p 585.

Rademaker, M. 2009. Onions. [online]

http://dermnetnz.org/dermatitis/plants/onion.html (accessed

on 23 Oct, 2010)

Rajasekaran, R. and Blake, J. 1999. New plant growth regulators

protect photosynthesis and enhance growth under drought of

Jack Pine seedlings. Plant Growth Regul. 38, Pp.1-7

Ronald, V., Mike, M., Kent, B., Keith, S and Evan, M. 1999.

Onion Seed production in California. University of

clviii

California, Division of Agriculture and Natural Resources.

Rosenthal, F., Arkin, F., Shouse, J., and Jordan, R. 1987.

Water deficit effects on transpiration and leaf growth.

Agronomy Journal 79, Pp 156-169.

Sadeghipour, O. 2008. Effect of withholding irrigation at

different growth stages on yield and yield conponents of

Mungbean (Vigna radiate L. Wilczek) Varieties. American-Eurasian J.

Agric.& Environ.Scie., 4(5) Pp 590-594.

Salkini, B., and Oweis, T. 1993. Optimizing ground water use for

supplemental irrigation of wheat production in Syria. Farm

resource management programme, Annual report ICARDA, In:

ICARDA(International Center for Agricultural Research in Dry

land Areas) and ESCWA (Economics and Social Commission for

Western Asia).2003. Enhancing agricultural productivity through on –farm

water use efficiency: An empirical case study of wheat production in Iraq. New

York, pp. 6-9.

Saleth, M. 1996. Water Institutions in India: Economics, Law and

Policy, Common wealth Publishers, New Delhi.

Samson B, and Ketema T. 2007. Regulated deficit irrigation

scheduling of onion in semiarid region of Ethiopia.

Agricultural water management, 89 Pp 148 – 152.

clix

Shani, U. and Dudley, M. 2001. Field studies of crop response to

water and salt stress. Soil Sci.Soc. AM.J., 56. Pp 263-285.

Shaozhang, K. 2004. Regulated deficit irrigation and alternate

partial root zone irrigation. Concepts, principles,

progresses and applications. Efficient irrigation technology

and management. International TCDC training courses on

efficient irrigation technology and management. Beijing.

SARC(Sirinka Agricultural Research Center). 2003. Research

outputs, Recommended and Released Technologies of Sirinka

Agricultural Research Center, Sirinka.P 38.

Shock ,C., Feibert, E. and Lamont S. 2003. Effect of short-

duration water stress on onion single centerdness and

translucent scale, Malheur Experiment Station Oregon State

University Ontario.

Shock, C., Feibert, G. and Saunders, L. 2000. Irrigation

criteria for drip-irrigated onions, Hortic. Sci. 35, Pp. 63–66.

Shock, C., and Feibert, E. 2006. Onion yield and quality

affected by soil water potential as irrigation threshold.

HortScience, 33,(7) Pp. 1188-1191.

Shock, C., Feibert,E., Klauzer, J. and Jensen, L. 2010.

Successful onion irrigation scheduling, Oregon State

clx

University Extension Service, Ontario.

Signh, R. and Aldefer, R. 1996. Effect of soil moisture stress

at different periods of some vegetable crops. Soil Science

journal, 101(1) Pp. 69-80.

Sileshi, B., Merrey, J., Kamara, B., Van Koppen, B., Penning de

Vries, F., Boelee, E., Makombe, G. 2005. Experiences and

opportunities for promoting small–scale/micro irrigation and

rainwater harvesting for food security in Ethiopia. Colombo,

Sri Lanka: International Water Management Institute. P. 43.

Sileshi, B., Aster, D., Mekonen,L., Loiskandl, M., Mekonene, A.,

Tena, A. 2007. Water Resources and Irrigation Development in Ethiopia.

Colombo, Sri Lanka: International Water Management

Institute. Pp. 6-38.

Sinclaire, P. 1982. Onion varieties for late sowing NSW Dept. of

Agric.,Yanco Agric. Institute Belletin, Yanco 3 Pp 16-18

In: International Symposium on Allium for the Tropics. Acta

Horticulture, 350:Pp. 253-357

Smith, M., Kivumbi, D. and Heng, L. 2000. Use of the FAO CROPWAT

Model in deficit irrigation studies, Vienna, Austria.

Deficit Irrigation Practice Water Reports No 22.

clxi

Steduto, P. 1996. Water use efficiency. In: Pereira, L.S.,

Feddes, R.A., Gilley, J.R., Lesaffre, B. (Eds.) Sustainability

of Irrigated Agriculture, NATA ASI Series E: Applied Sciences, vol.

312. Kluwer Academic Publishers, London, UK . In: Mart´ın de

Santa Olalla, J., Lopez, R., Dom´ınguez, A. 2004.

Production and quality of the onion crop (Allium cepa L.)

cultivated under controlled deficit irrigation conditions in

a semi-arid climate, Agricultural Water Management 68, Pp. 77–89.

Stegman, C., Schatz, G., and Gardner, C. 1990. Yield

sensitivities of short season soybeans to irrigation

management. Irrigation Science. 11, Pp 111-119.

Teixeira, G., Sinclair, F., Huwe, B., and Schroth, G. 2003.

Soil water. In: Schroth, G. and F.L Sinclair (eds.), Trees,

Crops and Soil Fertility Concepts and Research Methods. Cabi Publishing,

UK.

Tibebe, E. and Siobhan, O. 2000. Silent Revolution: The role of

Community Development in Reducing the Demand for Small Arms,

Working No.3. World Vision Publications, Monrovia, USA.

Tindal, H.D. 1983. Vegetable in the tropics. The Macmillan Press

Limited. London and Basingstoke.

clxii

Urrea, R., Cortes, C., Mart´ın de Santa Olalla, F. 2003.

Production of garlic (Allium sativum L.) under controlled

deficit irrigation in a semiarid climate. Agricultural Water

Management, 59 Pp. 155-163.

Van Eeden, F. and Myburgh, J. 1971. Irrigation trials with onions.

Agroplantae, 3. Pp.57-62.

Von Braun, J. 1991. A Policy Agenda for Famine Prevention in

Africa. Food Policy Technology and Research in Irrigation

and Drainage (IPTRID). Rome: Food and Agricultural

Organization of the United Nations. Statement No. 13,

International Food Policy Research Institutes.

Waren, A. and M, Khogali. 1992. Assessment of Desertification

and Drought in the Sudano-Sahellan Region 1985-1991, UNSO,

New York.

World Bank. 2004. Opportunities and Challenges for Development

of High Value Agricultural Exports in Ethiopia [online]

http://lnweb18.worldbank.org/ESSD/ardext.nsf. [Date of

accessed Dec, 2009]

WVE (World Vision Ethiopia). 2009. World Vision Ethiopia

Antsokia Gemza Area Development Programme unpublished

clxiii

http://lnweb18.worldbank.org/ESSD/ardext.nsf.%20%20%5BDate

documented on developed and constructed irrigation schemes

by WVE, Mekoy, Ethiopia.

Yenesew, M. and Ketema, T. 2009. Yield and Water Use Efficiency

of Deficit Irrigated Maize in a Semi arid region of

Ethiopia. African Journal of food Agriculture nutrition and Development,

9(8)

Yonas, G., Zainul, A., Gizaw, D., Tegenu,A., and Enyew, A. 2007.

Documentation of successful traditional farmers’ practices

and innovations in agricultural water management in Amhara

Region. In:Yihenew G/Selassie(ed). 2008. Proceeding of the 2nd

Annual Regional Conference on Compeleted Natural Resource Management

Research Activities (18-19 Sept, 2007). Amhara Regional

Agricultural Research Institute, Sep 2008. Bahir Dar,

Ethiopia.

Zilberman D. and Schoengold K. (nd). Water and development: the

importance of irrigation in developing countries [online]

pdf. [Accessed on 18 Oct, 2010].

Zwart, S. and Bastiaanssen, W. 2004. Review of Measured Crop

Water Productivity Values for Irrigated Wheat, Rice, Cotton

and Maize. Agricultural Water Management. 6(9). Pp. 115–133.

clxiv

Appendices

Appendix A: Meteorological data

Table A.1: Monthly annual rainfall (mm) of the experimental area

(Majettie) from 1980-2008. (Source: National Meteorological Agency,

Kombolcha Sub branch, 2009)

Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annu

al

1980 33.2 69.2 16.2 83.

0

8.8 15.

7

202

.9

302

.3

58.

0

38.

8

36.

2

0.0 864.

3

1981 0.0 10.8 199.

6

79.

2

3.2 0.0 307

.4

314

.0

132

.7

49.

8

0.0 2.5 1099

.2

1982 17.6 43.1 51.3 36.

5

83.

1

0.0 102

.7

200

.6

124

.3

109

.1

96.

8

40.

1

905.

2

1983 40.2 61.0 39.1 85.

0

65.

0

20.

1

191

.0

238

.1

22.

0

69.

6

0.0 2.5 833.

6

1984 0.0 0.0 47.8 53.

5

163

.2

29.

2

113

.2

18.

7

109

.4

0.0 2.3 96.

5

633.

8

1985 11.2 0.0 37.5 120

.6

124

.2

0.0 223

.9

384

.5

100

.6

2.5 0.0 13.

7

1018

.7

1986 0.0 59.0 85.5 96.

0

31.

6

75.

3

129

.8

249

.9

153

.3

8.4 0.0 11.

0

899.

8

1987 0.0 16.0 55.0 121

.5

87.

0

0.0 24.

7

397

.2

47.

5

45.

6

0.0 38.

7

833.

2

clxv

1988 33.7 142.

0

36.8 88.

0

9.2 10.

8

199

.8

472

.5

117

.8

14.

6

0.0 0.0 1125

.2

1989 11.8 71.8 54.0 120

.2

20.

1

25.

1

158

.7

270

.6

160

.8

37.

8

0.0 88.

5

1019

.4

1990 48.3 144.

9

134.

1

141

.3

0.0 0.0 203

.7

182

.0

157

.9

6.3 0.0 0.0 1018

.5

1991 8.6 114.

1

67.0 36.

2

15.

5

8.1 224

.4

169

.1

123

.1

35.

8

0.0 18.

5

820.

4

1992 96.4 39.9 35.7 67.

8

30.

2

51.

4

163

.8

234

.6

88.

7

173

.1

101

.7

26.

2

1109

.5

1993 126.

5

48.6 8.0 86.

0

189

.7

5.2 205

.3

166

.1

99.

7

66.

7

0.0 0.0 1001

.8

1994 0.0 4.6 43.8 40.

6

12.

3

23.

6

240

.7

412

.9

160

.7

7.1 50.

7

2.2 999.

2

1995 0.0 88.3 46.8 150

.7

71.

5

54.

0

354

.6

355

.6

130

.8

26.

1

0.0 74.

9

1353

.3

1996 41.2 0.0 163.

3

120

.8

120

.4

57.

0

299

.3

379

.0

101

.9

8.9 53.

1

0.0 1344

.9

1997 41.0 0.0 129.

7

69.

4

7.9 53.

6

222

.2

266

.6

61.

7

270

.3

143

.9

0.0 1266

.3

1998 108.

0

91.8 59.7 121

.6

74.

3

9.0 464

.8

373

.8

127

.2

62.

7

2.3 0.0 1495

.2

1999 94.9 0.3 35.6 91.

3

22.

9

10.

0

438

.5

504

.5

148

.5

261

.1

5.6 0.3 1613

.5

2000 0.0 0.0 1.2 85.

1

77.

5

12.

2

318

.0

401

.0

131

.1

51.

3

103

.3

27.

5

1208

.2

2001 7.6 2.1 45.0 14.

4

96.

6

11.

0

450

.8

240

.3

105

.9

11.

2

8.0 1.8 994.

7

2002 106.

4

6.8 60.4 74.

0

31.

4

26.

8

247

.5

311

.2

99.

4

7.4 2.6 163

.1

1137

.0

2003 63.2 44.1 82.7 98.

8

3.1 20.

8

254

.1

250

.2

186

.1

3.0 3.9 61.

1

1071

.1

2004 0.0 69.9 0.0 97.

6

5.9 47.

5

199

.9

259

.4

118

.9

40.

4

59.

1

29.

2

927.

8

2005 53.3 0.0 144. 98. 113 40. 208 228 191 9.5 62. 0.0 1150

clxvi

4 0 .9 3 .6 .4 .9 4 .7

2006 56.3 10.7 55.4 15.

0

9.0 36.

4

340

.0

508

.3

107

.3

34.

9

0.0 38.

0

1211

.3

2007 20.9 20.1 72.9 86.

6

79.

4

31.

4

302

.9

438

.1

156

.9

22.

6

12.

0

0.0 1243

.8

2008 50.0 0.0 0.0 59.

6

28.

3

27.

9

225

.8

254

.5

96.

7

59.

7

153

.0

0.0 955.

5

Averag

e

36.9 40.0 62.4 84.

1

54.

7

24.

2

242

.0

302

.9

118

.0

52.

9

30.

9

25.

4

1074

.3

Table A.2. Monthly average maximum temperature (oC) of Majettie

(1999-2008) (Source: National Meteorological Agency, Kombolcha Sub

branch, 2009)

Ja

n Feb

Ma

r

Ap

r May

Ju

n

Ju

l

Au

g

Se

p Oct

No

v Dec

1999

25

.8

29.

1

27

.0

31

.3

32.

0

33

.2

28

.5

28

.4

28

.2

26.

7

26

.3

25.

3

2000

27

.0

28.

3

29

.5

29

.7

31.

1

33

.4

30

.1

27

.9

28

.0

27.

2

25

.8

25.

2

2001

23

.7

27.

5

26

.6

30

.3

31.

3

33

.2

29

.6

28

.1

28

.3

28.

7

26

.7

26.

7

2002

24

.7

27.

7

28

.6

29

.5

32.

5

33

.4

32

.1

29

.2

28

.5

29.

4

28

.1

24.

7

2003

24

.9

28.

2

29

.0

29

.1

32.

6

33

.2

30

.3

28

.2

29

.0

28.

7

27

.8

25.

7

2004

25

.1

26.

2

28

.4

28

.8

33.

0

32

.7

31

.2

29

.7

29

.0

27.

5

27

.3

25.

5

200525

.3

29.

7

28

.7

29

.1

29.

8

32

.2

29

.3

29

.0

28

.6

28.

0

27

.2

26.

5

clxvii

2006

26

.8

27.

3

28

.6

27

.8

31.

1

33

.1

29

.4

28

.0

28

.2

28.

0

27

.6

25.

3

2007

23

.9

26.

9

29

.2

29

.4

31.

8

31

.8

28

.8

28

.3

28

.5

27.

6

26

.8

26.

4

2008

26

.5

26.

6

30

.2

30

.3

31.

9

33

.1

30

.6

28

.8

28

.4

28.

1

25

.4

25.

1

Avera

ge

25

.4

27.

7

28

.6

29

.5

31.

7

32

.9

30

.0

28

.6

28

.5

28.

0

26

.9

25.

7

Table A.3. Monthly average minimum temperature (oC) of Majettie

(1999-2008) (Source: National Meteorological Agency Kombolcha Sub

branch, 2009)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

1999

11.

3

10.

4

14.

1

14.

6

16.

0

17.

1

15.

9

15.

4

14.

8

14.

2 9.9 9.8

2000

10.

3

10.

3

12.

5

14.

8

16.

2

17.

3

16.

5

16.

2

15.

6

13.

8

11.

7

11.

1

2001

11.

4

11.

8

15.

1

14.

9

16.

5

18.

5

16.

7

16.

6

15.

2

14.

4

11.

4

10.

6

2002

13.

6

12.

2

15.

7

15.

6

16.

1

18.

2

18.

1

16.

8

15.

9

13.

3

11.

3

15.

2

2003

12.

7

13.

8

14.

8

16.

1

16.

4

18.

1

17.

3

16.

6

16.

1

12.

4

12.

1

10.

4

2004

12.

1

12.

8

13.

7

16.

0

15.

2

17.

5

17.

0

16.

4

15.

2

12.

6

12.

0

12.

3

200512.

9

12.

7

15.

7

16.

0

17.

0

17.

2

17.

0

17.

1

15.

9

13.

1

11.

6 9.2

clxviii

2006

12.

3

14.

3

14.

9

15.

7

16.

3

17.

8

17.

5

16.

6

15.

7

14.

7

13.

2

14.

2

2007

13.

7

15.

0

14.

5

16.

4

17.

0

18.

2

16.

8

16.

5

15.

7

12.

7

11.

9 9.8

2008

12.

2

11.

7

11.

1

15.

8 18

18.

4

17.

7

16.

6

15.

5 14

11.

8

12.

4

Av.

12.

2

12.

5

14.

2

15.

6

16.

5

17.

8

17.

0

16.

5

15.

6

13.

5

11.

7

11.

5

Table A: 4. Monthly average winds speed (m/s) of the

experimental area from 2003-2007. (Source: National Meteorological

Agency Kombolcha Sub branch, 2009)


2003

0.7

9 1.08 1.06 0.83

1.0

2

8.1

5

3.4

6

2.6

9

0.6

8

0.7

7

1.2

5

0.9

1

2004

0.8

0 0.95 1.08 0.93

1.2

0

1.1

8

1.1

3

0.9

6

0.6

7

0.7

7

0.8

6

0.9

4

2005

0.8

9 1.41 1.19 1.10

1.0

2

1.3

0

1.0

3

0.9

9

0.7

8

0.8

9

1.0

7

1.1

4

2006

1.0

7 1.26 1.23 1.00

1.0

9

1.2

1

0.8

6

0.8

7

0.7

8

0.8

1

1.0

5

0.9

3

2007

0.9

5 1.11 1.25 1.03

2.0

4

1.0

5

1.0

0

0.9

2

0.7

6

0.9

8

1.0

2

1.0

7

Avera 0.9 1.16 1.16 0.98 1.2 2.5 1.5 1.2 0.7 0.8 1.0 1.0

clxix

ge 0 8 8 0 9 4 5 5 0

Table A: 5. Monthly average sunshine hours in the experimental

area from 2003-2007 (Source: National Meteorological Agency,

Kombolcha Sub branch, 2009)


2003 6.8 8.5 7.4 7.1

10.

3 7.4 6.1 7.0 5.4 9.5 8.9 8.3

2004 6.5 7.0 7.6 7.0

10.

0 6.9 5.0 7.3 6.0 8.6 9.4 6.7

2005 5.2 9.6 6.4 7.2 8.1 7.7 6.0 6.8 6.3 8.7 9.4

10.

2

2006 8.4 6.9 6.6 6.9 8.9 7.8 7.2 6.3 8.1 8.2 8.9 6.7

2007 5.9 6.8 8.0 8.2 9.0 7.3 6.4 7.4 8.2 9.7 8.9 9.2

Averag

e 6.5 7.8 7.2 7.3 9.3 7.4 6.1 7.0 6.8 9.0 9.1 8.2

Table A: 6. Monthly average relative humidity (%) of Majettie

from 2004-2007 (Source: National Meteorological

Agency, Kombolcha Sub branch, 2009)

Jan Feb Mar Apr May Jun

Ju

l Aug Sep Oct Nov Dec

2004 61 57 54 56 47 42 59 65 62 54 51 59

2005 64 45 58 55 57 40 60 62 63 52 50 45

2006 55 60 55 59 42 35 59 68 62 53 48 63

2007 65 59 49 54 42 43 67 67 63 50 51 50

clxx

Averag

e 61 55 54 56 47 40 61 66 63 52 50 54

clxxi

Table A.7. Summary of weather data and monthly ETo of Majettie

area

Country

Ethio

pia

Station

Majet

tie

Altitud

e 1652

Longitu

de

39.83o

E

Latitud

e

10.73o

N

Month

Min

Temp

Max

Temp

Humidi

ty Wind Sun Rad ETo

°C °C %

km/

day hours

MJ/m2/

day

mm/

day

January 12.2 25.4 61 78 6.5 16.9 3.24

Februar

y 12.5 27.7 55 100 7.8 20 4.06

March 14.2 28.6 54 100 7.2 20.2 4.33

April 15.6 29.5 56 85 7.3 20.8 4.41

May 16.5 31.7 47 111 9.3 23.4 5.24

June 17.8 32.9 40 223 7.4 20.2 6.2

July 17 30 61 130 6.1 18.4 4.45

August 16.5 28.6 66 111 7 20 4.37

Septemb

er 15.6 28.5 63 64 6.8 19.6 4.05

October 13.5 28 52 73 9 22 4.3

Novembe 11.7 26.9 50 91 9.1 20.7 4.02

clxxii

r

Decembe

r 11.5 25.6 54 86 8.2 18.7 3.53

Average 14.6 28.6 55 104 7.6 20.1 4.35

Table A.8. Rainfall amount (mm) during the experimentation from

Nov, 2009-May, 2010.

Months

Nov Dec Jan Feb Mar Apr May

1 0 0 3.2 0 0 0 0

2 0 0 9.2 0 3.6 0 0

3 0 0 0 0 0 0 0

clxxiii

4 0 0 0 0 0 0 0

5 0 0 0 0 6.6 3.5 0

6 0 0 0 4.2 4.6 0 0

7 0 0 0 0 0 9.5 0

8 0 0 0 0 0 0 2

9 0 0 0 0 0 0 2.8

10 0 2.5 0 0 0 0 3.1

11 0 12.4 0 7.8 0 4.6 0

12 0 0 0 0 0 2.4 0

13 0 13.5 0 0 0 0 9.7

14 0 0 0 1.2 0 0 0

15 0 0 0 0 0 0

16 0 0 0 0 0 0

17 0 0 0 0 0 12.2

18 0 0 0 0 0 0

19 0 1.7 0 0 0 0

20 0 10.8 0 0 0 0

21 0 0 0 0 0 0

22 0 0 0 0 0 4.4

23 0 2 0 0 0 0

24 0 4.1 0 0 0 0

25 0 0 0 0 0 6.4

26 0 0 0 4.2 0 0

27 0 2.2 0 1.5 0 0

28 2.7 0 0 0 0 0

29 1.7 0 0 0 0

30 7 0 0 0 0

31 0 0 0

Sum 11.4 49.2 12.4 18.9 14.8 43

clxxiv

Table A.9. Measured pan evaporation data (mm) during the

experimentation (Dec 2009-May, 2010)

Months

Dec Jan Feb Mar Apr May

1 9085.92 84.6 84.7 75.6 84.88 57.8

2 81.1 89.1 80 73.74 78.9 53.990

3 75.52 83.87 74.7 68.76 72.98 83.5

4 70 79.18 68.6 63.4 64.63 78

5 65.46 73.44 64.81 58.7 69.28 72.45

6 59.38 71.64 63.6 54.0890 62.93 67.8

7 53.83 65.64 59.47 85.2 66.38 62.5

8 49.6390 59.76 54.94 80.62 59.75 58.4

9 84.8 55.26 49.3490 74.84 54.390 55.590

10 83.3 50.0690 85.1 68.34 85.2 85.3

11 91.1 83.34 87.4 63.96 83.8 79.98

12 86.2 78.54 81.72 57.96 79.27 75.6

13 95.8 74.54 76.02 52.72 74.06 69.4

14 90 69.04 72.94 47.8990 69.14 65.4

15 84.5 64.04 66.16 89.6 64.57 58.3

16 79.6 58.54 60.55 83.46 58

17 74.990 51.28 55.44 77.02 68.87

18 85.79 46.890 50.6490 71.04 61.990

19 82.47 83.14 86.11 65.54 84.2

20 87.08 77.14 81.33 61.78 77.7

21 82.10 71.42 76.09 57.67 71.3

22 78.00 67.33 71 53.38 68.9

23 72.70 60.94 66.13 48.690 62.52

clxxv

24 72.82 54.06 60.26 84.84 55.52

25 65.18 47.1690 54.13 79.58 56.690

26 62.00 83.38 52.9690 74.94 84.8

27 62.9 76.38 85.8 70.05 78.4

28 57.87 71.3 81.5 64.94 74.76

29 52.5 65.65 63.28 68.72

30 47.690 61.91 57.73 62.91

31 85.48 56.2290 51.790

Superscript 90 indicates refilling of the pan to 90 mm

Appendix B: Irrigation related data

Table B.1. Comparison of the reference evapotranspiration ETo

by FAO Penman –Montheith model and Pan evaporation method.

Month Dec Stag

e

Kc K

pan

Pan

Evapn

Eto

Pan

Eto

PM

Etc

PM

Etc

Pan

Diff.

(PM-

Pan)

Coe

ff

Coe

f

mm/de mm/de mm/de mm/de mm/de

Feb 1 Init 0.7 0.7

5

44.46 33.35 34.14 23.90 23.34 0.56

Feb 2 Init 0.7 0.7

5

52.13 39.10 40.57 28.40 27.37 1.03

Feb 3 Deve 0.7

4

0.7

5

42.57 31.93 33.11 24.50 23.63 0.87

Mar 1 Deve 0.8

4

0.7

5

54.7 41.03 42.38 35.60 34.46 1.14

Mar 2 Deve 0.9

5

0.7

5

56.96 42.72 43.26 41.10 40.58 0.52

clxxvi

Mar 3 Mid 1.0

3

0.7

5

54.58 43.94 47.96 49.40 45.25 4.15

Apr 1 Mid 1.0

3

0.7

5

56.5 42.38 43.98 45.30 43.65 1.65

Apr 2 Mid 1.0

3

0.7

5

63.3 47.48 44.27 45.60 48.90 -3.30

Apr 3 Late 1.0

1

0.7

5

65.49 49.12 46.93 47.40 49.61 -2.21

May 1 Late 0.9

6

0.7

5

54.7 41.03 34.67 33.30 39.38 -6.08

Tota

l

545.3

9

412.0

8

411.2

7 374.5

376.1

7 -1.67

Evapn -evaporation, PM -Penman-Monteith method, Dec –decade, Diff -

difference.

Table B.2. Measured discharge and application time for single

(1.2m2) furrow of full irrigation

Date of irrigation Stage

Gr. Irr(mm)

Dischargel/s

Application duration per furrow (s)

7-Feb, 2010 Estabt 26.1 1.6 19.8

13-Feb, 2010 Estabt 27.5 1.5 22

19-Feb, 2010 Estabt 28.4 1.7 20.4

25-Feb, 2010

Veg.de

v 30.3 1.3 27.9

3-Mar, 2010

Veg.de

v 33.1 1.3 31.8

9-Mar, 2010

Veg.de

v 35.6 1.3 34.2

clxxvii

15-Mar, 2010

Veg.de

v 40.2 1.7 28.9

21-Mar, 2010

Veg.de

v 41.8 1.4 36.8

27-Mar, 2010 Bulbfn 44.9 1.7 32.3

2-Apr, 2010 Bulbfn 45.1 1.5 36.1

8-Apr, 2010 Bulbfn 45.3 1.5 36.2

14-Apr,

2010 Bulbfn 45.5 1.7 32.8

20-Apr, 2010 Bulbfn 45.6 1.4 40.1

26-Apr,2010 Ripen 47.4 1.5 37.9

2-May, 2010 Ripen 47.4 1.4 41.7

Table B.3. Date of irrigation and gross irrigation water amount

for each treatment in mm

Date of irrigation water application and stage of the crop

7-Feb

13-

Feb

19-Feb

25-Feb

3-Mar

9-Mar

15-Mar

21-Mar

27-Mar

2-Apr

8-Apr

14-Apr

20-Apr

26-Apr

2-May

7-May

Est

Est Est Dev Dev Dev Dev Dev

Bulb

Bulb

Bulb Bulb

Bulb Rip Rip End

Etc (mm)

15.7

16.5

17.1

18.2

19.9

21.3

24.1

25.1

26.9

27.0

27.2 27.3

27.4

28.4

28.5

Rf (mm)

4.2

7.8 1.2 0.0 9.3

11.2 0.0 0.0 0.0 0.0

13.0 7.0

12.2

10.8 0.0

Pe (mm)

0.0

0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 1.5 0.0 1.1 0.4 0.0

Net.Irr (mm)

15.7

16.5

17.1

18.2

19.9

20.7

24.1

25.1

26.9

27.0

25.7 27.3

26.3

28.0

28.5

Trts Gross Irrigation 100%IIII

26.1

27.5

28.4

30.3

33.1

35.6

40.2

41.8

44.9

45.1

45.3

45.5

45.6

47.4

47.4

75%IIII

19.6

20.6

21.3

22.7

24.8

26.7

30.2

31.4

33.7

33.8

34.0

34.1

34.2

35.6

35.6

50%IIII

13.1

13.8

14.2

15.2

16.6

17.8

20.1

20.9

22.5

22.6

22.7

22.8

22.8

23.7

23.7

25% 6. 6.9 7.1 7.6 8.3 8.9 10. 10. 11. 11. 11. 11. 11. 11. 11.

clxxviii

IIII 5 1 5 2 3 3 4 4 9 975%0III

19.6

20.6

21.3

30.3

33.1

35.6

40.2

41.8

44.9

45.1

45.3

45.5

45.6

47.4

47.4

50%0III

13.1

13.8

14.2

30.3

33.1

35.6

40.2

41.8

44.9

45.1

45.3

45.5

45.6

47.4

47.4

25%0III

6.5 6.9 7.1

30.3

33.1

35.6

40.2

41.8

44.9

45.1

45.3

45.5

45.6

47.4

47.4

75%I0II

26.1

27.5

28.4

22.7

24.8

26.7

30.2

31.4

44.9

45.1

45.3

45.5

45.6

47.4

47.4

50%I0II

26.1

27.5

28.4

15.2

16.6

17.8

20.1

20.9

44.9

45.1

45.3

45.5

45.6

47.4

47.4

25%I0II

26.1

27.5

28.4 7.6 8.3 8.9

10.1

10.5

44.9

45.1

45.3

45.5

45.6

47.4

47.4

75%II0I

26.1

27.5

28.4

30.3

33.1

35.6

40.2

41.8

33.7

33.8

34.0

34.1

34.2

47.4

47.4

50%II0I

26.1

27.5

28.4

30.3

33.1

35.6

40.2

41.8

22.5

22.6

22.7

22.8

22.8

47.4

47.4

25%II0I

26.1

27.5

28.4

30.3

33.1

35.6

40.2

41.8

11.2

11.3

11.3

11.4

11.4

47.4

47.4

75%III0

26.1

27.5

28.4

30.3

33.1

35.6

40.2

41.8

44.9

45.1

45.3

45.5

45.6

35.6

35.6

50%III0

26.1

27.5

28.4

30.3

33.1

35.6

40.2

41.8

44.9

45.1

45.3

45.5

45.6

23.7

23.7

25%III0

26.1

27.5

28.4

30.3

33.1

35.6

40.2

41.8

44.9

45.1

45.3

45.5

45.6

11.9

11.9

Net.Ir- net irrigation, Rf- Rainfall, Pe- effective rainfall, Trts-

treatments

Table B.4. Irrigation development projects constructed by World

Vision Ethiopia at Antsokia Gemza Woreda (WVE, 2009).

clxxix

Irrigati

on

scheme

Year of

construc

tion

Command

Area in

ha

No of

beneficiary

households

Scheme status

Dariga

river

2000-

2003

125 416 Functional with

little canal damage

Sal

river

right

2000-

2003

115 328 Semi functional with

intake canal damage

problem

Sal

river

left

2000-

2003


intake and

underground canal

damage problem

Gudaber

river

1995-

1996


intake canal damage

problem

Sirinka

spring

2000-

2002

80 232 Functional

Agodo

river

2001 85 425 Semi functional with

intake and half

section canal damage

problem

Chancho

river

1996-

1997

60 188 Functional with

little problem

Lay 2000- 80 216 Semi functional

clxxx

Jara

river

2002

clxxxi

Appendix C: Mean square tables for analyzed

parameters

Table C. 1. Mean square value of plant height and leaf number ofonion at Antsokia Gemza Woreda

Source of

variation

DF Plant height Leaf

number

Replication 2 17.76NS 0.20NS

Plant stage 4 67.4*** 5.0***

Irrigation 3 430.3*** 22.95***

Stage*Irrigation 12 24.2*** 1.38***

Error 38 4.70 0.38

*** Significant at P ≤ 0.001 level, DF = Degree of freedom

Table C. 2. Mean square value of fresh biomass, total bulb yield, marketable and unmarketable bulb yield of onion at Antsokia Gemza woreda

Source of

variation

DF FBM TBY Mrk Yld Unmrk

Yld

Replication 2 29.21N

S

36.9NS 36.93NS 1.02NS

Irrigation 4 976.5*

**

690.7*

**

534.48*** 7.3**

Plant stage 3 81.74*

**

114.7*

**

123.62*** 1.2NS

Stage*Irrigation 12 13.92*

*

21.55*

**

19.55*** 2.2**

Error 38 7.94 5.91 3.46 1.3clxxxii

*** Significant at P ≤ 0.001 level, ** Significant at P ≤ 0.01 level, NS = Non significant, DF = Degrees of freedom, FBM = Fresh biomass, TBY = Total biomass, Mrk= Marketable, Unmrk = Unmarketable, Yld = Yield

clxxxiii

Table C. 3. Mean square value of average bulb weight and bulb diameter of onion

Source of

variation

DF Average bulb

weight

Average bulb

diameter

Replication 2 4.22NS 0.56NS

Plant stage 4 642.69*** 0.7**

Irrigation 3 4940.41*** 10.3***

Stage*Irrigation 12 111.62** 0.48**

Error 38 36.46 0.16

* Significant at P ≤ 0.001 level ** Significant at P ≤ 0.01 level, DF = Degrees of freedom

Table C. 4. Mean square value of weight and number of big, medium and small bulb of onion

Source

of

variatio

n

DF Wt. BSB No. BSB Wt. MSB No. MSB Wt.

SSB

No. SSB

Replicat

ion

2 4.2NS 2477.4*

*

3.32NS 3821.4*

*

2.3NS 3529.3*

Plant

stage

3 40.46*** 1900.6*

**

15.17*** 1297.1*

*

0.52NS 6592.7*

**

Irrigati

on

4 223.41*

**

17123.4***

119.77*

**

12651.2***

17.52*

**

54059.5***

clxxxiv

Stage*

Irrigati

on

12 5.1NS 293.2NS 3.05* 388.3** 2.06* 1190.6*

*

Error 38 3.45 197.6 1.49 286.3 1.7 369.7

*Significant at P ≤ 0.001 level **Significant at P ≤ 0.01 level; * significant at P ≤ 0.05 level, DF = Degrees of freedom, Wt. = Weight, No. = Number, BSB = Big size bulb, MSB = Medium size bulb, SSB = Smallsize bulb

Fig. A. Evaporation measurement by using class ‘A’ pan at the

research site.

Fig. B. Bulb yield measurement by using sensitive balance.

clxxxv

Biographical Sketch

The author was born on 26 July 1982 G.C in Majettie Town of

Eastern Amhara Region. He attended his elementary and secondary

school at Majettie elementary school and at Hotie Senior

Secondary School, Dessie. After passing the Ethiopian School

Leaving Certificate Examination in 2001, he joined the former

Debub, and now Hawassa University and graduated with a B.Sc.

degree in the field of Plant Production and Dryland Farming on

July 2, 2005. He was then employed as crop production and

protection expert for two years and then vice head of

Agricultural and Rural Development office in Antsokia Gemza

Woreda of Eastern Amhara region till he joined Mekelle

University in 2009 to pursue his post graduate study in the

field of Dryland Agronomy.

E-mail- [email protected]

Tel.- +251913282228

clxxxvi

mailto:[email protected]

clxxxvii

response of bulb yield and yield components of onion (allium cepa l) for deficit irrigation in...

Documents