Effect of mulching on soil and plant water status, and thegrowth and yield of wheat (Triticum aestivum L.) in asemi-arid environment

Debashis Chakraborty a,*, Shantha Nagarajan b, Pramila Aggarwal a, V.K. Gupta a,R.K. Tomar a, R.N. Garg a, R.N. Sahoo a, A. Sarkar c, U.K. Chopra a,K.S. Sundara Sarma a, N. Kalra a

aDivision of Agricultural Physics, Indian Agricultural Research Institute, New Delhi 110012, IndiabNuclear Research Laboratory, Indian Agricultural Research Institute, New Delhi 110012, Indiac Indian Agricultural Statistics Research Institute, New Delhi 110012, India

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 4

a r t i c l e i n f o

Article history:

Received 24 October 2007

Accepted 2 June 2008

Published on line 9 July 2008

Keywords:

Mulch

Wheat

Soil temperature

Canopy air temperature difference

Root length density

Water use efficiency

a b s t r a c t

Mulching is one of the important agronomic practices in conserving the soil moisture and

modifying the soil physical environment. Wheat, the second most important cereal crop in

India, is sensitive to soil moisture stress. Field experiments were conducted during winter

seasons of 2004–2005 and 2005–2006 in a sandy loam soil to evaluate the soil and plant water

status in wheat under synthetic (transparent and black polyethylene) and organic (rice husk)

mulches with limited irrigation and compared with adequate irrigation with no mulch

(conventional practices by the farmers). Though all the mulch treatments improved the soil

moisture status, rice husk was found to be superior in maintaining optimum soil moisture

condition for crop use. The residual soil moisture was also minimum, indicating effective

utilization of moisture by the crop under RH. The plant water status, as evaluated by relative

water content and leaf water potential were favourable under RH. Specific leaf weight, root

length density and dry biomass were also greater in this treatment. Optimum soil and

canopy thermal environment of wheat with limited fluctuations were observed under RH,

even during dry periods. This produced comparable yield with less water use, enhancing the

water use efficiency. Therefore, it may be concluded that under limited irrigation condition,

RH mulching will be beneficial for wheat as it is able to maintain better soil and plant water

status, leading to higher grain yield and enhanced water use efficiency.

# 2008 Elsevier B.V. All rights reserved.

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1. Introduction

Effect of mulching on conserving moisture and increasing

productivity of crops had been reported in maize (Zhang et al.,

2005), wheat (Verma and Acharya, 2004a,b; Li et al., 2005;

Huang et al., 2005; Rahman et al., 2005), vegetables (Ramalan

and Nwokeocha, 2000; Araki and Ito, 2004; Incalcaterra et al.,

* Corresponding author. Tel.: +91 11 25841178/8853.E-mail addresses: debashis@iari.res.in, debashisiari@hotmail.com

0378-3774/$ – see front matter # 2008 Elsevier B.V. All rights reservedoi:10.1016/j.agwat.2008.06.001

2003) and other crops (Tariq et al., 2001; Kumar et al., 2003;

Haq, 2000; Kar and Singh, 2004) and also in bare plots (Farrukh

and Safdar, 2004; Giordani et al., 2004). Mulch has the potential

to control weed growth (Erenstein, 2002) and retain soil

moisture (Dalrymple et al., 1992; Manakul, 1994; Enrique et al.,

1999). Combination of irrigation with mulch technology is

advocated for better uptake of water by the spring wheat (Li

(D. Chakraborty).

d.

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 41324

et al., 2004) and to reduce the number of irrigation (Mandal and

Ghosh, 1984). These results have strongly established that the

conserved moisture through mulching have been very

effective to plants during stress.

However, the quantification in terms of growth attributes

and soil–plant–water relationships in wheat under mulch

have not been substantiated. Wheat (Triticum aestivum L.) is the

most important rabi cereal crop in the north India. India is the

second largest producer of wheat, but there has been

significant yield stagnation since 1999–2000 (Nagarajan,

2005). This crop is highly sensitive to moisture and thermal

stress. In many parts of the region, it is cultivated as a rainfed

crop, particularly in the semi-arid tracts of central and

peninsular India. Even in irrigated areas, the availability of

assured water for irrigation has become limited. Under rainfed

situation, maintaining favourable soil moisture in root zone is

necessary for continued growth and yield of wheat. Among

various agronomic measures, mulching may be one of the

suitable method to maintain optimum moisture and thermal

environment in soil, increase water use efficiency through

reduction in evaporation and subsequently higher grain yield.

The mulch also varies widely in terms of the material used

and their differential effects in producing the hydrothermal

regimes in soil and plant. Information is scanty on the

comparative effect of organic and plastic mulches under the

same crop with similar type of agro-environment. Therefore, a

study was conducted in a sandy loam soil under semi-arid

environment of Delhi, India, to evaluate the soil and plant

water status in wheat under different types of mulches. In our

experiment, as the water retention parameters were to be

compared with respect to soil water status at similar growth

stages of the crop, mulching was done after emergence so that

the phenology of the crop is nearly the same in all treatments.

2. Materials and methods

2.1. Study area

Field experiments were conducted during rabi (winter) 2004–

2005 and 2005–2006 at the Research Farm of the Indian

Table 1 – Weather conditions during the period of study

Months Meantemperature (8C)

Rainfall(mm)

2004–2005

November 19.8 0

December 15.1 0

January 12.8 2.2

February 15.5 32.2

March 22.6 13.4

April 27.6 4.8

2005–2006

November 19.3 0

December 12.7 0

January 13.5 3.2

February 20.0 0

March 21.0 17.8

April 28.2 2.8

Agricultural Research Institute, New Delhi, India (77890N,

288370E, 228.7 m asl) with wheat (T. aestivum, L.) as the test

crop. The climate is semi-arid with warm summer and mild

winter. Summers are long (early April–August) with the

monsoon setting in between (July–September). The soil is

sandy loam (Typic Haplustept) with medium to angular blocky

structure, non-calcareous and slightly alkaline in reaction.

The soil (0–30 cm) has bulk density 1.56 Mg m�3; hydraulic

conductivity (saturated) 1.05 cm h�1, saturated water content

(0.42 m3 m�3; pH (1:2.5 soil/water suspension), 7.4; EC,

0.34 dS m�1; organic C, 0.3 g kg�1; total N, 0.031%; available

(Olsen) P, 6.9 kg ha�1; available K, 279.0 kg ha�1; sand, silt and

clay, 71.7, 12.0 and 16.3%, respectively. Available soil moisture

ranged from 25–28% (field capacity) to 8–10% (wilting point) for

0 to 0.9 m layers.

2.2. Weather

Mean monthly air temperature, pan evaporation, relative

humidity, sunshine hours and total rainfall during the period

of study are presented in Table 1. Monthly mean temperatures

were similar in both the years with December month being

slightly cooler and February month relatively warmer in 2005–

2006 compared to the previous year. Warmer February month

without rain resulted in higher atmospheric evaporative

demand (4.3 mm day�1) in 2005–2006 as compared to 2004–

2005 (2.7 mm day�1). More specifically, there was a sudden

increase in average temperature during third week of February

(20–26th), which was 2 and 3 8C more than the previous and

the following weeks, respectively. The average humidity was

similar for both the years and the sky was cloud free for most

of the time during crop growth period. Rainfall in the 1st year

(52.6 mm) was significantly higher and well distributed than

the 2nd year of experiment (23.8 mm).

2.3. Experimental design

The experiment was laid out in a randomized block design

with five treatments, namely, limited irrigation with no mulch

(I0M0), transparent polyethylene (I0MT), rice husk (I0MR),

black polyethylene (I0MB); and adequate irrigation with no

Pan evaporation(mm day�1)

Relativehumidity (%)

Sunshinehours (h)

2.8 62.6 6.3

2.1 69.8 2.6

1.8 72.0 3.8

2.7 67.1 6.4

4.7 60.2 7.4

6.7 38.3 8.1

2.6 63.5 6.8

1.8 67.2 4.1

2.4 65.2 5.8

4.3 67.2 6.4

4.6 64.8 7.1

8.3 54.7 8.3

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 4 1325

mulch (I1M0) as control, each replicated thrice. Black poly-

ethylene (BP) was not used during 2005–2006. The plot size was

3.5 m � 7.0 m. The thickness of polyethylene mulches was

400 mm. Rice husk (RH) was applied @ 8.0 Mg ha�1 (1 � 0.2 cm

thickness). For adequately irrigated plots, 60 mm of irrigation

water was applied at CRI, tillering, flowering and grain

formation stages whereas under limited water condition,

the same was applied at CRI and grain development stages.

Wheat (cv. PBW 343) was sown on 11th and 21st November in

2004 and 2005, respectively by a seed-cum-fertilizer drill (at a

depth of 4–5 cm), after a pre-sowing irrigation @ 100 kg seeds

ha�1. Mulches were applied after the seedling emergence (7–10

DAS) in between the rows, allowing plants to grow normally

and also ensuring that the rainwater could enter into the soil.

Urea was applied as a source of nitrogen @ 120 kg N ha�1 in

two equal splits, with minimum disturbance to mulching.

Single super phosphate and muriate of potash were applied as

basal @ 60 and 40 kg ha�1 P2O5 and K2O, respectively.

2.4. Sampling and measurements

The profile soil moisture (v/v) was monitored once in a week at

15 cm increments (up to 90 cm) by measuring gravimetrically

(drying method) and then multiplying with bulk density as

observed in field during the experiment. Soil water potential

(SWP) was monitored at 0–15 and 15–30 cm depth using

tensiometers installed in the field. Soil temperature at 7, 14, 21

and 28 cm depths was monitored using digital thermal probes

(Decibel, New Delhi) twice-a-day (10:00 and 14:30 h).

Second fully expanded leaf from top was randomly

collected every week from each experimental plot between

11.00 and 12.00 h and transferred quickly to the laboratory in a

moistened polythene bag for determining the relative water

content (RWC) and leaf water potential (LWP) of the crop.

Canopy temperature readings were taken using a hand-

held infrared thermometer (AG-42, Telatemp Corporation,

USA) before solar noon time. These values were summed up to

generate the cumulative stress degree day (CSDD) for the

entire crop growth period (Idso et al., 1977).

For determining RWC (Barr and Weatherley, 1962), the mid-

leaf section of about 5 cm2 was cut with sharp blade in the

laboratory, placed in a pre-weighed air-tight vial and weighed

to obtain leaf fresh weight (FW). Then the leaf sections were

floated in distilled water in a petri-dish under low light

conditions in the laboratory. After about 4 h, the leaf sections

were removed, blotted dry and re-weighed in the same vial to

obtain leaf turgid weight (TW). Then they were dried at

65 � 5 8C in an oven till constant weight and weighed with vial

to get the dry weight (DW). The RWC was determined using the

following formula:

RWC ð%Þ ¼ ðFW�DWÞðTW�DWÞ

� �� 100;

where FW is the fresh weight, TW is the turgid weight, and DW

is the dry weight.

LWP was measured using a pressure chamber (S-pms

Instruments, New Delhi, India) following the method of

Scholander et al. (1964).

Three plants were randomly selected from each plot, their

green leaves were separated and their area was measured with

a leaf area meter (model LICOR 3100). The leaves were oven-

dried at 65 � 5 8C to constant weight and the specific leaf

weight (SLW) was expressed as leaf weight per unit of leaf

area. The dry plant biomass was determined by drying the

stem part of the plant at 65 � 5 8C and adding it to the

respective leaf dry weight.

Root samples were collected at reproductive stage (65 days

after sowing, DAS) using core auger. The above ground plant

parts were removed and soil surface was removed of

unwanted plant materials. The core of the auger was placed

so as to keep the base of the stem at the center and then soil

core was excavated from each 15 cm depth layer down to a

150 cm depth. After the excavation, the soil cores were sealed

in polythene bags, brought to the laboratory, washed and

processed for scanning. The length of the cleaned, air-dried

roots from each depth was placed under WINRHIZO system

(Regent Instruments Inc., Canada) and lengths were recorded

through the scanning and image analysis of the root skeleton.

The root length was divided by the volume of the core, from

which root length density (RLD) was calculated for each soil

depth.

The crop was harvested on 15th and 13th April in 2005 and

2006, respectively and the grain yields were determined.

Water use efficiency for the cropping season was calculated

based on grain yield. The crop water use (or evapotranspira-

tion) was calculated from the soil water balance by taking

weekly soil moisture depletion values and the irrigation + -

seasonal effective rainfall amounts. No deep drainage or

surface runoff was considered.

Water use efficiency ðWUEÞ ¼ Grain yield ðkg ha�1ÞCrop water use ðmmÞ

The data was statistically analyzed by Statistical Analysis

Software (SAS) package (SAS Institute, 1985). Separate ana-

lyses were performed for each sampling date. Treatment

means were compared using least significant difference (LSD,

P = 0.05) procedure (Gomez and Gomez, 1984).

3. Results

During 2004–2005, a dry spell prevailed during the initial crop

growth stages until the winter rain occurred during last week

of January (Table 1). However, months of December and

January were very cold with moderate sunshine and low pan

evaporation (1–3 mm day�1) and thus plants suffered less.

During 2005–2006, though the rainfall was well-distributed

over the season, month of February was unusually warm with

no rain. However, all the plots were irrigated at 96 DAS

coinciding with this warm period to prevent further damage to

the crop.

3.1. Effect of mulching on soil water status

3.1.1. Soil moisture content at different depthsIn the first year of experiment, transparent polyethylene

recorded maximum moisture content (%, v/v) in 0–15 cm

(9.2%) and 15–30 cm (9.9%) at 67 and 85 days after pre-sowing

irrigation, closely followed by RH (8.9%) (Fig. 1). These were

significantly higher than black polyethylene (7.4%) and I0M0

Fig. 1 – Profile soil moisture content under mulch at (a) 0–15, (b) 15–30, (c) 30–45, (d) 45–60, (e) 60–75, (f) 75–90 cm depths

(2004–2005) (standard error of the mean varied between W10 and 15% of the mean value for all treatments; upper and lower

dashed lines are field capacity and wilting point of soils, respectively).

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 41326

(7.6%). During this period the crop received no water either as

irrigation or rain. Following rain, moisture content under TP

increased to 18% on 91 DAS (maximum among the mulches).

At crop maturity, maximum moisture (0–15 cm) was recorded

in I0MB (16.6%) closely followed by I1M0. Rice husk showed

moderate moisture (13%) in soil, whereas I0MT was the driest

(5%). Residual surface soil moisture at harvest was lowest

under RH. Better maintenance of soil moisture in RH was

recorded at 30–45 cm depth also. At harvest in this layer

maximum moisture was recorded under I0MB (13%), closely

followed by I0MR and I0MT (12.0 and 11.9%, respectively). In

45–60 cm depth, RH maximized the water content and

recorded 12.0 and 7.8% on 85 and 111 DAS, respectively. In

this layer, adequately irrigated plots recorded significantly

higher level of moisture after receiving irrigation and rain of

30.4 mm (84–89 DAS), but was at par with RH and BP mulched

plots subsequently. Higher soil moisture status at deeper

layers was also maintained by rice husk, during long dry

period (29–87 DAS); moisture depletion was very fast in I0M0

plots. Residual moisture was also minimum in RH at harvest.

During second year, RH retained significantly higher

moisture content (0–15 cm) and at par with TP (15–30 cm)

during initial dry periods when no irrigation was given (Fig. 2).

Most substantial moisture content in surface soil thereafter

Fig. 2 – Profile soil moisture content under mulch treatments at (a) 0–15, (b) 15–30, (c) 30–45, (d) 45–60, (e) 60–75, (f) 75–90 cm

depths (2005–2006) (standard error of the mean varied between W10 and 15% of the mean value for all treatments; upper

and lower dashed lines are field capacity and wilting point, respectively).

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 4 1327

was maintained in RH, indicating minimum depletion under

this treatment. Moisture was also more under RH following

rain (17.8 mm at 109–113 DAS) while high rate of depletion of

surface moisture was observed under no mulched plots. Rice

husk conserved marginally higher moisture in 30–45 and 45–

60 cm layers, mostly during dry periods. However, the

differences among the treatments were marginal in these

layers. Here, mulch treated plots recorded similar moisture as

unmulched adequately irrigated plots.

3.1.2. Soil moisture potentialAdequately irrigated plots showed relatively higher soil

moisture matric (tensiometric) potential over time, except at

109 DAS (8% soil moisture), while rate of decrease in potential

was more in no-mulch plots (Fig. 3). Minimum fluctuations

over time and relatively higher potential was observed under

RH on 93, 109 and 134 DAS, though not significantly different

than TP and BP mulches. The soil moisture retention

characteristic did not differ between the treatments.

3.2. Effect of mulching on soil temperature

In the first year of experiment, average soil temperature was

significantly higher under TP than RH. Diurnal variation in soil

temperature was more within 0–5 cm and reduced with depth.

Night surface soil temperature (0–10 cm) was moderate under

RH.

In the second year, average soil temperature for the entire

period (up to grain formation stage) indicated relatively cooler

environment under RH, especially at 14:30 h (Table 2). During

morning hours (10:00 a.m.), except for 7 cm depth where

adequately irrigated plots recorded significantly high soil

temperature than no mulch (limited irrigation) and TP

mulched plots, the differences in soil temperatures among

Fig. 3 – Soil moisture potential in wheat under various

mulches at (a) 0–15 and (b) 15–30 cm depths (2004–2005).

Vertical bars give LSD (5%) between treatments.th

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a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 41328

the treatments were non-significant for all the depths studied.

However, at 14:30 h, average seasonal soil temperature at 7

and 14 cm depths was significantly lower under RH than any

other treatments. At 21 and 28 cm soil depths, the noon

temperature under TP, at par with I1M0, was found to be

significantly higher than RH treatment.

3.3. Effect of mulching on plant water status

3.3.1. Relative water content of leavesRWC in leaves was maintained higher than 90% (except on 57

DAS) till 98 DAS (Fig. 4), decreased sharply and recorded 75–

80% thereafter. Rice husk maintained a better leaf water status

Ta

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Fig. 4 – Relative water content in leaves of wheat under

different mulches (2004–2005) (vertical bars represent

LSD0.05 at each sampling date).

Fig. 5 – Leaf water potential in wheat under the mulch

treatments (2004–2005) (vertical bars represent LSD0.05 at

each sampling date).

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 4 1329

for most of the time with maximum seasonal average RWC

(89.5%) closely followed by TP mulch (88.2%). Both the no-

mulch treatments (I1M0 and I0M0) showed the lowest RWC,

though the differences were statistically insignificant. Even

though RWC reduced to a maximum extent in RH following

two dry periods (83 and 111 DAS), the plants regained turgidity

quickly following rain or irrigation. After a long dry period (on

83 DAS), RWC in RH treated plots was at par with adequately

irrigated treatment, I1M0 (irrigated on 72 DAS) and signifi-

cantly higher than other two mulches. Both under BP mulch

and adequately irrigated plots, RWC increased to the max-

imum value immediately following irrigation/rain (91.6% at 97

DAS and 81.5% at 104 DAS), but could not maintain the same

subsequently (RWC reduced to 72.8% on 111 DAS).

During 2005–2006, RWC was recorded at two stages: at 72

DAS (47 days after first irrigation) and 125 DAS i.e., 24 days

after 2nd (limited) and 3rd irrigation (adequately irrigated)

(Table 3). At 70 DAS, leaf water status in RH was at par with

adequately irrigated (no mulch) treatment and was signifi-

cantly higher than TP and no mulch with limited irrigation

(I0M0) treatments. At 125 DAS, significantly higher RWC was

recorded under I1M0 and both RH and TP indicated better RWC

as compared to I0M0.

3.3.2. Leaf water potentialSimilar to soil water potential, average LWP over the season

was also higher under RH treatment (�1.72 MPa). Black and

transparent polyethylene mulch recorded the minimum

average LWP (�1.82 and �1.81 MPa, respectively) (Fig. 5). At

48 DAS, LWP was significantly lower under TP, but the

differences became insignificant afterwards. Due to long dry

period, LWP in I0M0 decreased sharply to �2.90 MPa (111 DAS)

but increased to a moderate value of�2.10 MPa, following rain

and irrigation (maximum among all the treatments). During

this time, RH showed low LWP (�2.78 MPa) while transparent

(�2.44 MPa) and BP (�2.62 MPa) showed relatively higher

values. However, over the entire growing season, more

consistent LWP values were recorded under husk compared

to other mulches.

3.3.3. Canopy temperatureDuring 2004–2005, all the treatments maintained negative

canopy air temperature difference (CATD) values for the entire

growing period and attained positive values only at harvest

(Fig. 6a). Among the mulches, it was lowest in RH and at par

Table 3 – Relative water content of leaves, dry biomass of plantreatments (2005–2006)

Treatments

Relative water content ofleaves (%)

Dry

70 DAS 125 DAS 70 D

I0M0 89.7a 86.1b –

I0MT 90.3a 88.1a –

I0MR 92.4b 88.3a –

I1M0 93.4b 90.1c –

Means within rows followed by different letters are significantly differen

with adequately irrigated plots (seasonal average value was

�3.6 8C). Fluctuations in CATD were also limited under RH

indicating minimal stress experienced by the crop. Plant

canopy was cooler under RH during second year also, even

during long dry periods (Fig. 6b). However, in contrast to

previous year, CATD in I1M0 was low. Transparent poly-

ethylene showed high CATD in both years during drier

periods, indicating stress to plants. The computed values of

CSDDs were lowest under RH, compared to other mulch

treatments.

3.4. Growth parameters

3.4.1. Specific leaf weightSLW did not vary much up to 90 DAS, thereafter declined

sharply and became constant (Fig. 7). On 72 DAS, significantly

lower SLW was recorded under BP mulch as compared to RH

and adequately irrigated (I1M0) treatment. Higher SLW was

noticed in I1M0 during the first 90 DAS as irrigation was given

to these plots on 72 DAS, while other treatments received rain

on 87–89 DAS. Lowest SLW was observed in transparent

polythene mulch, which reduced very steeply from

10.38 mg cm�2 at 64 DAS to 5.67 mg cm�2 at 76 DAS and

maintained until 90 DAS and then finally declined to

3.33 mg cm�2 by 142 DAS.

During 2005–2006, maximum SLW was recorded under

I1M0 at 70 DAS and TP showed significantly higher SLW than

ts and specific leaf weight in wheat under various

Parameters

biomass per plant (g) Specific leaf weight(mg cm�2)

AS 125 DAS 70 DAS 125 DAS

30.0a 7.81a 3.03a

28.8a 9.11b 3.11a

35.6c 8.12c 3.53b

36.3c 10.31d 4.22c

t at P = 0.05.

Fig. 6 – Thermal environment of wheat canopy under

different mulches during (a) 2004–2005 and (b) 2005–2006

(vertical bars represent LSD0.05 at each sampling date).

Fig. 8 – Accumulation of aboveground biomass in wheat

under different mulches (2004–2005) (vertical bars

represent LSD0.05 at each sampling date).

Fig. 9 – Root length density in wheat at different depth of

soil profile under various mulch treatments during (a)

2004–2005 and (b) 2005–2006.

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 41330

RH (Table 3). However, at 125 DAS, highest SLW was under

I1M0, but RH was better as compared to transparent and no

mulch treatments, the differences were statistically signifi-

cant.

3.4.2. Dry plant biomass

Dry matter accumulation (2004–2005) increased gradually (up

to 91 DAS) and then quickly reached to 30–40 g plant�1 (Fig. 8).

In TP, dry biomass reached to its peak value earlier

(26.0 g plant�1 on 127 DAS), as compared to other mulches.

In the second year, dry biomass at 125 DAS was maximum in

adequately irrigated wheat, comparable biomass was also

Fig. 7 – Specific leaf weight in wheat under various mulches

(2004–2005) (vertical bars represent LSD0.05 at each

sampling date).

obtained under RH, both were significantly higher than

transparent and no mulch under limited irrigation.

3.4.3. Root length densityRoots were mostly concentrated in 0–15 cm layer, and reduced

down the profile (Fig. 9a). Rice husk treatment produced as

much roots as adequately irrigated plots. Root length density

(0–15 cm) was significantly higher in adequately irrigated plots

than other treatments, except RH where the difference was

non-significant. In 15–30 cm depth, however, the differences

between the treatments were non-significant. In both 30–45

and 45–60 cm depths, RH and BP mulch produced root length

density similar to adequately irrigated plots, but significantly

Table 4 – Yield, water use and water use efficiency in wheat under mulches

Treatments Yield (kg ha�1) Water use (mm) Water use efficiency (kg ha�1 mm�1)

2004–2005 2005–2006 2004–2005 2005–2006 2004–2005 2005–2006

I0M0 4199a 3728a 481b 384a 8.73a 9.70a

I0MT 5019b 3870b 421a 400a 12.09b 9.65a

I0MB 4079a – 433b – 9.42c –

I0MR 5143b 4100c 402a 398a 12.79d 10.29b

I1M0 5675c 4319d 520c 461c 10.90e 9.36c

Means within columns followed by different letters differ significantly at P = 0.05.

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 4 1331

higher than TP and no mulch (limited irrigation) treatments. In

other layers (>60 cm), RH and BP produced higher RLD (the

differences were non-significant except 60–75 cm layer).

In 2005–2006, significantly higher surface (0–15 cm) RLD

were recorded in adequately irrigated plots and others were in

the following order: I1M0 > I0MR > I0MT > I0M0 (Fig. 9b).

Similar trend was observed in 15–30, 30–45, 45–60 and 60–

75 cm depths, but the difference between RH and I1M0 (30–

45 cm); RH and TP (45–60 and 60–75 cm) were non-significant.

Though roots under mulch proliferated up to 90–105 cm depth,

the difference with respect to adequately irrigated plots was

non-significant.

3.5. Yield and water use efficiency

Grain yield was maximum in adequately irrigated and

minimum in limited irrigated unmulched plots in both the

years (Table 4). Adequately irrigated wheat also recorded

significantly higher water use, lowering its water use

efficiency. Black polyethylene treated crop yielded similar to

no mulch with limited irrigation, and did not show good

promise in saving water (water use significantly lower than TP

and RH). In the second year, sudden high temperature during

3rd week of February affected the yield; however, the

reduction was less in RH (20%), as compared to transparent

polyethylene mulch (23%) and adequately irrigated plots (24%).

As unmulched plots under limited irrigation were already

under maximum stress, the reduction in yields due to the

temperature rise was to the tune of 11% only. The difference in

yield between adequately irrigated and RH plots reduced in the

second year. In terms of water use by the crop, RH saved water

to the tune of 19–22% while TP saved 13% as compared to

adequately irrigated wheat. Water use efficiency in wheat

under RH and TP was significantly higher in 2004–2005 (12.79

and 12.09 kg ha�1 mm�1) as compared to adequately irrigated

and no mulched plots (10.9 kg ha�1 mm�1), but no significant

differences were found in 2005–2006.

4. Discussion

The higher soil moisture status indicated role of mulch in

conserving the moisture in soil, though the effects between

mulches varied. Rice husk seemed to be the best in main-

taining moisture in both surface and sub-surface layers from

sowing to harvest, closely followed by TP mulch. Similar

findings under rice straw mulch were reported by Rahman

et al. (2005). The rate of drying of soil was slow, resulting in

water availability for relatively longer period during crop

growth and development. The effect was particularly pro-

nounced during dry periods, where no irrigation was given to

the crop, or no rain occurred. Conserving water at lower

depths might have been useful to crops during grain filling,

even though irrigation or rainwater was not available to the

crop (Li et al., 1999) and might have positive effect on yield of

wheat, which is in conformity with other findings (Gao et al.,

1999; Li et al., 2004; Niu et al., 2004). Less residual moisture

content in plots under RH indicated extraction of water to the

maximum possible extent by the roots, demonstrating

efficiency of RH in conserving the soil moisture for the best

use by the crop. Depletion of moisture from deeper layers was

more under no-mulched plots probably due to upward flux of

water to the drier layer above due to evaporation pull. Due to

less variation in moisture content, the soil water matric

potential under RH also showed minimum fluctuations, even

during dry spells. Change in soil moisture was most

discernible up to 75 cm depths, and was reported to change

very little beyond 120 cm depth (Zhu et al., 1990). However, in

this study soil was sampled up to 90 cm depth, which might

under estimate the water use by the crop, and subsequently

higher water use efficiency in producing grain yield (Li et al.,

1999).

It is reported that mulching with plastic films increase the

soil temperature at 0–15 cm depth, thereby reduces germina-

tion time and enhances early growth of seedlings in wheat

(Chaudhary and Chopra, 1983; Li et al., 1999). But in our study,

increase in mean soil temperature under TP mulch did not

effectively translated into increase in yield. Due to water, soil

was little warm at morning under adequately irrigated plots,

for rest of the day, differences were non-significant. Results

indicated that the increase in soil temperature could not

produce any significant effect on yield in wheat grown in a

tropical soil, where the decrease in temperature during winter

is not as low as found in temperate region, as reported

elsewhere (Rawson and Bagga, 1979; Li et al., 1999). As RH was

able to maintain an optimum temperature, even at lower

depths, the crop could produce better yield as compared to

other mulches.

Rice husk could maintain better plant water status (as

indicated by RWC and LWP), during prolonged dry periods and

recorded at par or sometime better than the adequately

irrigated treatment. Seasonal average LWP was relatively low

under RH and the rate of change was also less. Correlation

between LWP and SWP was also better under the rice husk.

When soil water and LWP data pertaining to various

treatments during particular day of observation were pooled,

Fig. 10 – Relation between soil and leaf water potential in

wheat (pooled data across the treatments).

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 41332

logarithmic relationship with good agreement (R2 = 0.71) was

obtained (Fig. 10).

Seasonal average CATD was more with TP (�2.7 8C) as

against RH (�3.6 8C); sudden peaks of CATD during dry periods

under TP indicated stress in plants under this treatment. For

most of the observation days, the differences among the

treatments were significant, indicating CATD as a useful and

reliable indicator in monitoring water status in plants. The

computed values of cumulative CATD were also lower under

RH. Canopy air temperature difference on a particular day was

positively related to the biophysical parameters, but overall no

significant correlation was obtained, except for grain yield and

CSDDs calculated over the entire growth period (linear with

R2 = 0.58). Reduction in grain yield to the tune of 26.6 kg ha�1

was expected with 1 8C increase in SDD (Fig. 11). Good

correlation between canopy temperature depression and yield

in wheat was also reported elsewhere (Reynolds et al., 2001).

Maximum SLW and biomass were recorded in adequately

irrigated wheat as the crop received maximum water, which

might trigger more photosynthesis. Among the mulches, RH

showed significantly higher SLW indicating relatively healthy

biomass under this treatment. Rice husk and BP also gained

similar biomass, though the latter could not effectively

translate this to yield (Table 4). Improved dry matter and

grain yield with limited water supply under RH demonstrates

the efficiency of this mulch in utilizing the conserved soil

moisture to favour more growth and yield. Improved crop

Fig. 11 – Grain yield of wheat as influenced by cumulative

stress degree days (pooled data for all mulches and both

the years).

establishment and dry biomass under straw mulch, due to

reduced water stress during dry periods was also reported by

Badaruddin et al. (1999).

Even though maximum root length density (0–15 cm) was

observed in adequately irrigated wheat, among mulches, roots

were significantly higher under RH in most of the soil depths.

Alleviated mechanical resistance through conservation of

moisture improved the root growth under these treatments

which is in conformity with other findings (Sharma and

Acharya, 2000; Rahman et al., 2005). Higher RLD under RH was

also reported by Rahman et al. (2005). Higher root development

could enhance water and nutrient absorption capacity,

thereby increasing the grain yield (Boatwright et al., 1976;

Cumbus and Nye, 1985; Li et al., 1999). Deeper rooting before

grain filling (root samples were taken at the peak vegetative

stage) might have triggered better crop biomass and subse-

quently more grain yield (Liu and Li, 2005). Positive relation-

ships were found between grain yield and root length density

and water use with moderate correlation (data not presented).

Increase in yield is associated with improved root length

density, more so in 0–30 cm depth, whereas rate of increase in

yield is likely to slow down with water use after a certain limit.

However, in the present study, optimum root length density

and water use was recorded as 0.85–0.90 cm3 cm�3 and 450–

500 mm corresponding to yield of 5.0 Mg ha�1 in wheat.

Significantly higher yields were recorded in adequately

irrigated wheat with significantly higher water use, thereby

lowering thewater use efficiency. More WUE under the mulches

compared to no-mulch demonstrates the effectiveness of

mulch in reducing soil evaporation and increased plant

respiration (Zhang et al., 1999; Zhao et al., 1996). Among the

mulches, RH showed higher yields, lower water use and thereby

recording the highest water use efficiency. Increase in biomass

and grain yield in the mulched plots were also reported by

others (De et al., 1983; Niu et al., 1998, 2004; Wang et al., 2004).

Results indicate that higher crop yields in the semi-arid region

may be achieved by using irrigation or a proper combination of

RH and irrigation, as also suggested by Huang et al. (2005). Yield

under BP mulch was similar to no mulch with limited irrigation,

and the water use being higher, recorded significantly lower

water use efficiency than TP and RH. Yields were reduced in

2005–2006, due to sudden high temperature during 3rd week of

February, but the reduction was less in RH as compared to other

treatments including the adequately irrigated wheat. As

increase in WUE improves the grain yield, use of RH proved

to be effective in improving the yield in the present experiment

with saving of water. However in the present study, rainfall

during vegetative stage was similarly low in both the years, and

the second year crop suffered because of sudden increase in

temperature during grain filling stage affecting adversely the

grain yield, and therefore, the effect of mulching on yield

response could not be clearly pronounced as reported in the

study of Sandhu et al. (1992).

5. Conclusion

Compared to polyethylene mulch, RH was found to provide a

better soil physical environment in terms of soil moisture

retention, especially during long dry periods when the crop

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 1 3 2 3 – 1 3 3 4 1333

was exposed to water stress, and optimal soil temperature

during the crop growth. These favourable conditions led to

maintenance of cooler canopy and higher plant water status.

Crop growth in terms of SLW and root length density, though

considerably higher in adequately irrigated wheat, RH

performed satisfactorily with less water use, enhancing the

water use efficiency in crop. Overall, rice husk in comparison

to polyethylene mulches, showed to have a good potential for

saving water with comparable growth and yield in wheat

under the sub-tropical soil and climatic conditions as in the

present study.

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