IMPROVING WATER USE EFFICIENCY OF FIELD CROPS THROUGH REGULATED DEFICIT IRRIGATION

Fadi KaramLebanese Agricultural Research InstituteDepartment of Irrigation and Agro-Meteorology - Tal Amara (http://www.lari.gov.lb)

Kamal KaraaLitani River AuthorityDepartment of Rural Development – Beirut – Lebanon

Nazir TarabeyAssociation of Irrigation Water Users in South Bekaa Scheme – Lala - Lebanon

WASAMED – International Conference on “Water Saving in Mediterranean Agriculture & Future Research Needs”, IAMB, Bari, 14-17 February 2007

Efficiency

Is the ratio OUTPUT INPUT

Irrigation efficiency (Ei)

Agronomic water use efficiency (WUEa)

Physiological water use efficiency (WUEp)

YIELD OR BIOMASS (kg m-2) WUEg,b (kg m-3) =

EVAPOTRANSPIRATION (m(m3 mm--2))

(1 kg m-3 = 1 g m-2 mm-1)

Subscripts g and b indicate grain yield and biomass

Agronomic water use efficiency (WUE)

Water saving approach

Develop new irrigation scheduling, not necessarily based on full crop water requirement, but one designed to ensure the optimal use of allocated water: Partial irrigation

Deficit Irrigation

DI or RDI is one way of maximizing water use efficiency (WUE) for higher yields per unit of irrigation water applied.

The crop is exposed to a certain level of water stress either during a particular growth period or throughout the whole growing season, without significant reduction in yields.

Objectives

Increase WUE of a crop by eliminating irrigations that have little impact on yield.

Yield reduction may be small compared with the benefits gained through diverting the saved water to irrigate other crops.

YIELD RESPONSE TO WATER

Yields increase with water availability in the root zone, until a saturation level, above which there is little effect.

Yield response curve of specific crops depends on weather conditions and soil type as well as agricultural inputs.

EXPERIMENTAL PLAN

Maize, a determinate species with a limited capacity to adjust grain yield in response to water availability (Karam et al, 2000; 2003);

Soybean, an indeterminate species with a high capacity to compensate the effects of early water stresses (Karam et al., 2005);

Cotton, an indeterminate species with a larger capacity to adjust the number of dehiscent bolls under stressful conditions (Karam et al., 2006);

Sunflower, a determinate species with a single inflorescence and an aptitude to tolerate moderate water stresses (Karam et al., 2007).

Irrigation treatments

Crop Period Treatment Period of irrigation cutout I-100 No irrigation restriction Corn 1998-

1999 I-80 I-60

80% of soil replenishment 80% of soil replenishment

C No irrigation restriction S-1 Irrigation cutout at full bloom (R2) S-2 Irrigation cutout at seed enlargement (R5)

Soybean 2000-2001

S-3 Irrigation cutout at mature seeds (R7) C No irrigation restriction S-1 Irrigation cutout at first open boll S-2 Irrigation cutout at early boll loading

Cotton 2001-2002

S-3 Irrigation cutout at mid boll loading C No irrigation restriction S-1 Irrigation cutout prior to flowering stage S-2 Irrigation cutout at mid flowering stage S-3 Irrigation cutout at the beginning of seed

formation

Sunflower 2003-2004

S-4 Irrigation cutout at mid seed ripening

SOIL-WATER BALANCE

Dynamic-oriented Process

Where t2–t1 is the time interval over which measurements are made, zo is the soil surface and z is the depth to the lowest point of measurement and is the volumetric soil water content.

2

1

2

10

0

t

t

t

t

z

z

t tdtDrR

ACTUAL SOIL MOISTURE CONTENT

t is actual moisture content of the root zone at time step t (cm3 cm-3)INup is rate of net influx through the upper root zone boundary (cm d-1)

INup = P + Ie – Es + SSt/ t - SR

INlow is rate of net influx through the lower root zone boundary (cm d-1)

INlow = CR - Perc

Ta is actual transpiration rate of crop (cm d-1)RD is actual rooting depth (cm); P is precipitation intensity (cm d-1)Ie is effective daily irrigation (cm d-1); Es is soil evaporation rate (cm d-1)SSt is surface storage (cm); SR is rate of surface runoff (cm d-1)CR is rate of capillary rise (cm d-1); Perc is percolation rate (cm d-1)t is time step (cm d-1); Zt is depth of groundwater table (cm).

talowup

t RD

TININ

)(

SOIL WATER CONTENT

2

1

z

zzAT

A = Root Absorption

Z = soil depth

Soil Water Balance

0

10

20

30

40

50

60

70

Days after sowing

Rai

n, E

Tp

(mm

)

-200

-100

0

100

200

300

400

500

Soil

wat

er c

onte

nt (

mm

)

Rain (mm) ETP (mm) SW (I-0) SW (I-50) SW (I-100)

I-100 (50 mm)

I-100 (50 mm)

I-0 (7.5 mm)

I-50 (50 mm)I-50 (7.5 mm)I-100 (7.5 mm)

(FC)

(PWP)

SOIL WATER MONITORING AND MEASUREMENTS

CAPACITANCE PROBE

DISADVANTAGES

The system requires highly qualified technicians for installation and maintenance and highly qualified personnel for running the system i.e. farmer by himself cannot use the system.

Very expensive system System fragile and subject to vandalism. Can be affected by climate adversity (flooding, heavy

rain, etc) Radio transmission can be affected by nature barrier or

geographical relief Problems of data discontinuity or delaying due to radio

or other tele-communication interference

Soil moisture measurement

Method of measurement: TDR (Time Domain Reflectometry)

Frequency: before and after irrigation supplies, at 30 cm increment in the 0-120 cm of soil depths.

Weighing Lysimeter (ETcrop)

ET measurements (Hourly and Daily)

Location (middle of the Exp. field)

Area (4 4 m²)Depth (1 m)Weight (22000 kg)Watered at 30% of SWDLinked to a weight

indicatorWeight loss recorded (4

times/hr; 94 readings/day)

Rye-grass drainage Lysimeters (ETrye-

grass)

ET measurements (3-to-4 day interval)

Location (middle of the Exp. field)

Area (2 2 m²)Depth (1 m) Watered at 30% of SWDET = I – D ± Q(Q = 0 when irrigation is

frequent)

METHODOLOGY

First year ETref (Rye-grass

drainage lysimeters) ETcrop (weighing or

drainage lysimeters) Kc = ETcrop/ETref

Second year ETref (Rye-grass

drainage lysimeters) ETcrop = ETref x Kc

Climatic-Water Balance: FAO Penman-Montheith

234.01273

900408.0

UT

eeGR

ET

dan

o

ETcrop = ETo × Kc

0

0.2

0.4

0.6

0.8

1

1.2

Days after sowing

Kc

Vegetative phase

Reproductive phase

Grain filling phase

Sowing Harvest

ETo FAO-PM vs. ETrye-grass

2001 grwing period

y = 0.8321x + 1.5567

R2 = 0.785

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

ETrye-grass (mm/day)

ET

p F

AO

-PM

(m

m/d

ay

)1:1

Daily and Seasonal Evapotranspiration

0

2

4

6

8

10

12

0 9 18

27

36

45

54

63

72

81

90

99

10

8

11

7

12

6

13

5

14

4

d.a.s

mm

pe

r d

ay

0

100

200

300

400

500

600

700

800

mm

ETm ETcum

Daily ETm, ETo and Kc

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 9 18

27

36

45

54

63

72

81

90

99

10

8

11

7

12

6

13

5

14

4

d.a.s

mm

pe

r d

ay

0.00.10.20.30.40.50.60.70.80.91.0

Kc

Kc-grass ETo-grass ETm

Kc-FAO vs. kc-grass

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Kc grass

Kc

FA

O

Line 1:1Y = 0.65 X + 0.1 ( r² = 0.67; n = 147)

Soybean (2000-2001)

(Karam et al., 2005; data points are means of five quadrates of 1m2 each per treatment)

y = 1.5797x + 2005.3

R2 = 0.0494

0

500

1000

1500

2000

2500

3000

3500

4000

0 100 200 300 400 500 600 700 800 900

ET (mm)

Seed

Yie

ld (

t/ha

)

y = 6.1554x + 3087.7

R2 = 0.3924

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 100 200 300 400 500 600 700 800 900

ET (mm)

Bio

mas

s (t

/ha)

Results are a kind of database for the country

Corn seasonal ET reached on the lysimeter 952 mm in 1998 and 920 mm in 1999. Grain-related water use efficiency (WUEg) varied in corn treatments from 1.34 to 1.88 kg m-3, while at biomass-basis (WUEb) the values varied from 2.34 to 3.23 kg m-3.

Soybean seasonal ET totaled 800 mm in 2000 and 725 mm in 2001. Seed-related water use efficiency of soybean (WUEs) varied from 0.47 to 0.54 kg m-3, while WUEb varied from 1.06 to 1.16 kg m-3.

Cotton, seasonal ET was 641.5 mm in 2001 and 669.0 mm in 2002. Average WUEl values varied among treatments from 0.43 to 0.64 kg m-3, while WUEb varied from 1.82 to 2.16 kg m-3.

Sunflower, average across years of evapotranspiration attained 672 mm. WUEs of sunflower varied among treatments from 0.76 to 0.87 kg m-3, while at biomass-basis WUEb varied from 3.46 to 4.1 kg m-3.

Concluding remarks

Improvement of water use efficiency requires information on water consumption by the crop

Use of modern irrigation methods can result in less water losses

More experiments are needed with respect to different agro-climatic zones.