Water use efficiency and yield of winter wheat under different irrigation regimes in a semi-arid region

doi:10.4236/as.2011.23036

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Vol.2, No.3, 273-282 (2011)

doi:10.4236/as.2011.23036

Agricultural Scienc es

Water use efficiency and yield of winter wheat under

different irrigation regimes in a semi-arid region

Mohamed Hakim Kharrou1*, Salah Er-Raki2, Ahmed Chehbouni3, Benoit Duchemin4,

Vincent Simonneaux4, Michel LePage4, Lahcen Ouzine1, Lionel Jarlan4,5

1ORMVAH, Office Régional de Mise en Valeur Agricole du Haouz, Marrakech, Morocco; *Corresponding Author:

hakimkharrou1@yahoo.fr

2LP2M2E, Department of Physics, Faculty of Sciences and Technology, Marrakech, Morocco;

3FSSM, Faculté des Sciences Semlalia Marrakech, Morocco;

4CESBIO, Centre des Etudes Spatiales de la BIOsphère, Toulouse, France;

5Direction de la Météorologie Nationale, Casablanca, Maroc.

Received 27 May 2011; revised 19 July 2011; accepted 31 July 2011.

ABSTRACT

In irrigation schemes under rotational water

supply in semi-arid region, the water allocation

and irrigation scheduling are often based on a

fixed-area proportionate water depth with every

irrigation cycle irrespective of crops and their

growth st ages, for an equitable water supply. An

experiment was conducted during the 2004-

2005 seas on in Haouz irrigated area in Morocc o,

which objective w as 1) to evaluate the effects of

the surface irrigation scheduling method (ex-

isting rule) adopted by the irrigation agency on

winter wheat production compared to a full ir-

rigation method and 2) to evaluate drip irrigation

versus surface irrigation impacts on water sav-

ing and yield of w inter wheat. The methodology

was based on the FAO-56 dual approach for the

surface irrigation scheduling. Ground measure-

ments of the Normalized Difference Vegetation

Index (NDVI) were used to derive the basal crop

coefficient and the vegetation fraction cover.

The simple FAO-56 approach was used for drip

irrigation scheduling. For surface irrigation, the

existing rule approach resulted in yield and

WUE reductions of 22% and 15%, respectively,

compared with the optimized irrigation sched-

uling proposed by the FAO-56 for full irrigation

treatment. This revealed the negative effects of

the irrigation schedules adopted in irrigation

schemes under rot ationa l water supply on crops

productivity. It was also demonstrated that drip

irrigation applied to wheat was more efficient

with 20% of water saving in comparison with

surface irrigation (full irrigation treatment). Drip

irrigation gives also higher wheat yield com-

pared to surface irrigation (+28% and +52% for

full irrigation and existing rule treatments re-

spectively). The same improvement was ob-

served for water use efficiency (+24% and +59%

respectively).

Keywords: Water Use Efficency; Yield; Surface

and Drip Irrigation; FAO-56; Irrigation Sche duling;

Wheat

1. INTRODUCTION

Water demand has significantly increased over the last

decades while available water resources are becoming

increasingly scarce. This is mainly due to the combined

effect of climate change, persistent drought and the in-

crease of water demands related to increase in irrigated

surfaces, urbanization and tourism recreational projects.

In this context, improvement of water management in

agriculture, which is the biggest water consumer, is nec-

essary to enhance agricultural productivity in order to

meet food demands of the growing population.

The Moroccan agriculture sector contributes 19% of

the GNP and plays a substantial role in the macroeco-

nomic balance of the country. Cereal crops, mainly win-

ter wheat, occupy 75% of agricultural areas, and directly

contribute to the food security of the country [1]. How-

ever, the cereal productivity is still below the potential

mainly because of the traditional management of farms

and the climatic conditions characterized by poor and

irregular rainfall (a reduction in spring precipitation has

already been highlighted by [2]) which requires exten-

sive irrigation for cereal production stability. Therefore

in irrigated areas, a reasonable irrigation scheduling is a

M. H. Kharrou et al. / Agricultural Science 2 (2011) 273-282

274

key factor to help farmers increase crop yield and save

water regarding limited water resources. The water use

efficiency (WUE) is one of the most important indices

for determining optimal water management practices; its

use has been reviewed by [3,4]. When irrigation is ap-

plied at the critical stages of plant development, values

of WUE are larger, especially under deficit irrigation [5].

Also, high irrigation water use efficiency (WUE) for

wheat could be achieved by saving irrigation rates under

drip system [6]. This result is of great importance since

the Moroccan government has promoted the use of water

saving technologies by providing financial support for

infrastructure which requires great training and exten-

sion efforts [1].

Moreover, in irrigation schemes under rotational water

supply in semiarid environment, the existing rules for

water allocation are often based on applying a fixed-area

proportionate depth of water with every irrigation cycle

irrespective of the crops and their growth stages and that

for ease of irrigation schemes operation. This frequently

is likely to result in excessive water depths being applied

when large amount of water are available or, by contrast,

water stress periods occurring when irrigation intervals

are too large. This is the case in the area of study, the

Haouz plain, one of the most important agricultural areas

in Morocco. Thus, the effects of these irrigation sched-

uling rules on crops productivity have to be assessed in

order to improve water management.

A fundamental requirement for accurate irrigation

scheduling is to determine crop water needs or crop

evapotranspiration (ETc). The most common and practi-

cal approach used for estimating crop evapotranspira-

tion is the FAO-56 method published by the Food and

Agricultural Organization (FAO) of the UN as FAO irri-

gation and Drainage paper No. 56 [7]. This approach has

been widely used due to its simplicity and its applicabil-

ity at operational basis with satisfying results under

various climates and over several crops [8-18]. In addi-

tion to the single crop coefficient (Kc) approach, FAO-

56 introduced dual crop coefficient procedure where the

single Kc is separated into a basal crop coefficient, or

Kcb (primary crop transpiration), and a soil evaporation

coefficient (Ke). The FAO-56 dual procedure provides

an excellent framework for calculating daily ETc. How-

ever, successful application is highly dependent on the

ability to derive an appropriate Kcb curve that matches

the actual crop growth and ETc conditions that occur

during a given season [7].

Multispectral vegetation indices, such as the Normal-

ized Difference Vegetation Index (NDVI), have gained

wide acceptance for estimating several crop growth pa-

rameters. Several studies have highlighted the potential

of using NDVI for crop coefficients estimation [10,12,15,

17]. In this study, we have used ground radiometric mea-

surements to derive NDVI-based Kcb and NDVI-based

fraction cover (fc) along with the FAO-56 dual proce-

dure to schedule surface irrigation and the single Kc pro-

cedure for drip irrigation scheduling.

It has been found that the impact of limited irrigation

and soil water deficit on crop yield or WUE depends on

the particular growth stage of the crop, and the most

sensitive stage can vary region-by-region due to regional

variability in environment and agronomic practices [19].

In the Mediterranean region, [20] reported that wheat

response to water stress is more sensitive from stem-

elongation to booting, followed by anthesis and grain-

filling stages. For the Loess Plateau of China, [21] found

that winter wheat sensitivity to drought occurs, in de-

creasing order of importance, during the stages of anthe-

sis, booting, stem elongation, and grain filling.

Although relationships between wheat Grain yield

(GY) and amounts of water applied or evapotranspira-

tion, reported by several authors, have been widely used

as a guideline for irrigation [4,20,22], the effects of tim-

ing applications, dictated by the irrigation schedules, on

wheat GY and WUE cannot be explained by these rela-

tionships. So, the objective of this research was to evalu-

ate the effects of the existing rules of surface irrigation

allocation and scheduling in a rotational irrigation sys-

tem on yield and water use efficiency of winter wheat in

a semi arid environment. Also, a comparison with drip

irrigation method was included in the study.

2. MATERIALS AND METHODS

2.1. Experimental Site and Data Collection

Field experiment was conducted during 2004-2005

season at the experimental station of the irrigation

agency called Office Régional de Mise en Valeur Agri-

cole du Haouz (ORMVAH). This station which is about

6 hectares was created in 1990 and located 15 km West

of Marrakech city in an irrigation scheme (latitude

31˚37′56″N, longitude 8˚09′24″, 412 m over mean sea

level). The climate of the region is typically Mediterra-

nean semi-arid, with around 250 mm of average annual

rainfall, concentrated mainly from autumn to spring, and

an average annual reference evapotranspiration (ETo) of

about 1600 mm. The soil at the experimental site is a

silty clay loam with a bulk density of 1.4 g/cm3. Winter

wheat (“Arrehane 1774” cultivar) was sown on 8th De-

cember 2004 at a rate of 216 Kg/ha. The experimental

area consisted of two plots PG3 and PL3 of 0.60 and

0.36 ha respectively.

All the experimental plots had the same characteristics

and the same crop management practice (soil preparation,

fertilizer and pest control etc.) and they were fallowed

M. H. Kharrou et al. / Agricultural Science 2 (2011) 273-282

275275

since 2002. They differ only in the irrigation timing and

water amounts applied in order to limit the complexities

in the discussion of the influence of different irrigation

scheduling rules. Fertilizer was applied manually in four

split applications, with the first application at planting,

consisting of 200 kg·ha−1 of ammonium sulfate (21% N),

225 kg·ha−1 of triple super phosphate (45% P2O5), and

100 kg·ha−1 of sulfate of potash (48% K2O). The other

applications were at 51, 100 and 121 days after planting

and included 133, 109 and 72 kg·ha−1 of urea respec-

tively. Weeds were controlled with specific chemical

applications. A weather station installed in the experi-

mental station provided hourly measurements of climatic

parameters (solar radiation, wind speed, relative humid-

ity, and air temperature). Punctual measurements of soil

water content at different depths (from 0.10 m to 0.80 m)

were made using gravimetric soil water sampling. Also,

crop height (Ht) and root depth (Zr) were measured dur-

ing the growing season.

In order to assess wheat crop phenology and evaluate

the irrigation treatments effects on it, the Leaf Area In-

dex (m²/m²) was measured every two weeks using hemi-

spherical photographs, based on a method calibrated in a

previous study using LAI ground measurements [23].

Before harvesting, five 1 m2 plots were selected at ran-

dom to measure the grain yield components and yield

was measured by weighing after harvesting.

Finally, measurements of canopy reflectance were

carried out using a hand-held radiometer (MSR87 Mul-

tiSpectral Radiometer, Cropscan Inc., USA) at the same

dates of hemispherical photo shots. From the reflectance

measurements, the normalized difference vegetation

index [24] was computed. In addition, the fraction cover

of the vegetation was derived from NDVI using a rela-

tionship previously calibrated on this crop in the area

[12]:





f1.18NDVI NDVI min

(1)

where NDVImin is the NDVI value for the bare soil equal

to 0.147.

2.2. Irrigation Treatments and Irrigation

Scheduling Methods

Two surface irrigation scheduling treatments were ap-

plied in the PG3 plot, with two replications each: irriga-

tion scheduling based on the FAO-56 dual procedure

(full irrigation) and irrigation scheduling according to

the existing rule adopted by the irrigation agency (exist-

ing rule approach). Another treatment (drip irrigation)

consisting of FAO-56 single approach for drip irrigation

scheduling was employed within PL3 plot.

The irrigation amounts applied were volumetrically

measured using records of water level in a tank with 200

m3 capacity in the surface irrigation case and, using a

water meter in the drip irrigation case.

For the two surface irrigation treatments, the border

system, which is the most common irrigation practice in

the region, was adopted and the water was applied to

strips of 5 m wide and 25 m length. The drip irrigation

system adopted comprises a laterals spacing of 1.0 m

which were 16 mm in diameter. The emitters were inline

type with spacing of 0.4 m and had 4.0 l/h flow rate at

1.0 atm pressure.

The irrigation is scheduled, in the case of existing rule

approach, according to the water delivery schedules pre-

pared by irrigation managers for the irrigation scheme.

Predetermined annual quota according to surface water

availability in dams is allocated for irrigation at the be-

ginning of the season. This water volume is distributed

on a fixed-area proportionate water allocation basis pro-

viding the same water depth per hectare to farmers. Then,

the dates and duration of water delivery to the fields

(using rotational irrigation) are pre-sets for every irriga-

tion cycle throughout the season in arrangement with the

Water User Associations representing the farmers of the

irrigation scheme.

In the case of full irrigation treatment, the timing and

the amounts of water to apply were planned in order to

avoid crop water stress. Thus, irrigation was scheduled

to cancel the soil water depletion and the water depth

was calculated in order to bring the soil water content to

its total available water (TAW). The irrigation timing, in

this case, is determined when the stress coefficient (Ks)

reached a threshold value considered equal to 0.6 for the

wheat according to [25].

The irrigation is scheduled, for drip irrigation treat-

ment, based on the soil water balance method in which

the drainage and runoff were neglected and the net irri-

gation depth was estimated by subtracting the rainfall

from the calculated crop evapotranspiration on daily

basis using this relationship:

IRETo KcR



 (2)

where IR, ETo, Kc and R refer respectively to net depth

of irrigation (mm·d−1), reference evapotranspiration

(mm·d−1), crop coefficient and rainfall (mm·d−1).

2.3. FAO-56 Procedure Parameters and

Water Use Efficiency

The FAO-56 is based on the concepts of reference

evapotranspiration ETo and crop coefficients introduced

to separate the standard climatic demand (ETo) from the

plant response ETc [7]. The single method relies on the

following equation:

ETcKc ETo



 (3)

M. H. Kharrou et al. / Agricultural Science 2 (2011) 273-282

276

where Kc is the single crop coefficient. The daily refer-

ence evapotranspiration, ETo, is calculated according to

the FAO Penman-Monteith method [7]. Daily values of

the climatic parameters used for calculating ETo are ob-

tained from the weather station installed in the experi-

mental station.

The dual method accounts for variations in soil water

availability, inducing either stress and soil evaporation,

and is based on the following equation:



cb e

ETcKs KKETo (4)

where Kcb is the basal crop coefficient derived from

NDVI using this previously calibrated relationship for

wheat crop in the region [23] :





cb min

K1.64NDVI NDVI  (5)

Ke and Ks are calculated based on daily water balance

computation in the surface soil evaporation layer of ef-

fective depth (Ze) and in the root zone (Zr), respectively,

according to [7].

The soil parameters that were used in the FAO-56

procedure for calculating Ke, Ks and thus crop evapo-

transpiration (ETc) are presented in Table 1.

p is the fraction of TAW that a crop can extract from

the root zone without suffering water stress. The rec-

ommended values for p, given in Table 2 of FAO-56

paper [7], apply for ETc ≈ 5 mm/day. In this study, the

value for p was adjusted for different ETc according to p

= p (the table 22 in FAO-56 paper) + 0.04x(5 – ETc) [7].

The FAO-56 dual procedure for the full irrigation

treatment was implemented using a software developed

in EXCEL [7]. Once the model parameters were updated

using data collected, and in order to predict future dates

and amounts of irrigation, daily average climatic data

(ETo, wind speed and relative humidity), and linear ex-

trapolations for crop parameters (Kcb, fc, crop height Ht

and root depth Zr) were used. Since, the water balance

approach for irrigation scheduling is based on estimates

and is not always accurate, actual readings of crop height

(Ht) and root depth (Zr) were taken during the growing

season to adjust the predictions, and also the measured

Tab le 1 . The soil parameters used for the determination of Ke,

Ks and crop evapotranspiration (ETc) following the FAO-56

methodology.

Soil parameters Values

Field capacity, θFC (m3/m3)

Wilting point, θwp (m3/m3)

Maximum effective rooting depth, Zr (m)

Depth of the evaporation soil layer, Ze (m)

Total evaporable water, TEW (mm)

Readily evaporable water, REW (mm)

Total available water, TAW (mm/m)

Wetting fraction, fw (fraction)

Readily available water, RAW (mm/m)

0.36

0.20

0.80

0.12

165

1.0

p × TAW

soil water was used to update, if necessary, the estimated

Root zone depletion (Dr) [26].

In the case of existing rule treatment, although irriga-

tion was not driven by FAO budget, the same parameters

as for full irrigation plots were observed and computed

in order to compare the two treatments and especially

their effects on stress.

Finally, for drip irrigation treatment, the crop evapo-

transpiration was calculated using the FAO simple crop

coefficient approach with Kc values of 0.30 for Kcini,

1.15 for Kcmid and 0.4 for Kcend taken directly from the

table 12 in FAO-56 paper [7].

Water use efficiency (WUE, kg·m−3) regarding yield

was finally calculated as [27]:

WUE0.1GY / ET



 (6)

where ET (mm) is the evapotranspiration calculated

using the previous FAO method and GY is the measured

Grain Yield (kg·ha−1).

3. RESULTS AND DIS CUSSION

3.1. Water Consumption

The irrigation timing and the water depths applied for

the different irrigation schedules are shown in Table 2.

The main difference between three treatments was the

annual amount of irrigation water, which was 455, 396

and 362 mm for full irrigation, existing rule and Drip

irrigation treatments, respectively. Because the season

was dry (only 52 mm amount of rainfall during the

growing cycle), the irrigation water was very important

and represented about 90% of the total water applied.

Drip irrigation scheduling was found to be more efficient

with water saving of about 20% comparatively to surface

irrigation with the full irrigation approach. The latter

consumes 10% more water than the existing rule ap-

proach to avoid crop stress. Also, it can be seen that for

Table 2. Irrigation date and water amount (mm).

water amount applied per treatment (mm)

Irrigation date Full

irrigation

Existing

rule

Drip

irrigation

12/22/0476.5

DEC 12/23/04 70

01/13/05 68

JAN 01/14/0565.5 65

02/02/0557

FEB 02/16/05 64.5

03/17/05115

MARCH 03/20/05 57.5

111

04/02/05 136

APRIL 04/04/05141 95

TOTAL Irrigation 455 396 362

TOTAL Rainfall 52 52 52

TOTAL

(Irrigation + Rainfall) 507 448 414

M. H. Kharrou et al. / Agricultural Science 2 (2011) 273-282

277277

surface irrigation treatments, the number of irrigation

events was same for both treatments (5 irrigations ap-

plied). The existing rule and full irrigation schedules

proposed very close amounts and irrigation dates at the

beginning of the growing period (December-January)

but results strongly differ during the core of the season.

Indeed, a strong delay of the irrigation event in February

was observed for the existing rule treatment compara-

tively to full irrigation and the water depth applied was

significantly lower in March. The consequences of these

discrepancies on the wheat development are analyzed

hereafter.

3.2. Crop Phenological Response to

Irrigation Method

Figure 1 displays the seasonal time courses of LAI

(Figure 1(a)) and NDVI (Figure 1(b)) for the three irri-

gation methods described above. The two variables show

comparable seasonal patterns following the dynamics of

(a)

(b)

Figure 1. Seasonal time course of LAI and NDVI of winter

wheat for the three irrigation treatments.

crop growth. It can be seen that irrigation scheduling had

a significant influence on LAI (Figure 1(a)); the ob-

served LAI was higher for drip irrigation treatment, with

maximum values being 4.8, 5.1 and 5.8 m2/m2 respec-

tively for the existing rule approach, full irrigation and

drip irrigation treatments. These globally high values of

LAI (>4) indicate acceptable growth conditions for all

treatments. However, it can be seen that the delay of 14

days in the date of irrigation on February (57th day after

sowing) for the existing rule treatment has produced a

crop growth slow-down and a LAI reduction suggesting

that the crop has experienced a water stress. It can be

inferred that with adequate water application, LAI can

be increased so that light energy is better utilized and the

crop development is improved.

The NDVI minimum value was measured at the be-

ginning of the growing cycle over the dry bare soil and

was about 0.147 in agreement with the value obtained

previously in the same region [23]. As the Leaf Area

Index, the NDVI increased from crop emergence until

maximum value was attained about 93 days after sowing

(Figure 1(b)) and then began to decrease rather sharply

through the end of the season. NDVI maximum values

were 0.88, 0.91 and 0.95 for existing rule approach, full

irrigation and drip irrigation treatments respectively. The

NDVI curves remains flat out at mid-season as the

NDVI saturates for high values of LAI as previously

reported by [23]. The NDVI values were slightly higher

for drip irrigation treatment than the two surface irriga-

tion treatments especially during the late-season since

the crop was still irrigated by drip system which delayed

the crop senescence. Also, NDVI values were slightly

higher for the full irrigation treatment than existing rule

treatment especially during the mid and late-season

which indicated that the crop has experienced a water

stress induced by a long irrigation interval in February

which coincides with stem extension stage and the insuf-

ficient water amount applied for the forth irrigation

event which coincided with the flowering stage.

3.3. Performance of FAO Dual Procedure for

Irrigation Scheduling

3.3.1. Crop Coefficients

The Kcb average values obtained at three stages (ini-

tial, mid-season and end-season) were 0.14, 1.20 and

0.29 respectively, with a maximum of 1.27 for full irri-

gation treatment, and 0.18, 1.16 and 0.25 respectively

with a maximum of 1.21 for existing rule treatment.

These values are slightly different than those given by

[7] (Kcbini = 0.15, Kcbmid = 1.10, Kcbend = 0.25) since

the Kcb derived from NDVI measurements reflects the

local conditions.

M. H. Kharrou et al. / Agricultural Science 2 (2011) 273-282

278

This result illustrates the interest of remote sensing

data to derive Kcb values since it offers first the ability

to account for variations in plant growth due to specific

weather conditions, and also improved irrigation sched-

uling due to better estimation of water use and more ap-

propriate timing of irrigations [10,28].

During the initial stage, there were no differences be-

tween the adjusted Kc (Kc-adj = Kcb·Ks + Ke) and Ke

values for the two treatments since the irrigation events

occurred at almost the same time suggesting a similar

crop development. However, the existing rule scheduling

approach adopted by the irrigation managers implies a

large irrigation interval (34 days between the second and

the third irrigation, and 14 days between the two treat-

ments for the third irrigation) which caused a decrease of

the Kc-adj and Ke values. In particular, the Kc-adj

reached a minimum value of 0.33 indicating a strong

water stress effect.

The stress coefficients Ks calculated for the two sur-

face irrigation treatments were also compared (Figure 3).

In the case of existing rule treatment, as explained pre-

viously, winter wheat experienced a water stress at the

crop-development stage due to the large irrigation inter-

(a)

(b)

Figure 2. Evolution of crop coefficients during the winter

wheat crop season under two surface irrigation treatments: (a)

full irrigation, (b) existing rule.

Figure 3. Estimated daily stress coefficient Ks by the FAO-56

dual Kc approach for full irrigation and existing rule treatments

during 2004-2005 growing season. Amounts and dates of irri-

gation applied for both treatments are also shown.

val, the Ks decreased below the threshold value for 10

days. Also, due to the insufficient water quantity applied

during the fourth irrigation event, the Ks started to de-

cline earlier than for the full irrigation treatment.

This experiment revealed that although the irrigation

scheduling adopted by the irrigation agency proposed

the same number of irrigation events as those required

by the FAO method used for the full irrigation schedul-

ing (five irrigations received throughout the season), the

irrigation timing and water amounts were not optimal

suggesting an inadequate water irrigation delivery. In

fact, in Haouz irrigated schemes, as previously explained,

the irrigation depths are defined for each irrigation cycle,

in an equitable manner (a fixed-area proportionate water

amount for all farmers) according to the water availabil-

ity in reservoirs irrespective of the crops and their

growth stages.

3.3.2. Soil Water Depletion

The crop water stress is also appreciated by analyzing

the root zone soil water depletion (Dr) during the crop

season. Figure 4 illustrates Dr estimated by the FAO

procedure for the two treatments: full irrigation treat-

ment (Figure 4(a)) and existing rule treatment (Figure

4(b)).

The total available water (TAW) curve increases dur-

ing the crop season regarding the root development

which reached a maximum value of 0.80 m according to

the root depth measurements made during the season.

The readily available water (RAW) curve shows some

variations during crop season due to the ratio of RAW to

TAW parameter “p” which varies with the daily crop

evapotranspiration.

Since the 2004-2005 season was dry (with a precipita-

tion of 116 mm from September 2004 to August 2005

which is lower than the regional climatic average of 240

M. H. Kharrou et al. / Agricultural Science 2 (2011) 273-282

279279

(a)

(b)

Figure 4. Daily estimated root zone depletion (Dr), Total

available water (TAW) and readily available water (RAW) for

two treatments: (a) full irrigation and (b) existing rule. Rainfall

and irrigation are also plotted in the same figure.

mm), it can be noticed that the rainfall throughout the

growing cycle has slightly contributed to the soil water

moisture and the irrigation has played an important role

in the soil water depletion reduction (Figure 4). How-

ever, the two peaks of precipitation (14 and 22 mm re-

spectively) that occurred on 59th and 63th day after sow-

ing (DAS) have reduced the soil water depletion without

cancelling it. Thus, Dr was maintained close to RAW in

the case of full irrigation treatment during this period

and it was lower for existing rule treatment suggesting

acceptable soil moisture level since the third irrigation

water was still stored in the soil contributing to the crop

evapotranspiration.

In addition, for existing rule treatment, the water de-

pletion Dr exceeded the RAW for a long period (be-

tween the 57th and the 71th DAS) and also the fourth ir-

rigation depth applied on 102th DAS was not sufficient

to meet the actual Dr and offset the depletion resulting in

a deficit irrigation condition. This has affected the crop

development and productivity (see section 3.4). Finally,

the soil root zone water depletion seems to be fairly well

simulated by the model since it was updated only two

times throughout the season (33th and 85th DAS) for the

two treatments.

3.4. Grain Yield and Water Use Efficiency

The grain yields and Water Use Efficiency obtained

for the different irrigation schedules are shown in Table

3. Regarding the grain yield, it was 50, 39 and 62 quin-

tals/ha for the three treatments (full irrigation, existing

rule and Drip irrigation) respectively. It was observed

that the grain yield obtained with drip irrigation was

24% higher than full irrigation treatment and 59% higher

than the existing rule treatment. In addition, with exist-

ing rule treatment, there was a significant reduction in

the crop yield. Indeed, the yield reduction obtained was

about 22% in comparison with the full irrigation treat-

ment, which shows the negative effects of the rules

adopted by the managers for irrigation scheduling at

scheme level on the crops productivity.

The low yield obtained with existing rule treatment

could be explained, as previously highlighted, by the

crop water stress since all crop management factors were

similar for all treatments. Indeed, the water stress was

caused by the large irrigation interval on February which

occurred during the stem extension stage and reduces the

number of heads/m2 (up to about –11%) in accordance

with previous findings [29,30], and by the insufficient

water amount applied in March which occurred during

the heading and flowering stage and coincided with high

ETo values, affecting the grain formation especially the

number of seeds/head. This result was consistent with

the findings of [20], who reported that the most sensitive

stage of winter wheat to water stress was from stem

elongation to booting, followed by anthesis and grain-

filling.

The WUE was 0.99, 1.17 and 1.50 Kg/m3 for the three

treatments (full irrigation, existing rule and drip irriga-

tion) respectively. With surface irrigation, the WUE was

improved by 18% when irrigation is scheduled optimally

according to FAO method as compared with existing

rule treatment. Drip irrigation showed better result since

the WUE was improved by 52% and 28% when com-

pared with surface irrigation respectively the existing

rule and full irrigation treatments.

These results revealed that high water use efficiency

Table 3. Grain yield and WUE for the three irrigation treat-

ments.

Full irrigation Existing rule Drip irrigation

Grain yield

(quintals/ha) 50 39 62

WUE (kg/m3) 1.17 0.99 1.50

M. H. Kharrou et al. / Agricultural Science 2 (2011) 273-282

280

could be achieved either by improving yield and saving

water under drip irrigation system. Also, even with sur-

face irrigation method, good management of irrigation

water (i.e. better irrigation scheduling) could lead to a

better water use efficiency. The values obtained are close

to those found in other studies [4,20,31-34]. It was re-

ported that in general, the wheat WUE ranges from 0.40

to 1.83 kg/m3 globally on a yield basis. For example,

with the irrigated wheat in the US southern plains, WUE

was 0.50 - 1.20 kg/m3 with a yield of 3000 - 8000 kg/ha

[4,31,32]. A higher WUE of 0.70 - 1.51 kg/m3 in winter

wheat was found in the North China Plain [20,33,35].

Recently, [32] reported a much higher WUE of 0.97 -

1.83 kg/m3 in winter wheat in the North China Plain

(NCP). With drip irrigation, WUE values of 1.13 - 1.20

kg/m3 for wheat were found in North Sinai (Egypt) de-

pending on the drip system adopted [6]. A high effi-

ciency of water use is extremely important for farmers

and irrigation agencies in water scarce areas.

4. CONCLUSIONS

Irrigation schemes in semi-arid environment are gen-

erally subject to rotational irrigation supply based on

fixed-area proportionate water depths applied every irri-

gation cycle irrespective to crops and their growth stages.

In this study, a dedicated experiment was conceived and

implemented to evaluate the effects of the existing rule

of surface irrigation allocation and scheduling in such

rotational irrigation systems on yield and water use effi-

ciency of winter wheat compared to a full irrigation ap-

proach and the drip irrigation method, both based on

FAO-56 procedure. The results showed that irrigation

scheduling methods had obviously significant effects on

growth and yield of winter wheat.

For surface irrigation, the existing rule approach re-

sulted in yield and WUE reductions of 22% and 15%,

respectively, compared with optimized irrigation sched-

uling proposed by the FAO-56 for full irrigation treat-

ment. This revealed the negative effects of the irrigation

schedules adopted in irrigation schemes under rotational

water supply on crops productivity. Considering the ab-

solute necessity for water saving and sustainable food

production, it can be recommended to irrigation manag-

ers to move from equitable, and rigid delivery schedules

to more flexible delivery system operation and crop-

based schedules.

The results also suggested that incorporating remote

sensing-based vegetation indices, such as NDVI, used to

derive Kcb for the FAO method provides an opportunity

to improve irrigation scheduling by a better estimation of

water use and a more appropriate timing of irrigations.

This study has demonstrated also that drip irrigation

could be applied to the wheat crop, usually cultivated in

rotation with other crops, which may justify the drip

irrigation system adoption by farmers but economic pa-

rameters are to be considered more closely.

It is also demonstrated, as expected, that drip irriga-

tion applied to wheat was more efficient with 20% of

water saving in comparison with surface irrigation (full

irrigation treatment). Drip irrigation gives also higher

wheat yield compared with surface irrigation (+28% and

+52% for full irrigation and existing rule treatments re-

spectively). The same improvement was observed for

water use efficiency (+24% and +59% respectively). It

can be recommended that, flexibility of on-farm irriga-

tion scheduling can be improved by providing a storage

capacity (reservoirs) below the delivery point, so as to

compensate for the expected mismatch, especially in

time, between deliveries and consumption. Water can be

pumped from the reservoir, which implies additional

investment and operating costs but may allow the appli-

cation of drip irrigation and also the conjunctive use of

groundwater with the surface water when this latter is

not available.

5. ACKNOWLEDGEMENTS

This study was supported by SUDMED (IRD-UCAM) funded by

the European Union (PCRD). The authors thanks the SudMed techni-

cal partners especially ORMVAH (‘Office Regional de Mise en Valeur

Agricole du Haouz’, Marrakech, Morocco) for its technical help and

for access to use the field site.

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