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: [email protected], [email protected]
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
em
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6.2
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a(1
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a(1
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a(1
1.6
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)13.1
a(1
1.3
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a(1
1.4
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0.5
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ab
(10.0
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a(1
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a(1
0.5
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bc
(12.3
–16.7
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a(1
1.2
–16.0
)13.8
b(1
1.6
–16.0
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)11.9
b(8
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b(1
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ac
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a(1
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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
ble
2–
Av
era
ge
soil
tem
pera
ture
(8C
)u
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er
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7
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0h
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012.1
a(1
0.2
–16.5
)16.2
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(14–1
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T12.2
ab
(10.3
–16.9
)16.8
b(1
4.7
–2
I0M
R12.3
bc
(9.5
–15.6
)15.9
c(1
3.3
–2
I1M
012.5
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–1
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ns
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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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