Soil Environ. 34(2): 156-165, 2015
www.se.org.pk

Online ISSN: 2075-1141
Print ISSN: 2074-9546

Assessment of actual evapotranspiration and yield of wheat under
different irrigation regimes with potassium application
Muhammad Imran1, Anwar-Ul-Hassan2, Muhammad Iqbal2, Ehsan Ullah3 and Jirka Šimunek41
Department of Soil and Environmental Sciences, Ghazi University D.G. Khan
2
Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad
3
Department of Agronomy, University of Agriculture, Faisalabad
4
University of California Riverside, USA

Abstract
Water shortage at precarious growth stages diminishes the wheat production, however regulated deficit
irrigation and potassium fertilization ameliorate its adversities to a certain extent. A pot experiment was conducted
in 2010-11 and 2011-12 growing seasons to assess the effect of regulated deficit irrigation on yield and water use
efficiency of wheat under semiarid region of Pakistan. The growing season was divided into six periods viz:germination, jointing, booting, heading, grain filling and maturity stage. Three regulated deficit irrigation levels(no- soil- water- deficit (H: 80-100 % of available water content (AWC)), medium (M) soil water deficit (70 to 80%
AWC and severe (L) water deficit (60-70% AWC) were maintained at above mentioned stages in combination withthree levels of potassium (0, 200 and 300 kg ha-1 K2O). Soil water contents were measured gravimetrically byweighing pots after 1 to 2 day’s interval throughout the growing season. Potential evapotranspiration (ETp) was
calculated using Penman-Montieth model. The actual evapotranspiration (ETa) was calculated using water balance
equation and crop coefficient was calculated by dividing the ETa with ETp. The data obtained was analyzed
statistically. The results of this study showed that grain yield and water use efficiency in wheat (Sahar-2006) was
greatly improved by 23.4 and 15.0% (average of two years) under soil water deficit treatment I 3 (MMHMH) withpotassium (K2O applied at 300 kg ha-1) as compared to regulated deficit treatment I1 (HMLML) in combination
without potassium (K2O applied at 0 kg ha-1). The optimum total irrigation water of 242.9 mm was distributed as
13.7 mm during germination stage, 22.15 mm during jointing, 21.10 mm during booting, 69.95 mm during heading,
58.9 mm during grain filling and 57.05 mm during maturity to fulfill the need of actual evapotranspiration which
was required to produce the above mentioned increase in grain yield and other parameters. Root length and massdensity were also increased by 35.9 and 35.6% in pot receiving I 3 (MMHMH) in combination with K2 over I1(HMLML) in combination with K0. K nutrition helped in mitigating the negative effects of water stress due to welldeveloped root system and accelerated the maximum water uptake and improved water use efficiency.
Keywords: Wheat, water use efficiency, regulated deficit irrigation, actual evapotranspiration, crop coefficientIntroduction
Wheat (Triticum aestivum L.) is one of the mostimportant and extensively grown cereal crops in the world.
It is grown for its grains and straw and area under its
cultivation is about 228 million hectare around the world. In
area and production it ranks first at global level and isstaple food for about one third population of the world(Anonymous, 2012-13). In Pakistan it is also consumed as astaple food (Anonymous, 2012-13). Soil moisture isconsidered as one of the most significant factors for poor
yield of wheat. Low crop water productivity of wheat (0.61.7 kg m-3) offers incredible opportunities for increasing or
at least maintaining production of agricultural crops with aless amount of water (Zwart and Bastiaanssen, 2004).

One possible way to maximize yields per drop of water
is the regulated deficit irrigation (RDI) (English and Raja,
1996). Saved water benefits are more significant than thelosses of yield reduction by deficit irrigation especially inareas where water availability is limited (Eck et al., 1987).
There is a linear relation between crop growth andirrigation levels. Water deficit at jointing (50-60% of field
capacity) and at both booting and heading (65-70% of field
capacity) followed by late reproductive period (50-60 % offield capacity) resulted in 25% increase in yield of wheat(Alderfasi and Refay, 2010). Number of irrigations affected
the root length density and decreased irrigation frequency
increased the root length density (Quanqi et al., 2010). Soil
moisture deficit has significant effect on grain yield andwater use efficiency with increasing soil moisture deficit*Email: honi.any@gmail.com© 2015, Soil Science Society of Pakistan (http://www.sss-pakistan.org)

Regulated deficit irrigation and evapotranspiration

reducing the yield of wheat but increasing the water use
efficiency (Mahamed et al., 2011, Hamed et al., 2015).
The second most important factor which affects thewater use efficiency is the evapotranspiration (ET) which
consists of evaporation from soil surface and transpirationfrom plant. Statistically non-significant difference in ET
was observed when single irrigation was applied at jointing,two irrigations at jointing and heading and three irrigations
at jointing-heading-milking stages (Quanqi et al., 2010; Duet al., 2010). Around 20% of applied water was lost fromsoil through evaporation. So 40% of the applied water canbe saved form loss through evaporation with two time
partial root zone irrigation (Tang et al., 2010). They also
reported that only 48-57% applied water was used intranspiration by crop during all irrigation practices. The
water required for highest wheat yield was 300 mm with ET
value 426 mm. Above this value of ET, irrigation
requirement increased without increase in yield (Sun et al.,2006). The wheat grain yield increased when observed ET
ranged from 415 to 460 mm. After that decline in yield wasobserved (Zhang et al., 2005). They also observed 16%
reduction in ET with 59 mm less irrigation under regulated
deficit irrigation. Irrigation significantly influenced thetranspiration, evaporation and canopy temperature of wheat
crop. ET was significantly increased with increasing
amount of water applied and number of irrigations (Xue etal., 2003; Qiu et al., 2008; Gao et al., 2014). The water use
efficiency had quadratic relation with ET and it decreased
with increasing the volume of irrigation (Li et al., 2003).
The crop coefficient (Kc) is the most important factor
in proper irrigation management. This is mostly used toestimate the crop water requirement and irrigation
scheduling (Ko et al., 2009). In Pakistan, there is no workon the evaluation of crop coefficient developed Doorenbos
and Pruitt (1977). This methodology provides simple tool
for the prediction of crop evapotranspiration (ETc) andguide for irrigation scheduling. The determination of Kc
using the on-site microclimatic data enables to calculate thecrop water use and propagation of this information to thefarmers in a trustworthy, serviceable and cheap manner.
Under regulated deficit irrigation, potassium (K)fertilization increase crop tolerance to water stress byutilizing the soil moisture more efficiently than in K
deficient plants. The increase in the stress tolerance by K
fertilization may be due to promotion of root growth
associated with more nutrient and water uptake (Umar andDin, 2002) and through the reduction of transpirational
water loss. It also maintains the osmotic and turgor of thecell and regulates the stomatal functioning under water
stress condition (Kant and Kafkafi, 2002), which isreflected in improved crop yield under drought conditions.

157

Under stress condition, K application promotes
photosynthetic rate, plant growth and yield (Egila et al.,
2001; Umar and Din, 2002).
Keeping in view the above facts, this study was
conducted for assessing yield and WUE under regulated
deficit irrigation at three levels of potassium that was K 0: 0
kg ha-1 K2O, K1: 200 kg ha-1 K2O and K2 : 300 kg ha-1 K2O,
respectively, and to calculate the Kc and ETa value forwheat crop at different stages.

Materials and Methods
Pot experiments were conducted at the experimental
farm of the Institute of Soil and Environmental Sciences,
University of Agriculture, Faisalabad, Pakistan (Latitude,
31°-26' N and 73°-06' E, 184 m ASL) during the winterseasons of 2010-11 and 2011-12. The climate of the study
area is semi subtropical-arid with more than 70% of theannual rainfall occurring during June to September. Plastic
pot having capacity of 9 kg soil was used as weighing
lysimeter. Each pot had 25 and 11cm height and radius,
respectively. Data showed (Table 1) that the soil type used
for filling pot as well-drained Hafizabad sandy clay loam,
mixed, semi-active, isohyperthermic Typic Calciargids. The
bulk density of soil was maintained as 1.41 Mg m-3 during
pot filling. The soil organic content was 0.52%. Retention
capacity of soil was measured by determining watercontents at pre-defined matric potential (Dane andHopmans, 2002) with the help of suction plates at 0.3, 0.6,
1.0, 3.0 and 4.5 bar pressure and a linear regression
equation was determined by taking ln (h) versus ln θ/θs to
get water contents at permanent wilting point (θWP) andfield capacity (θFC) of different soils (Williams et al., 1983).
The following equation was developed by taking ln θ/θs
versus ln (h) to get θWP, θFC, θAWC etc.
ln P = ln Pα + b ln (ϑ/ ϑs)(1)

P is the matric potential (k Pa), “P e” (intercept) is air entry
value/bubbling pressure which is inversely related to “α”, and “b”
is the slope of ln P vs ln θ/θs of water retention curve.

The linear relationship between ln θ/θs [-] and ln (P)[kPa] were observed for the experimental soil with an air
entry value (intercept) 0.0933 and a negative slope -7.9612(Figure 1). Some selected physical and water retention
properties of the soil are presented in Table 1.
Pot experiment was laid out in CRD having two factors(Regulated deficit irrigation X Potassium fertilizer) with
two factorial arrangements. Three regulated deficit
irrigation (RDI) treatments designed to subject the wheat
crop to various levels of soil water deficit at different stagesof crop growth and development were established andpotassium fertilizer was also applied according to theSoil Environ. 34(2): 156-165, 2015

Imran, Anwar-Ul-Hassan, Iqbal, Ullah and Šimunek

158

Table 1: Measured soil physical and hydraulic parameters of the experimental Soil
Particle size fraction (%)
BD
θs
θFC
θPWP
θAWC
Ks
sand
silt
clay*
(Mg m-3) ------------------cm3 cm-3------------------------------ Cm day-1
52.09±0.16 22.33±0.13 25.58±0.16 1.41±0.03 0.463±0.03 0.288±0.01 0.164±0.03 0.124±0.04 32±1.8

SOC(%)
0.52±0.01* Texture was loam according to USDA system ¶Mean± standard error (data are average of three repeats)

Table 2: Treatments (Irrigation and potassium levels) applied to the experimental units during the 2010-11 and2011-12Treatment
T1
T2
T3
T4
T5
T6
T7
T8
T9

Potassium Level Irrigation Level**
K0: NoI1 (HMLML)
potassium
I2 (MLLHM)
I3 (MMHMH)
K1: 200 kg ha-1
I1 (HMLML)
K2O
I2 (MLLHM)
I3 (MMHMH)
K2:300 kg ha-1
I1 (HMLML)
K2O
I2 (MLLHM)
I3 (MMHMH)

Jointing*
80 - 100
70 - 80
70 - 80
80 - 100
70 - 80
70 - 80
80 - 100
70 - 80
70 - 80

Booting
70 - 80
60 - 70
70 - 80
70 - 80
60 - 70
70 - 80
70 - 80
60 - 70
70 - 80

Heading
60 - 70
60 - 70
80 - 100
60 - 70
60 - 70
80 - 100
60 - 70
60 - 70
80 - 100

Filling
70 - 80
80 -100
70 - 80
70 - 80
80 -100
70 - 80
70 - 80
80 -100
70 - 80

Maturity
60 - 70
70 - 80
80 - 100
60 - 70
70 - 80
80 - 100
60 - 70
70 - 80
80 - 100*

The growing season was divided into six periods such as early development stage: germination (0-15 DAS), middle development
stage: jointing (15-45DAS), late development stage: booting (45-60 DAS), early reproductive stage: heading (60-90DAS), middle
reproductive stage: Grain filling (90-112 DAS) and late reproductive stage: Maturity stage (112-140 DAS). DAS stand, for days aftersowing.
** Soil moisture of no- soil- water- deficit (H), medium soil water deficit (M) and severe water deficit (L) was maintained at above
mentioned stages. When soil moisture varied out of the designed range, water was applied immediately to the top of the range. The
designed range were H (80-100 % of AWC) 80% of AWC is lower range and 100% of AWC is upper for this treatment. Similarly inother two treatments M (70-80% of AWC) and L (60-70% of AWC). Below 60% of available water content moisture stress started
so treatment was designed above this limit.

treatment plan (Table 2: Description of treatments). Eachtreatment was replicated three times. During the two
growing seasons, controlled irrigation was applied to eachpot by weighing pot on daily basis using weighingbalance, so as to accurately maintain the soil water deficit
levels followed by the above experimental design. Locallymanufactured digital balance was used for weighing. It
had weighing capacity in range from 200-30000 + 5g.
Data was collected according to Dwyer et al. (1987) andthe irrigation amount was calculated to replace thedepleted water content from each pot according todesigned treatments. Local high yielding wheat variety
Sahar-2006 was planted. The sowing time was November
20, 2010 and November 25, 2011. Urea was applied at therate of 120 kg N ha -1 in two splits while phosphorus wasapplied at 85 kg ha-1 and potassium was applied according
to treatment plan at the time of sowing. Seedling density
after germination was controlled to 4 plants per pot. Weeds
were removed effectively by hand during both growing
seasons. Pests and diseases were also effectively controlled
by pesticides in time. All the plants were harvested on April
13 during 2010-11 and April 09 during 2011-12. Based on
soil water measurements from Pot by weighing method, theActual Evapotranspiration was calculated using waterbalance equation:

Soil Environ. 34(2): 156-165, 2015

Figure 1: Determination of soil water characteristic
curve of the experimental soil
ETa  ( I  p)  S (1)where ETa is the actual evapotranspiration (mm), I(mm) is irrigation, p (mm) is rainfall, and ΔS (mm) ischange in root zone storage. There was no excess water
losses below the root zone because the calculated volume ofirrigation was applied in the root zone and pots were closed
at the bottom. The crop coefficient was calculated asfollows:

Regulated deficit irrigation and evapotranspiration

Kc = ETa / ET0 (2)where ETa and ET0 stand for the actual
evapotranspiration and potential evapotranspiration of thespecific stage for which Kc was calculated. Daily
reference/potential evapotranspiration (ET 0) for ahypothetical crop (Figure 2) was calculated using thePenman-Monteith FAO-56 Equation (Allen et al., 1998) as
follows:

900
u 2 (es  ea )Tmean  273
   (1  0.34u 2 )0.408( Rn  G)  
ET0 

(3)

where ET0 is the reference/potential evapotranspiration(mm day-1), Rn the net radiation reaching the crop surface(M Jm-2 day-1), G the soil heat flux density (MJ m-2 day-1), γ
is the psychometric constant (k Pa °C-1), Tmean the average
daily air temperature measured at 2 m height (°C), u2 thewind speed at 2 m height (m s-1), es-ea the saturation vapour
pressure deficit (k Pa), ea the actual vapour pressure (k Pa),es the saturation vapour pressure (k Pa) and ∆ the slope ofthe vapour pressure curve (k Pa °C-1).

Figure 2: Determination of potential evapotranspirationof experimental area during 2010-11 (y1) and2011-12 (y2)At the end of growing seasons (April 13, 2011 andApril 9, 2012), each pot was harvested for biomass, grain
yield, root length density and root mass density. Harvest
index was calculated as grain yield divided by mature crop
biomass. Water-use efficiency was calculated as follows(Hussain et al., 1995):

WUE 

GY (4)
ETa

Where WUE (kg m-3) is the water use efficiency forgrain yield, GY is the grain yield (kg) and ET a (m3) is theactual evapotranspiration. Differences between treatments

159

were examined using ANOVA (R-Software). The degree ofassociation between different traits was also estimatedthrough linear or non-linear regression models of the same
statistical package.

Results
Grain yield, actual evapotranspiration andwater use efficiency of wheat
The regulated deficit irrigation had significant effect on
grain yield, seasonal actual evapotranspiration (ETa) andwater use efficiency (WUE) with or without potassium
fertilizer application (Table 3). Compared to the I1(HMLML) in combination with K0 (No potassium wasapplied), regulated soil water deficit treatment along with orwithout potassium application improved the grain yield.
The treatment combination I3 (MMHMH) in combination
with K2 (K2O at 300 kg ha-1) showed the highest increase in
grain yield that was 21.38 and 25.45% over I1 (HMLML)
along with K0 (No potassium), respectively, in growing
seasons 2010-11 and 2011-12. The second best treatment
was again I3 (MMHMH) in combination with K1 (K2O at
200 kg ha-1) that showed 18.36% increase in 2010-11 and15.37% increase in 2011-12 over T1 (HMLML) in
combination with K0 (No potassium). In this study, thehighest grain yield was attained in treatment T 9 (MMHMH)
in combination with K2 (K2O at 300 kg ha-1) which was
subjected to medium soil water deficit at the jointing,booting and filling stages while no soil water deficit at theheading and maturity stage. Three linear functions werefitted through regression analysis among the data fromgrain yield, total biomass and harvest index under regulated
deficit irrigation (Table 4) while regression analysis was
non-significant in case of interaction of regulated deficit
irrigation and potassium and main effect of potassium.
Grain yield increased linearly with the biomass and harvest
index, and increase in both biomass and harvest index under
different levels of regulated deficit irrigation was result of
the increase in both total biomass and harvest index.
In case of seasonal actual evapotranspiration (Table 3), theETa ranged from 206.8-235.1 and 219.7-250.5 mm,
respectively, during 2010-11 and 2011-12 in winterseasons. The maximum Eta was observed in treatment I1(HMLML) in combination with K2 (K2O at 300 kg ha-1) in
2010-11 while I3 (MMHMH) in combination with K2(Potassium at 300 kg ha-1) showed the highest ETa in 201112 but both treatments were statistically at par during both
years.
Significances occurred in water use efficiency(WUE) between regulated deficit treatments incombination with different levels of potassium. It wasobserved from the data presented in Table 3 that the

Soil Environ. 34(2): 156-165, 2015

Imran, Anwar-Ul-Hassan, Iqbal, Ullah and Šimunek

160

Table 3: Grain yield, Biomass and harvest index of wheat subject to various treatments under pot experiment
during 2010-11 and 2011-12
Treatment
I1 (HMLML)
I2 (MLLHM)
I3(MMHMH)
LSD(p≤ 0.05)
I1 (HMLML)
I2 (MLLHM)
I3(MMHMH)
LSD(p≤ 0.05)

Grain yield (Mg ha-1)
Ko
K1
K2
1.87

1.92

2.00

1.96
2.13

2.02
2.21
0.27

2.10
2.27

1.82
1.91
2.02

1.90
2.00
2.10
0.12

1.92
2.02
2.28

Actual evapotranspiration (mm)Ko
K1
K2
2010-11
218.8
230.6
235.1
206.8
210.5
213.7
222.8
228
234
0.55
2011-12
232.8
245.7
250.5
219.7
224.4
227.6
240.2
245.3
251.7
0.59

Water use efficiency (kg m-3)
Ko
K1
K2
0.94

0.92

0.94

1.04
1.05

1.06
1.07
0.03

1.09
1.07

0.86
0.96
0.93

0.85
0.98
0.94
0.04

0.84
0.98
1.00

Table 4: Relationship of different variables under regulated deficit irrigation
Water Use Efficiency
Harvest Index
Biomass
Root mass density
Root length density

Yield
0.74**(0.03)
0.86*(0.04)
0.96*(0.00)
0.89*(0.02)
0.88*(0.02)WUE

HI

Biomass

RMD

0.96*(0.001)
0.57**(0.02)
0.97*(0.01)
0.98*(0.03)

0.68(0.03)
0.97*(0.01)
0.96*(0.01)

0.72*
0.03
0.72*
(0.03)

0.97*(0.001)*Liner relationship, **Quadratic relationship, Upper values are R2 values, Values in parenthesis are probability value at alpha 0.05

WUE values varied from 0.84 to 1.09 Kg m-3 in two years(2010-11 and 2011-12). The increase in WUE wasobserved (10.6-13.8 and 11.6-16.3%) with regulated
deficit irrigation Treatments I 2 (MLLHM) and I 3(MMHMH) in combination with K 0, K1 and K2 as
compared to the I 1 (HMLML) in combination with K 0,
respectively, during 2010-11 and 2011-12. While 0-2.1
and 1.2-2.3% decrease in WUE was recorded in RDI
treatment I1 (HMLML) in combination with K 1 and K2,
respectively, in growing seasons 2010-11 and 2011-12.
The maximum WUE was recorded in treatment I 2(MLLHM) and I 3 (MMHMH) in combination with K2
which was 1.09 and 1.0 kg m-3 respectively in growing
seasons 2010-11 and 2011-12 and both were statisticallyat par during both years.
The good relationship between WUE and the harvest
index was linear while relationships between WUE andgrain yield, biomass were quadratic under regulated deficit
irrigation (Table 4). In our simulation, the highest WUE of
1.036 kg m-3 was attained as the grain yield approached thecritical value of 9.01 g per pot around the 68.33% of theSoil Environ. 34(2): 156-165, 2015

observed maximum grain yield. The simulated value of
WUE was lower as compared to observed value. The results
indicated that the maximum WUE was not recorded at the
maximum grain yield but a little earlier before that. The
WUE increased significantly with the increase in harvest
index. It was also significantly increased with increase in
grain yield until the critical value mentioned above
occurred, followed by a condign decrease of WUE withincrease in grain yield. Similar trend was observed inbiomass and WUE relationship. At a low value of grain
yield and biomass, WUE almost linearly increased until arelatively higher WUE was met, after which being amarginal increase of WUE till the critical values of grain
yield and biomass reached.

Cropcoefficient(Kc)andactualevapotranspiration (ETa) of wheat at six
stagesSignificant differences occurred among treatments
regarding crop Kc and ETa at jointing, booting, heading,grain filling and maturity stages (Table 5 and 6). In 2010-

Regulated deficit irrigation and evapotranspiration

161

Table 5: Crop coefficient (Kc) of wheat subject to various treatments at six stages under pot experiment during
2010-11 and 2011-12
Treatment Potassium Irrigation
Grain
Germination Heading
Jointing
Booting Maturity
levelslevelsfilling
2010-11T1
K0
I1 (HMLML)
0.56
1.07
0.9
0.84
0.86
0.45
T2
K1
I2 (MLLHM)
0.54
1.13
0.55
0.74
1.12
0.44
T3
K2
I3(MMHMH)
0.56
1.13
0.57
1.05
1.12
0.44
T4
K0
I1 (HMLML)
0.57
1.17
0.92
0.85
1.15
0.45
T5
K1
I2 (MLLHM)
0.55
1.17
0.56
0.75
1.15
0.44
T6
K2
I3 MMHMH)
0.57
1.17
0.58
1.06
1.15
0.45
T7
K0
I1 (HMLML)
0.58
1.22
0.93
0.86
1.18
0.45
T8
K1
I2 (MLLHM)
0.56
1.18
0.57
0.76
1.16
0.45
T9
K2
I3(MMHMH)
0.58
1.22
0.59
1.08
1.17
0.46
LSD (p≤ 0.05)
ns
0.011
0.04
0.011
0.02
0.01
2011-12T1
K0
I1 (HMLML)
0.57
1.09
0.92
0.86
0.88
0.46
T2
K1
I2 (MLLHM)
0.55
1.15
0.56
0.75
1.14
0.45
T3
K2
I3(MMHMH)
0.57
1.15
0.58
1.07
1.14
0.45
T4
K0
I1 (HMLML)
0.58
1.19
0.94
0.87
1.17
0.46
T5
K1
I2 (MLLHM)
0.56
1.19
0.57
0.77
1.17
0.45
T6
K2
I3 MMHMH)
0.58
1.19
0.59
1.08
1.17
0.46
T7
K0
I1 (HMLML)
0.59
1.24
0.95
0.88
1.2
0.46
T8
K1
I2 (MLLHM)
0.57
1.2
0.58
0.78
1.18
0.46
T9
K2
I3 MMHMH)
0.59
1.24
0.6
1.1
1.19
0.47
LSD (p≤ 0.05)
ns
0.01
0.06
0.01
0.03
0.01
11 growing season, crop coefficient (Kc) and actual
evapotranspiration (ETa) ranged from 0.55-0.93, 20.6-34.8
mm, 0.86-1.18, 13.9-19.1 mm, 1.07-1.22, 60.7-69.2 mm,
0.74-1.08, 35.4-51.7mm and 0.44-0.0.46, 55.6-58.1 mm
respectively, at jointing, booting, heading, grain filling andmaturity stage. The maximum Kc was recorded in I1(HMLML) in combination with K2 (K2O at 300 kg ha-1) atjointing stage because 80-100 % of available water content
was applied at this stage which promoted the full expansionof leaf and unlimited supply of water. So highest actual
evapotranspiration was also occurred in this treatment at
jointing which is the reason of highest Kc. At booting
stages, Kc and ETa was statistically at par in regulated
deficit irrigation Treatment I1 (HMLML) and I3 (MMHMH)
while former was significantly differed from the I2(MLLHM) because at these stages I1 (HMLML) and I3(MMHMH) received 70-80% of available water content.
However, I2 (MLLHM) received 60-70% of available watercontent. So the difference in water supply was expressed as
difference in ETa and Kc. At heading stage, Kc and ETa
was the maximum because crop attained its maximum
height and full leaf development.
Regardless of the applications of water, plant extracts
the available water content in 60-70% or above range tofulfill the demand of evapotranspiration. After heading
stage, decline in crop coefficient (Kc) and actual
evapotranspiration was observed and both parameters
decreased at grain filling stage. However, the highest Kc
and ETa was observed in regulated deficit treatment I3(MMHMH) in combination of all three levels of potassium
as compared to the other treatments at grain filling stage
because of more evapotranspiration in this treatment, might
be due to slowl yellowing of leaves as visual difference
noted between treatments at this stage. At maturity stage,
actual evapotranspiration was reduced and potential
evapotranspiration increased which result low Kc value.
More than 80% leaves were wilt and photosynthesis
stopped due to stomata closer. As can be seen from Table 5
and 6, similar trend was observed in crop coefficient andactual evapotranspiration in 2011-12 growing seasons.

Root mass (g cm-3) and length density (cmcm-3)
Root mass and length density of wheat wassignificantly affected by irrigation and potassium levels
during 2010-11 and 2011-12 (Table 7). Root massdensity ranged from 0.76-1.02 and 0.73-1.0 g cm-3,
respectively, in growing seasons 2010-11 and 2011-12.
The root mass was increased with regulated deficit

Soil Environ. 34(2): 156-165, 2015

Imran, Anwar-Ul-Hassan, Iqbal, Ullah and Šimunek

162

Table 6: Evapotranspiration (ETa) mm of wheat subject to various treatments at six stages under pot experiment
during 2010-11 and 2011-12
Treatment Potassium
Irrigation
Grain
Germination Heading Jointing
Booting Maturity
levelslevelsfilling
2010-11
T1
K0
I1(HMLML)
13.4
60.7
33.7
40.2
13.9
56.9
T2
K1
I2 MLLHM)
13
64.1
20.6
35.4
18.1
55.6
T3
K2
I3(MMHMH)
13.4
64.1
21.3
50.3
18.1
55.6
T4
K0
I1 (HMLML)
13.7
66.3
34.4
40.7
18.6
56.9
T5
K1
I2 (MLLHM)
13.2
66.3
20.9
35.9
18.6
55.6
T6
K2
I3 MMHMH)
13.7
66.3
21.7
50.8
18.6
56.9
T7
K0
I1 (HMLML)
13.9
69.2
34.8
41.2
19.1
56.9
T8
K1
I2 (MLLHM)
13.4
66.9
21.3
36.4
18.8
56.9
T9
K2
I3(MMHMH)
13.9
69.2
22.1
51.7
19
58.1
LSD (p≤0.05)
0.04
0.11
0.18
0.19
0.05
0.22
2011-12T1
K0
I1 (HMLML)
13
62.1
34
51.7
17.2
54.8
T2
K1
I2 (MLLHM)
12.5
65.6
20.7
45.1
22.2
53.6
T3
K2
I3(MMHMH)
13
65.6
21.5
64.3
22.2
53.6
T4
K0
I1 (HMLML)
13.2
67.8
34.8
52.3
22.8
54.8
T5
K1
I2 (MLLHM)
12.8
67.8
21.1
46.3
22.8
53.6
T6
K2
I3 MMHMH)
13.2
67.8
21.8
64.9
22.8
54.8
T7
K0
I1 (HMLML)
13.5
70.7
35.2
52.9
23.4
54.8
T8
K1
I2 (MLLHM)
13
68.4
21.5
46.9
23
54.8
T9
K2
I3(MMHMH)
13.5
70.7
22.2
66.1
23.2
56
LSD(p≤0.05)
0.01
0.11
0.17
0.25
0.06
0.21
Table 7: Root mass density and root length density of wheat subject to various treatments under pot experiments
during 2010-11 and 2011-12
Treatment
I1 (HMLML)
I2 (MLLHM)
I3(MMHMH)
LSD(p≤ 0.05)
I1 (HMLML)
I2 (MLLHM)
I3(MMHMH)
LSD (p≤ 0.05)

Root mass density (g cm-3)
Ko
K1
K2
2010-11
0.76
0.92
0.95
0.78
0.95
0.97
0.82
0.99
1.02
0.083
2011-2012
0.73
0.76
0.88
0.76
0.8
0.93
0.8
0.96
1
0.052

irrigation treatment in combination with three levels of
potassium which ranged from 2.6 to 34.2 and 4.1 to 37.0
% as compared to regulated deficit irrigation treatment I1(HMLML) in combination with K0 (No potassium wasapplied) in growing season 2010-11 and 2011-12,
respectively. The regulated deficit irrigation treatment I3(MMHMH) in combination with K2 (K2O at 300 kg ha-1)
showed the highest root mass density which was 34.2 andSoil Environ. 34(2): 156-165, 2015

Root length density (cm cm-3)
Ko
K1
K2
2.17
2.23
2.34

2.61
2.7
2.84
0.074

2.71
2.77
2.91

2.07
2.18
2.28

2.17
2.28
2.75
0.079

2.51
2.64
2.85

37.0% more as compared to regulated deficit irrigation
treatment I1 (HMLML) in combination with K0,
respectively, in growing seasons 2010-11 and 2011-12.
Such performance in root mass density was extremely
similar to that root length density. Regulated deficit
irrigation treatment in combination with three levels of
potassium improved the root length density as compared toregulated deficit irrigation treatment I1 (HMLML) inRegulated deficit irrigation and evapotranspiration

combination with K0 in growing seasons 2010-11 and 201112. The treatment combination I3 (MMHMH) in
combination with K2 (K2O at 300 kg ha-1) showed thehighest increase in root length density that was 34.1 and37.7 % over I1 (HMLML) in combination with K0 ingrowing seasons 2010-11 and 2011-12, respectively. In thisstudy, the highest root mass and length density wereattained in treatment I3 (MMHMH) in combination with K 2(K2O at 300 kg ha-1) which was subjected to medium soil
water deficit at the jointing, booting and filling stages while
no soil water deficit at the heading and maturity stage.
Root mass and length density increased linearly with
the WUE and harvest index, and increase in both under
different levels of regulated deficit irrigation was result of
the increase in WUE and harvest index. Biomass and grain
yield also linearly increased with the root mass and lengthdensity. The root mass density was also increased linearlywith increase in root length density (Table 4).

Discussion
Grain yield was maximum in the regulated deficit
irrigation treatment I3 (MMHMH) in combination with K2(K2O t 300 kg ha-1) as compared to I1 (HMLML) in
combination with K0 (No potassium was applied) ingrowing seasons 2010-11 and 2012. Since the highest grain
yield was maintained in the regulated deficit irrigation
treatment I3 (MMHMH) in combination with K2 (K2O at
300 kg ha-1), we assured that the optimum controlled soil
water deficit treatment in this study would be: 70-80% of
AWC at the jointing, booting and grain filling stage and 80100% of AWC at heading and maturity in combination of
Potassium (K2O) at the rate of 300 Kg ha-1 and it was
followed by K2O level 200 Kg ha-1. Thus, water resources
could be scientifically saved through regulated deficit
irrigation in combination with potassium without reductionof crop yield under semi-arid condition like Pakistan. Such
results are in line with that from Alderfasi and Refay (2010)
who reported that the irrigation at 100 and 150 mm of CPE
was statistically at par with regard to growth characters andK rates influenced growth vigor mostly through leaf areaand dry matter production. Work of Zhang et al. (2006) also
supported the results of current study. The conclusions
could be helpful for the sustainable agriculture development
in arid and semi-arid regions of the world especially incountry like Pakistan which has low per capita water
availability.
There were significant differences among treatments I1(HMLML) with or without potassium and the regulated
deficit treatment I2 (MLLHM) and I3 (MMHMH) with orwithout potassium in water use efficiency (WUE). Our
results are in line with Du et al. (2010) who found that
WUE enhanced by applying water deficit at planting–stem

163

elongation stage. Water deficit at planting–stem elongation
stage is the best choice for improved WUE and its
increment also decreased with deficit irrigation. Severe
water scarcity at seedling–stem elongation, stem
elongation–booting and booting–milking reduced by 5.61,
9.25 and 10.07% WUE, respectively. Mild water deficit
produced 21.5 % more grain yield at seedling–stem
elongation and milking–harvesting stage but it decreased
WUE by 3.22 and 3.64% (Quanqi et al., 2010; Karrou etal., 2012).
Crop coefficient (Kc) value of wheat was obtained by
dividing the actual evapotranspiration (ETa) with potential
evapotranspiration (ETp) and Kc and ETa both were
presented in Table 4 and 5. The Kc values increased from
germination to heading and this increase due to increase in
ETa value and low ETp value. After heading stage the Kc
value decreased gradually due to decrease in Eta andincrease in ETp. However, previous work showed that Kc
values varied by many factors such as location, seasons,crop height and management (Baille, 1996, Marin et al.,2016). Our results are also supported by those of Doorenbos
and Pruitt (1977) who divided the crop coefficient (K c)curve into four stages: Initial, crop development, mid andend-season stages. Similarly, Li et al. (2003) calculated Kc
values 0.55, 1.03, 1.19, and 0.65 for the initial, cropdevelopment, mid-season, and late-season stages,
respectively. In other study, Kc values determined over thegrowing seasons varied from 0.1 to 1.7 for wheat (Ko et al.,2009). They reported that the development of regionallybased and growth-stage-speciﬁc Kc helps in irrigation
management and provides precise water applications.
Evapotranspiration, an important aspect of water balance
and a key factor to determine proper irrigation schedule andto improve water use efficiency in irrigated agriculture (Liuet al., 2002).
Root length and mass density are important parameterswhich determine the water and nutrient uptake from soil.
Our results showed that the application of 70-80% available
water at jointing, booting and grain filling stages and 80100% of available water at heading and maturity in
combination with potassium significantly enhanced the root
length and mass density. Such results coincided with thesefrom Xue et al. (2003) who reported that irrigation
significantly affected the rooting pattern. They also
observed increase in root length density with 3 times
irrigation at jointing, heading and milking stage in soil
profile < 30 cm depth. The highest root length density wasobserved in soil profile > 30 cm depth with single irrigation
at jointing stage (Quanqi et al., 2010). Previous studies also
showed that soil drying at early stage stimulated root
growth, particularly the root growth in the deeper soil
profile (Zhang et al., 1998).

Soil Environ. 34(2): 156-165, 2015

Imran, Anwar-Ul-Hassan, Iqbal, Ullah and Šimunek

164

The relationship between harvest index and grain yield,
biomass, WUE, root length density, root mass density werelinear under regulated deficit irrigation. So were between
biomass and grain yield, WUE and root length density, root
mass density; root length density and grain yield, biomass;root mass density and grain yield, biomass; root lengthdensity and root mass density. However, the relationshipbetween WUE and grain yield, biomass could be describedby quadratic equations. These relationships predicted thatthe highest harvest index was associated with the maximum
grain yield, biomass, WUE, root length and mass density
while the maximum WUE was not associated with thehighest grain yield and biomass which was controlled bysoil moisture content and water consumption. However,
because of different experimental conditions from theprevious studies such conclusions above were partly
supported by Zhang et al. (1998) and Kang et al. (2002).
While the positive correlation of root weight density(RWD) and root length density (RLD) with proper
irrigation (Sangakkara et al., 2010) is evident from manystudies.

Conclusion
In most of the cases of seasonal drought or arid andsemi-arid areas of the world, regulated deficit irrigation in
combination with potassium has significant effect on yield
increase and improving water use efficiency. This research
explores the effectiveness of regulated deficit irrigation in
combination with potassium on wheat in semi-arid
environment. The optimum level of regulated deficit
irrigation proved to be 70-80% of available water content at
middle vegetative growth period (Jointing), the latevegetative periods (booting), middle reproductive period(grain filling) and 80-100% of available water content at theearly reproductive period (heading), and late reproductive
period (maturity), respectively, in combination withpotassium at the rate of 300 Kg ha-1.
The corresponding optimum actual evapotranspirationof 242.9 mm (average of two years to give a fullconsideration of the climatic variability) was distributed asfollowing: 13.7 mm during germination stage, 22.15 mm
during the middle vegetative stage (jointing), 21.10 mm
during the late vegetative stage (booting), 69.95 mm during
the early reproductive stage (heading), 58.9 mm during the
middle reproductive stage (grain filling) and 57.05 mm
during the late reproductive stage (maturity).

Acknowledgments
This research was fully funded by Higher Education
Commission Pakistan under the Indigenous 5000 MS
leading to Ph. D program at Institute of Soil andSoil Environ. 34(2): 156-165, 2015

Environmental
Faisalabad.

Sciences,

UniversityofAgriculture

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