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Field Crops Research 121 (2011) 209–225

Contents lists available at ScienceDirect

Field Crops Research

journa l homepage: www.e lsev ier .com/ locate / fc r

rowth, yield and water productivity of zero till wheat as affected by rice strawulch and irrigation schedule

alwinder-Singha, E. Humphreysb,∗, P.L. Eberbacha, A. Katupitiyac, Yadvinder-Singhd, S.S. Kukald

Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, AustraliaInternational Rice Research Institute (IRRI), DAPO 7777, Metro Manila, PhilippinesMurray-Darling Basin Authority, GPO Box 1801 Canberra, ACT 2601, AustraliaPunjab Agricultural University, Ludhiana, 141004 India

r t i c l e i n f o

rticle history:eceived 12 August 2010eceived in revised form 1 December 2010ccepted 2 December 2010

eywords:orth-west Indiaater use

oil temperatureumulative pan evaporation

a b s t r a c t

Intensive cultivation of rice and wheat in north-west India has resulted in air pollution from rice strawburning, soil degradation and declining groundwater resources. The retention of rice residues as a surfacemulch could be beneficial for moisture conservation and yield, and for hence water productivity, inaddition to reducing air pollution and loss of soil organic matter. Two field experiments were conductedin Punjab, India, to study the effects of rice straw mulch and irrigation scheduling on wheat growth, yield,water use and water productivity during 2006–2008. Mulching increased soil water content and this ledto significant improvement in crop growth and yield determining attributes where water was limiting,but this only resulted in significant grain yield increase in two instances. There was no effect of irrigationtreatment in the first year because of well-distributed rains. In the second year, yield decreased withdecrease and delay in the number of irrigations between crown root initiation and grain filling. Withsoil matric potential (SMP)-based irrigation scheduling, the irrigation amount was reduced by 75 mmeach year with mulch in comparison with no mulch, while maintaining grain yield. Total crop water use(ET) was not significantly affected by mulch in either year, but was significantly affected by irrigationtreatment in the second year. Mulch had a positive or neutral effect on grain water productivity withrespect to ET (WPET) and irrigation (WPI). Maximum WPI occurred in the treatment which received

the least irrigation, but this was also the lowest yielding treatment. The current irrigation schedulingguidelines based on cumulative pan evaporation (CPE) resulted in sub-optimal irrigation (loss of yield) inone of the two years, and higher irrigation input and lower WPI of the mulched treatment in comparisonwith SMP-based irrigation scheduling. The results from this and other studies suggest that farmers inPunjab greatly over-irrigate wheat. Further field and modelling studies are needed to extrapolate thefindings to a wider range of seasonal and site conditions, and to develop simple tools and guidelines toassist farmers to better schedule irrigation to wheat.

. Introduction

Rice–wheat (RW) systems provide 85% of the total cereal pro-uction and 52% of the total calorie intake in India (FAO, 2007). The

tates of Punjab, Haryana, Uttar Pradesh, Bihar and West Bengal arehe heartland of RW systems (Yadav, 1998). In recent years, the sus-ainability of RW systems has come into question, faced with yieldtagnation or decline of rice and/or wheat yields (Ladha et al., 2003),

∗ Corresponding author. Tel.: +63 2 580 5600–9x2342; fax: +63 2 580 5699.E-mail addresses: balwinderpau@gmail.com, bsingh@csu.edu.au ( Balwinder-

ingh), e.humphreys@cgiar.org (E. Humphreys), peberbach@csu.edu.au (P.L. Eber-ach), asitha.katupitiya@mdba.gov.au (A. Katupitiya), yadvinder16@rediffmail.comYadvinder-Singh), sskukal@rediffmail.com, sskukal1@gmail.com (S.S. Kukal).

378-4290/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.fcr.2010.12.005

© 2010 Elsevier B.V. All rights reserved.

soil degradation (Bhandari et al., 2002), declining ground watertables (Hira et al., 2004), and air pollution (Bijay-Singh et al., 2008).More than 90% of the main RW areas in north-west India (Punjab,Haryana, western Uttar Pradesh) is irrigated using groundwater,and the rapid decline in groundwater levels is probably the biggestchallenge to the sustainability of the RW system (Humphreys et al.,2010).

The RW system of north-west India is highly mechanised incomparison with other RW regions. After combine harvesting ofrice, the residues are normally burnt prior to establishing wheat

(Gajri et al., 2002). Approximately 16 Mt of rice straw are cur-rently burnt each year in Punjab alone (Yadvinder-Singh et al.,2008). Farmers burn the residues because many tillage passes arerequired for incorporation, coupled with the need to allow time forthe straw to decompose sufficiently to avoid N immobilisation at

210 Balwinder-Singh et al. / Field Crops Research 121 (2011) 209–225

Table 1Soil physical and chemical properties of the experimental site.

Depth (cm) Bulk density (g cm−3) Soil texture pH Organic C (g C kg−1)

Sand (%) Silt (%) Clay (%)

0–15 1.50 46.0 21.3 32.7 8.1 0.3715–30 1.71 24.0 34.7 41.2 8.3 0.2230–60 1.46 15.4 39.4 45.1 7.9

21

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60–90 1.48 40.090–120 1.33 66.6

120–150 1.39 89.5150–180 1.42 89.5

he time of sowing. Thus, incorporation of rice straw delays wheatowing beyond the optimum date for maximum yield. Over theast decade, wheat establishment using the Pantnagar zero till drillas became popular among farmers (Harrington and Hobbs, 2009),liminating tillage and enabling earlier sowing. However, use ofhis seed drill also requires removal (normally by burning) of ateast the loose residues left by the combine harvester. Burning ofice residues is a major source of air pollution in the region, in theorms of greenhouse gas emissions (CO2, CH4, NO2, N2O) and par-iculate matter (Gupta et al., 2004). Grace et al. (2003) reported anncrease in respiratory and eye problems due to rice stubble burn-ng; other negative impacts on society include loss of biodiversitynd structures, disruption of road and air traffic, and adverse effectsn animal health and productivity (Yadvinder-Singh et al., 2008;ingh et al., 2008). Burning crop residues also destroys organic mat-er and results in large nutrient losses. All of the C, 90% of the N, 60%f the S, and 20–25% of the P and K in the rice straw are lost throughurning (Dobermann and Fairhurst, 2002). Yadvinder-Singh et al.2008) estimated the loss through burning in Punjab at around5 kg N ha−1, 21 kg K ha−1 and 3 kg ha−1 each of P and S. Thus tech-ologies that enable retention of rice residues would greatly reduceir pollution and improve soil fertility.

The recent development of a residue/trash handling zero tillageowing implement, the ‘Happy Seeder’ (Sidhu et al., 2007, 2008)rovides the capability of direct drilling wheat in rice residues.he technology is now recommended to the farmers in Punjab,nd is in the early stages of adoption. The Happy Seeder simul-aneously cuts and removes the straw in front of the sowing tynes,nd spreads the straw on the surface as mulch behind the tynes.etaining the residues as a mulch also offers the potential benefitsf reduced water loss due to the suppression of soil evaporationEs), reduced runoff, suppression of weeds, increased soil organic, and improved soil structure (Yadvinder-Singh et al., 2005).

Higher soil water content and increased yield of wheat withice straw mulch have previously been reported from India andangladesh (Sidhu et al., 2007; Rahman et al., 2005). It is wellstablished that mulch can suppress Es (Al-Darby et al., 1989; Jalotand Prihar, 1990; Jalota, 1993) and Es can account for 30–60% ofotal evapotranspiration (ET) during wheat production (Siddiquet al., 1990). This suggests that reducing Es may reduce ET and thusesult in increased water productivity based on ET (WPET) by about0–20% (Deng et al., 2006). Thus mulching could be beneficial inerms of reducing water loss from the groundwater, as well asn reducing irrigation requirement (Mandal and Ghosh, 1984; Lit al., 2004).

Zero till sowing has already been shown to reduce the amountf irrigation water needed for wheat in north-west India (Erensteinnd Laxmi, 2008; Erenstein et al., 2008). Rainfall in the same regionuring the wheat growing season (average 120 mm but highly

ariable) does not meet the crop water use (ET) needs of a highielding crop (∼320 mm, Jalota and Arora, 2002); typically 4–6 irri-ations are applied. Current irrigation scheduling guidelines forheat in north-west India are based on growth stage or cumulativean evaporation (CPE), and do not take into account the real-time

1.5 38.6 7.87.1 15.8 7.86.2 4.3 –6.5 4.2 –

availability of water in the soil profile (Prihar et al., 1974, 1976).Irrigation scheduling based on soil matric potential (SMP) (Kukalet al., 2005) integrates the effects of soil type, mulch, weather andcrop growth stage on water availability, and has been successfullyused for irrigation scheduling for rice, but has not been devel-oped for wheat. To take advantage of the potential water savings ofmulching, irrigation scheduling guidelines which take into accountthe availability of soil water are needed. Therefore we undertook astudy to evaluate the effects of mulching and irrigation schedulingon wheat crop performance, components of the water balance andwater productivity.

2. Materials and methods

2.1. Experimental site

A replicated field experiment to investigate the effects ofmulching and irrigation management on growth, yield and waterproductivity of zero till wheat was conducted for two seasons(2006–2007 and 2007–2008) at the Punjab Agricultural Uni-versity (PAU) farm at Ludhiana (30◦56′N, 75◦52′E, 247 m ASL),Punjab, India. The region is characterized by a sub-tropical andsemi-arid climate with a hot dry summer (March–June), wet mon-soon season (late June–mid September) and a cool, dry winter(October–February). Average annual rainfall is 734 mm (consti-tuting 44% of pan evaporation) of which about 80% is receivedduring the monsoon. The topsoil of the experimental site was clayloam overlying silty clay, with an abrupt change to sandy loam atabout 90 cm (Table 1). Bulk density was 1.50 g cm−3 in the top-soil, and there was a hard pan (1.71 g cm−3) at 15–30 cm. The soilwas slightly alkaline (pH 7.8–8.3) with low soil organic C contentwhich decreased from (3.7 g C kg−1 at 0–15 cm to 2.2 g C kg−1 at15–30 cm). The experimental site had been under a RW system formore than 5 years.

2.2. Experimental design

The experiment was laid out in a randomized block split plotdesign with 2 mulching treatments (with and without rice straw)as the main plots and 6 irrigation treatments (see below) in sub-plots. The irrigation treatments included recommended practice(based on CPE), and a range of water deficit treatments where irri-gation was withheld at different stages, or where the CPE intervalbetween irrigations was increased. The water deficit treatmentswere included to test the hypothesis that mulching conserves soilwater and reduces the irrigation requirement for maximum yield.There was also one irrigation treatment based on SMP, as this islikely to better reflect crop needs than scheduling based on CPE.There were 4 replicates and sub-plot size was 12 m × 6 m. The six

irrigation treatments were:

I1—irrigation when SMP decreased to −40 kPa at 15–20 cm soildepth for the first irrigation, and at 40 cm for subsequent irriga-tions;

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I2 (control)—irrigation around the time of crown root initiation(CRI, 36 d after sowing (DAS) in 2006, 27 DAS in 2007) and there-after when the ratio of the amount of irrigation water (IW) appliedat the previous irrigation to CPE minus rain decreased to 0.9, i.e.IW/(CPE − rain) = 0.9 (recommended practice) (Prihar et al., 1974);I3—same as I2 minus the irrigation at CRI;I4—one irrigation at CRI then irrigation when IW/(CPE − rain) = 0.6;I5—one irrigation only, at CRI;I6—as for I2 minus the last irrigation.

A depth of 75 mm was applied at each irrigation of all treat-ents, therefore IW/(CPE − rain) ratios of 0.9 and 0.6 are equivalent

o CPE of 83 and 125 mm, respectively, between irrigations, in thebsence of rain. Soil matric potential in I1 was measured usingube tensiometers and a SoilSpec® vacuum gauge. The tensiome-ers were installed mid-way between the plant rows with the tips at5–20 and 35–40 cm. Soil tension-based irrigation scheduling wassed to try and avoid yield-limiting water deficit stress. Soil ten-ion at the shallower depth was used to schedule the first irrigationefore the roots had proliferated to depth, and the 35–40 cm depthas chosen for subsequent irrigations as the majority of the roots inell-irrigated wheat at the time of heading are located at 0–40 cm

n the soils of Punjab (Yadvinder-Singh et al., 2009). A threshold of40 kPa was considered to be high enough to avoid yield-limitingater deficit stress, although there is a paucity of data on the opti-um threshold for wheat and other cereal crops. With SMP-based

rrigation scheduling, the mulched and non-mulched treatmentsere usually irrigated on different days because of the effect ofulch on soil water content. For irrigation schedules based on CPE,

oth mulched and non-mulched treatments were always irrigatedn the same day. Each plot was irrigated separately via a piped irri-ation system using ground water (0.6 dS m−1). Irrigation volumeas measured with a Woltman® helical turbine meter.

.3. Crop management

The preceding rice crop was harvested by combine in mid Octo-er each year, leaving standing straw (20–25 cm) and loose residuestotal residues 8–9 t ha−1 with a C:N ratio 75:1). In the non-mulchedreatment the rice straw was removed mechanically, without dis-urbing the soil surface, leaving stubbles about 3–5 cm high. Theoose residues in the plots to be mulched were manually distributedniformly across each plot prior to sowing. Wheat (var. PBW343)as sown into residual soil moisture using a Combo Happy Seeder

Sidhu et al., 2007, 2008) on 6th November 2006 and 13th Novem-er 2007. The machine was configured to cut the stubbles in frontf the sowing tynes (cutting a 7.5 cm wide strip), with a strip oftanding stubbles (12.5 cm wide) between the sowing rows. Rec-mmended practices were used for sowing, fertilizer and pestanagement. A seed rate of 100 kg ha−1 was used at a sowing depth

f 3–5 cm and row spacing was 20 cm. Diammonium phosphate23 kg N ha−1 and 26 kg P ha−1) was applied with the seed. Urea wasroadcast at 37 kg N ha−1 prior to sowing, and a further 60 kg N ha−1

s urea was broadcast just prior to the time of the irrigation atRI. Weeds were controlled by spraying Leader® (sulfosulfuron) at2.5 g a.i. ha−1 and 2,4-dichlorophenoxyacetic acid at 625 g a.i. ha−1

ithin 1 week after the first irrigation.

.4. Soil water dynamics

Gravimetric soil water content was determined on samples col-

ected by auguring to a depth of 180 cm in all plots at sowing andarvest. Soil samples were collected at depth intervals of 15 cm forhe top two layers, and at intervals of 30 cm from 30 to 180 cm.he volumetric water content (VWC) was determined from gravi-etric water content and bulk density using a particle density of

esearch 121 (2011) 209–225 211

2.65 g cm−3. Soil bulk density was determined by taking undis-turbed soil cores from the sides of an open pit in the middle of thefield. Soil cores were taken with 5.5 cm ID × 5 cm high steel cylin-drical rings, centred at depths of 7.5, 22.5, 45, 75, 105, 135 and165 cm. Soil water depletion between sowing and harvest was cal-culated from the difference in VWC of the 0–180 cm profile at thesetimes.

Soil matric potential was determined at depths of 20, 40, 60,80, 100, 120, 140, 160, 180 cm in 4 replicates of treatments I1and I2. The tensiometers were installed 1 week after sowing in2006–2007, and 4 d after sowing in 2007–2008, between the croprows and about 50 cm apart from each other. The tensiometers wereinstalled in tight fitting holes sealed with a bentonite plug at thetop, and were usually read twice a week and immediately beforeirrigation.

2.5. Evapotranspiration

Evapotranspiration (ET, mm) was estimated using a standardwater balance equation: ET = dSWC + P + I − D − R, where dSWC isthe change in soil water content (0–180 cm) between sowing andharvesting, P is precipitation, I is the amount of irrigation, D is thedrainage beyond 180 cm and R is runoff. Drainage was assumed tobe negligible as tensiometers installed at 120, 140, 160 and 180 cmsuggested no water movement beyond 120 cm as there was nochange in SMP at any of these depths following irrigation or rain.There was no runoff from the plots as they had small bunds.

2.6. Soil temperature

Soil temperature was measured during the 2007–2008 crop sea-son using mercury-in-glass thermometers installed at 5 depth in I2in three replicates, at 9.00 am (“minimum”) and 2.30 pm (“maxi-mum”).

2.7. Plant density, growth and yield

Plant density was measured in five 1 m long rows at two loca-tions in each plot after complete emergence, just before the firstirrigation. In the mulched treatments, plant density is presentedas the mean of the number of plants that had emerged throughthe mulch. The uniformity of establishment was determined asthe coefficient of variation (CV) of the plant number in individ-ual rows. Tiller and spike counts were done at two fixed locations(5 rows × 1 m) in each plot every 2 weeks throughout the season.At the same times, biomass samples were taken from 3 rows × 1 min each plot, sun dried and then oven dried to determine total dryweight. At maturity, grain and straw yields were determined onan area of 15 m2 in the middle of each plot by manually harvest-ing and mechanically threshing the samples. Total air-dried weightof grain and straw was measured in the field using a digital springbalance, and grain and straw moisture content were determined bydrying sub samples at 70 ◦C, for calculation of dry grain and strawyields. The number of grains per spike was determined on 20 spikesrandomly selected from each plot. Average grain weight (dry) wasdetermined on 1000 grains randomly sampled from the large areaharvest.

2.8. Water productivity

Water productivities with respect to ET (WPET), irrigation (WPI)

and total water input (irrigation + rain) (WPI+R) were calculated forgrain and total above ground biomass at harvest as follows:

Grain WPET (kg ha−1 mm−1) = Grain yield (kg ha−1)Total seasonal ET (mm)

2 Crops Research 121 (2011) 209–225

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12 Balwinder-Singh et al. / Field

iomass WPET (kg ha−1mm−1) = Total biomass (kg ha−1)Total seasonal ET (mm)

rain WPI(kg ha−1 mm−1) = Grain yield (kg ha−1)Total irrigation amount (mm)

iomass WPI(kg ha−1 mm−1) = Total biomass (kg ha−1)Total irrigation amount (mm)

rain WPI+R (kg ha−1 mm−1) = Grain yield (kg ha−1)Total irrigation + rainfall (mm)

iomass WPI+R(kg ha−1 mm−1) = Total biomass (kg ha−1)Total irrigation + rainfall (mm)

.9. Weather data

Rainfall was measured daily using a manual rain gauge installedt the site. Other meteorological data were collected from theeather station on the PAU farm, located about 1.5 km from the

xperimental site. Data collected included daily maximum andinimum temperatures, pan evaporation and sunshine hours.

.10. Statistical analysis

Statistical analysis of the data was done using Genstat version0.0 with a factorial RBD design. Treatment means were comparedn the basis of least significant difference at the 95% and 90% con-dence level.

. Results

.1. Weather

Total rainfall during the 2006–2007 wheat season was 159 mmnd was well distributed (Fig. 1a), so only one post-sowing irri-ation was applied to the control treatment (I2). The 2007–2008eason was generally dry, with total growing season rainfall of8 mm, half of which was received late in the season (towards thend of grain filling), and three post sowing irrigations were appliedo the control. Total pan evaporation (November-April) was sim-lar to the long term average (597 mm) in 2007–2008 (578 mm)nd lower in 2006–2007 (531 mm). Monthly mean daily sunshineours were similar to the long term values in both years, except in

anuary 2008 when sunshine hours were relatively low, while theyere relatively high in February 2008 (Fig. 1b). In February 2007,ean daily minimum temperature was very high compared with

008 and the long term average (Fig. 1c). In January 2008, meanaily maximum temperature was relatively low due to some frostyays in mid-late January, and both maximum and minimum tem-erature were relatively high in March 2008. During the grain fillingeriod the average maximum temperature was 31 ◦C in 2007–2008nd 29.0 ◦C in 2006–2007, and average minimum temperature was5.5 and 13.0 ◦C, respectively.

.2. Field experiment 2006–2007

.2.1. Irrigation treatments

The first post-sowing irrigation was applied to all treatments

6 d after sowing (DAS), about 10 d later than CRI due to rain-all (14 mm) at 14 DAS. There was no further irrigation to any ofhe treatments due to the well-distributed rainfall, except for onerrigation at 76 DAS to the non-mulched treatment with irrigation

Fig. 1. (a) Monthly total pan evaporation and rainfall (mm), (b) monthly meandaily sunshine hours, (c) monthly mean maximum and minimum temperature dur-ing the 2006–2007 and 2007–2008 wheat seasons in comparison to the long term(1971–2006) data.

scheduling by tensiometer (I1). Therefore, there were only two irri-gation treatments—I1 and I2. Treatments I3, I4, I5 and I6 were thesame as treatment I2.

3.2.2. Soil matric potentialA week after sowing, the soil in the non-mulched treatment was

significantly drier than in the mulched treatment, to a depth of40 cm, the difference being highest in the top layer (Fig. 2). Afterthe first irrigation at 36 DAS, the degree of drying was again greater

in the non-mulched than mulched treatment to a depth of 40 cm.The rate of soil drying decreased with depth, and by about 90 DAS(after maximum tillering) the soil at 10 and 20 cm had dried beyondthe measurement range of the tensiometers (∼−70 kPa) in bothmulching treatments of I2. After the last rain in late-February, all

Balwinder-Singh et al. / Field Crops Research 121 (2011) 209–225 213

10cm

X Data

Mat

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(mm

)

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MulchNon-mulchRain/Irrigation

20cm

Mat

ric

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l (kP

a)

-90

-70

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40cm

Mat

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160140120100806040200

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ig. 2. Effect of mulch on soil matric potential in irrigation treatment I2 at 10, 20, 40f the means). There are missing data at 10 and 20 cm between 85 and 95 DAS whe

oil layers to a depth of 40 cm again dried faster in the non-mulchedheat compared to the mulched wheat. Soil matric potential was

elatively constant at 60 cm during the first half of the season,ut increased towards maturity and with a consistent tendency toemain higher in the non-mulched treatment, but there were fewignificant differences between mulching treatments at this depth.here was no change in SMP at depths beyond 120 cm during wholerop season.

.2.3. Crop development, establishment and growthThe crop emerged through the soil about 7 DAS in the non-

ulched treatments, and through the mulch about 9 DAS (Table 2).

ifty per cent anthesis occurred 105 DAS and 111 DAS in non-ulched and mulched wheat, respectively. Physiological maturityas also delayed with mulch by about 10 d, from 153 to 163 DAS.

There were no significant (p < 0.05) interactions between irri-ation and mulching treatments for any of the measured crop

sowing

60 cm depth during the 2006–2007 wheat season (vertical bars are standard errorssoil was drier than the range of measurement of the tensiometers (−70 kPa).

parameters at any stage, and no significant effects of irrigationtreatment, but the effect of mulching was often significant. Forsimplicity, and for comparison with the results of the control (I2)in 2007–2008, only the results for I2, with and without mulching,are presented for the patterns of tiller development and biomassaccumulation. Plant density was significantly higher without mulch(130 plants m−2) than with mulch (109 plants m−2). During earlyto mid tillering, tiller density was slightly but significantly higherwithout mulch than with mulch, probably due to the higher plantdensity without mulch, but by maximum tillering (75 DAS) bothresidue treatments had similar tiller density (∼525 tillers m−2)(Fig. 3a). However, between maximum tillering and 105 DAS, the

rate of tiller mortality in I2 was higher in the non-mulched treat-ment (40%) than in the mulched treatment (28%). As a result, at105 DAS, tiller density was significantly lower in the non-mulchedtreatment, and remained significantly lower for the rest of the sea-son.

214 Balwinder-Singh et al. / Field Crops Research 121 (2011) 209–225

Table 2Crop phenology as affected by residue treatment.

Growth stage Mulch treatment 2006–2007 2007–2008

Sowing date 6 November 13 November

Emergence Non mulch 13 November (7)a 20 November (7)Mulch 15 November (9) 22 November (9)

Flowering Non mulch 19 February (105) 3 March (113)Mulch 25 February (111) 12 March (122)

itbittb6(o

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Fam

combinations was similar (mean 353 mm) (Table 4). The sources

Physiological maturity Non mulchMulch

a Figures in parentheses are days after sowing.

As for tiller production, the rate of biomass accumulation wasnitially higher without mulch (46 kg ha−1 d−1 from establishmento mid-tillering) than with mulch (34 kg ha−1 d−1) (Fig. 3b). Theiomass accumulation rate in I2 was higher under mulch dur-

ng the period prior to anthesis (85–110 DAS) when biomass inhe mulched treatments increased at 115 kg ha−1 d−1 comparedo 65 kg ha−1 d−1 without mulch. From anthesis to maturity, theiomass accumulation rate was 72 kg ha−1 d−1 with mulch and4 kg ha−1 d−1 without mulch. The net result was significantlyp < 0.05) higher total biomass (10.6 t ha−1) with mulch than with-ut mulch (9.2 t ha−1).

.2.4. Yield and yield componentsThere was no significant (p < 0.05) effect of irrigation treatment,

or interaction between irrigation and mulching treatments, onield and all yield components. Mulch increased grain yield due toignificantly higher spike density and grain weight (Table 3). How-ver, the interaction was significant at p < 0.10 for grain yield, spike

0

100

200

300

400

500

600

180160140120100806040200

Till

er d

ensi

ty (

m2 )

Days after sowing

a

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Non-mulch

0

2

4

6

8

10

12

180160140120100806040200

Bio

mas

s (t

ha-1

)

Days after sowing

b

Mulch

Non-mulch

ig. 3. (a) Tiller density and (b) biomass production in irrigation treatment I2 withnd without mulch during 2006–2007 (vertical bars are LSD (p = 0.05) for comparingulching treatments).

8 April (153) 10 April (149)18 April (163) 16 April (155)

density and grain weight. At p < 0.10 mulch increased grain yield ofI2 (from 4.0 to 4.5 t ha−1) due to significantly higher spike densityand grain weight, while yields of I1 with and without mulch weresimilar. Neither the number of grains spike−1 nor harvest indexwere influenced by mulching.

3.2.5. Water use and water productivityWith SMP-based irrigation scheduling (I1), the non-mulched

treatment received 2 irrigations (150 mm) compared with one irri-gation (75 mm) with mulching (Table 4). Both the mulched and thenon-mulched treatments of I2 received one irrigation, at the sametime as the first irrigation of I1.

Total crop water use (ET) in all irrigation × mulching treatment

of water were rainfall (159 mm), residual soil water from the pre-ceding rice crop (87–126 mm) and irrigation. At the time of sowingthe water content of the upper soil profile was close to field capac-ity, except in the topsoil (Fig. 4a). By harvest time, the soil profile

Fig. 4. Volumetric soil water content in irrigation treatment I2 at sowing and atharvest during (a) 2006–2007 and (b) 2007–2008 (vertical bars are standard errorsof the means).

Balwinder-Singh

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Table 3Yield and yield components under mulch and irrigation treatments in 2006–2007 and 2007–2008.

Grain yield (kg ha−1) Spike density (no. m−2) Grains per spike Grain weight (mg) Harvest indexMulch Non mulch Mean Mulch Non mulch Mean Mulch Non mulch Mean Mulch Non mulch Mean Mulch Non mulch Mean

2006–2007I1 4230 3890 4060 340 312 326 37.2 39.2 38.2 42.9 43.5 43.2 0.40 0.42 0.41I2 4510 3990 4250 374 325 350 38.5 40.5 39.5 43.2 39.7 41.5 0.43 0.43 0.43Mean 4370 3940 357 319 37.9 39.9 43.1 41.6 0.42 0.43LSD (0.05)Residue 242 21 NS 0.8 NSIrrigation NS NS NS NS NSInteraction NS NS NS NS NSLSD (0.10)Residue 247 34 NS 0.2 NSIrrigation 247 34 NS 0.2 NSInteraction 350 48 NS 2.0 NS2007–2008I1 3840 3620 3730 392 381 386 35.2 38.6 36.9 41.0 39.2 40.1 0.37 0.38 0.37I2 4090 3980 4040 393 373 383 35.6 38.2 36.9 41.1 37.9 39.5 0.40 0.39 0.40I3 4340 4220 4280 311 294 303 38.5 41.9 40.2 41.6 37.6 39.6 0.40 0.43 0.41I4 3580 3590 3590 380 361 370 35.7 37.4 36.6 39.1 38.2 38.7 0.42 0.41 0.41I5 3270 3130 3200 368 338 353 31.6 32.1 31.8 36.7 35.4 36.0 0.38 0.38 0.38I6 3920 3520 3720 384 359 371 35.9 36.3 36.1 35.9 36.6 36.2 0.38 0.42 0.40Mean 3840 3678 371 351 35.4 37.4 39.5 37.5 0.39 0.40LSD (0.05)Residue NS 17 1.1 0.7 NSIrrigation 310 16 2.0 1.3 NSInteraction NS NS NS NS NSLSD (0.10)Residue 150 8 1.1 0.7 NSIrrigation 260 13 1.9 1.1 NSInteraction 370 18 2.6 2.3 NS

216 Balwinder-Singh et al. / Field Crops Research 121 (2011) 209–225

Table 4Components of the water balance as affected by mulch and irrigation treatments in 2006–2007 and 2007–2008.

Irrigation treatments Irrigation (mm) Rainfall (mm) dSWCa (mm) Water use (ET) (mm)

Mulch Non mulch Mulch Non mulch Mulch Non mulch Mean

2006–2007I1 75 150 159 126 87 360 367 364I2 75 75 159 107 111 341 345 343LSD (0.05)Residue – – NS NSIrrigation – – NS NSInteraction – – 28 NS

2007–2008I1 150 225 88 125 71 363 384 374I2 225 225 88 87 91 400 404 402I3 150 150 88 135 116 369 350 360I4 150 150 88 128 120 362 354 358I5 75 75 88 143 127 306 290 298I6 150 150 88 123 119 357 353 355LSD (0.05)Mulch – – 10 NS

cm p

haddwtd

haaaaWt(bsbsgi

3

3

fio((0bm(nt

3

mdt

Irrigation – –Interaction – –

a dSWC is the decrease in soil water content between sowing and harvest (0–180

ad dried to a depth of about 90 cm. There was a significant inter-ction between mulching and irrigation treatments on soil waterepletion between sowing and harvest, with significantly higherepletion in I1 with mulching than without mulching, consistentith the fact that the non-mulched treatment received an addi-

ional irrigation. There was no effect of mulching on soil waterepletion in I2.

Grain and total biomass WPET were slightly but significantlyigher with mulch than without mulch in both I1 and I2 (Fig. 5and b), as a result of trends for higher grain and biomass yieldnd slightly lower ET with mulch. There was a significant inter-ction between mulching and irrigation treatments on both WPI

nd WPI+R of grain and total biomass. Both grain and biomassPI and WPI+R with mulching were significantly (p < 0.05) higher

han without mulching with SMP-based irrigation scheduling (I1)Fig. 5c–f). Grain WPI+R was not affected by mulching with CPE-ased irrigation scheduling (I2), but biomass WPI+R was slightly butignificantly higher with mulch. In the absence of mulch, grain andiomass WPI and WPI+R were significantly higher with CPE-basedcheduling than SMP-based scheduling because the additional irri-ation to non-mulched I1 did not result in proportional increasesn grain or biomass yield.

.3. Field experiment 2007–2008

.3.1. Irrigation treatmentsWith SMP-based irrigation scheduling (I1), mulch delayed the

rst irrigation by 7 d and the second by 29 d, and averted the needf a third irrigation in contrast with the non-mulched treatmentTable 5). Irrigation scheduling using the recommended practiceI2: IW/(CPE − rain) = 0.9) resulted in 3 irrigations, while a ratio of.6 (I4) resulted in 2 irrigations. I3 and I6 also received 2 irrigations,ut the first irrigation of I3 did not occur until 100 DAS, while I6issed out on the last irrigation in comparison with the control

I2). Treatment I5 received only one irrigation (at CRI). Thus theumber of irrigations ranged from 1 to 3 (75–225 mm), but theime of irrigation also varied.

.3.2. Soil matric potentialAs in 2006–2007, the soil dried faster in the non-mulched treat-

ent to a depth of 40 cm, after irrigation and rainfall, and theifferences decreased with depth (Fig. 6). Before the first irriga-ion (at CRI, 27 DAS), SMP was −61 kPa under non-mulched wheat

15 1522 NS

rofile).

compared with −40 kPa under mulched wheat at 10 cm depth. As in2006–2007, there was no change in SMP at depths beyond 120 cmduring the whole crop season.

3.3.3. Crop development, establishment and growthSimilar to 2006–2007, all development stages were delayed by

mulching. The crop emerged through the soil 7 DAS in non-mulchedwheat and 2 d later through the mulch (Table 2). Non-mulchedwheat took 113 d to reach 50% anthesis and 149 d to reach matu-rity, compared with 122 and 155 d, respectively, in mulched wheat.There was no effect of irrigation treatment at any crop developmen-tal stage.

Plant density (∼220 plants m−2) and uniformity of establish-ment (CV 27%) were good and similar in both mulched andnon-mulched wheat. Tiller production rate was similar in all irri-gation treatments except I3, where tiller density was significantlylower (p < 0.05) due to lack of an early irrigation (Fig. 7b). Maximumtiller density ranged from 544 to 574 tillers m−2 in all irrigationtreatments except I3 (400 tillers m−2). Treatments I1 and I2 had sig-nificantly higher maximum tiller density (around 570 tillers m−2)than all other treatments. Maximum tiller density in I1 and I2 washigher than that in 2006–2007 (525 tillers m−2). There were sig-nificant interactions between irrigation and mulch treatments ontiller density at 75, 90 and 115 DAS. At 75 (maximum tillering)and 90 DAS, tiller density was significantly higher with mulch thanwithout mulch in I3 (no irrigation at CRI). At 115 DAS, I1, I2 andI4 had significantly higher tiller density with mulch than withoutmulch.

After maximum tillering, tiller mortality was slightly higherwithout mulch (34%) than with mulch (29%) (average of all irri-gation treatments) which resulted in significantly (p < 0.05) highertiller density at harvest under mulch. Tiller mortality in I2 was 35%without mulch, less than in the previous year, and 30% with mulch,and similar tiller mortality was observed in I4 and I6 treatments.Tiller mortality was higher in I5 (38 and 31% without and withmulch, respectively) than in other treatments, which lead to sig-nificantly lower tiller density at harvest than in I1, I2, I4 and I6. Thelowest tiller mortality was observed under I3 (27 and 22% without

and with mulch, respectively). At harvest, tiller density in I3 and I5(303 and 353 tillers m−2, respectively) was significantly lower thanin the other treatments.

Initial biomass production rate was similar with and withoutmulch (∼21 kg ha−1 d−1) from sowing to 50 DAS. From mid-tillering

Balwinder-Singh et al. / Field Crops Research 121 (2011) 209–225 217

F mass2 in (c–

twcd4

TI

ig. 5. Water productivity (a) grain WPET, (b) biomass WPET, (c) grain WPI , (d) bio006–2007. Vertical bars are LSD (p = 0.05) for residue treatments in (a) and (b) and

o anthesis, biomass production with mulch was much less thanithout mulch, in contrast to the previous year. This period coin-

ided with a period of continuous low temperature and frostyays (15–30 January) and crop growth rate in I2 with mulch was3.0 kg ha−1 d−1 from 50 to 90 DAS compared to 58.0 kg ha−1 d−1

able 5rrigation application time under mulch and irrigation treatments in 2007–2008 (DAS = d

Treatments Time of irrigation appl

Irrigation Residue First

I1 Mulch 34Non-mulch 27

I2 Mulch 27Non-mulch 27

I3 Mulch 100Non-mulch 100

I3 Mulch 27Non-mulch 27

I5 Mulch 27Non-mulch 27

I6 Mulch 27Non-mulch 27

WPI , (e) grain WPI+R , and (f) biomass WPI+R of mulch and irrigation treatments inf) are for the interaction (irrigation × mulching).

without mulch. Growth rate was higher with mulch than withoutmulch after 90 DAS, resulting in similar biomass at maturity withand without mulch (9.4–9.6 t ha−1). The mean crop growth rateunder mulch from 90 DAS to maturity was 116 kg ha−1 d−1 com-pared to 100 kg ha−1 d−1 without mulch. As for tiller density, there

ays after sowing).

ication (DAS) Total irrigation (mm)

Second Third

114 – 15085 120 225

100 128 225100 128 225128 – 150128 150114 – 150114 – 150

– – 75– – 75

100 – 150100 – 150

218 Balwinder-Singh et al. / Field Crops Research 121 (2011) 209–225

20cm

Mat

ric

pote

ntia

l (kP

a)

-90

-70

-50

-30

-10

40cm

Mat

ric

pote

ntia

l (kP

a)

-90

-70

-50

-30

-10

60cm

Days after sowing

160140120100806040200

Mat

ric

pote

ntia

l (kP

a)

-90

-70

-50

-30

-10

10cm

Mat

ric

pote

ntia

l (kP

a)

-90

-70

-50

-30

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Rai

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l/Irr

igat

ion

(mm

)

10

30

50

70

90

MulchNon-mulchRain/Irrigation

F 0 ando

wtml9m

tstottl

ig. 6. Effect of mulch on soil matric potential in irrigation treatment I2 at 10, 20, 4f the means).

ere significant interactions between irrigation and mulchingreatments for biomass production at 75, 90 and 115 DAS. All

ulched irrigation treatments except I3 had significantly (p < 0.05)ower biomass than respective non-mulched treatments at 75 and0 DAS. At 115 DAS, I3 and I5 had significantly higher biomass withulch than without mulch.Biomass was similar in most irrigation treatments throughout

he season, until shortly before maturity, except for I3 which hadignificantly lower mid-season (75 DAS) biomass than all other

reatments (Fig. 8b). During the latter stages, biomass accumulationf I5 (one irrigation at CRI only) decreased relative to that of otherreatments. By maturity, total biomass in I5 was significantly lowerhan in all other treatments, and biomass in I4 was significantlyower than in I1 and I2.

60 cm depth during the 2007–2008 wheat season (vertical bars are standard errors

3.3.4. Yield and yield componentsMean yields of I1 and I2 were about 200 kg ha−1 lower than

yields of respective treatments in 2006–2007 due to fewer grainsspike−1 and lower grain weight (Table 3). There were no significant(p < 0.05) interactions between mulch and irrigation treatments onyield and all yield components, and no effect of mulching on yield(Table 3).

Irrigation scheduling had a significant effect on grain yield.Treatment I5, which received irrigation only at CRI, had signifi-

cantly (p < 0.05) lower grain yield than all the other treatments. Thelower yield was due to lower spike density, fewer grains spike−1

and lower grain weight. Treatment I4 had significantly lower grainyield than I2 and I3 due to fewer grains spike−1 and a trend forlower grain weight (compared with I3) and trends for lower spike

Balwinder-Singh et al. / Field Crops Research 121 (2011) 209–225 219

0

100

200

300

400

500

600

180160140120100806040200Days after sowing

a

Mulch

Non-mulch

0

100

200

300

400

500

600

160140120100806040200

Till

er d

ensi

ty (

m2 )

Till

er d

ensi

ty (

m2 )

b

I1 I2 I3 I4 I5 I6

F0

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am(iot

fdmiwtwnnaw

0

2

4

6

8

10

12

160140120100806040200

Bio

mas

s (t

ha-1

)B

iom

ass

(t h

a-1)

Days after sowing

Mulch

Non-mulch

0

2

4

6

8

10

12

160140120100806040200

b

a

I1

I2

I3

I4

I5

I6

Days after sowing

ig. 7. Effect of (a) mulch and (b) irrigation treatments on tiller density during 2007-8 (vertical bars are lsd (p = 0.05)).

ensity and grain weight (compared with I2) (Table 3). Yield of I3as significantly higher than yield of all other treatments except

2, and yield of I2 was significantly higher than yield of I4, I5 and6.

As in 2006–2007, the interactions between mulching and irri-ation treatments were significant at p < 0.10 for yield and all yieldomponents (Table 3). At p < 0.10, yield of I6 (missing last irriga-ion) was significantly higher with mulch than without mulch dueo higher spike density, and similar to yield of the highest yieldingreatments.

.3.5. Water use and water productivityThere was no significant (p < 0.05) interaction between mulch

nd irrigation treatments on total seasonal ET, and no effect ofulch, but irrigation treatment had a significant effect on ET

Table 4). Total ET in treatment I2 was significantly higher thann all other treatments, and ET of I1 was significantly higher thanf I4, I5 and I6. The ET of I5 was significantly lower than in all otherreatments.

Net soil water depletion between sowing and harvest rangedrom 71 to 143 mm (Table 4). Soil water depletion occurred to aepth of between 120 and 150 cm in both the mulched and the non-ulched treatments of I2 (Fig. 4b). There was a significant (p < 0.05)

nteraction between irrigation and mulching treatments on soilater depletion, as in the previous year. With SMP-based irriga-

ion scheduling (I1), soil water depletion was significantly higher

ith mulching than without mulching, reflecting the fact that theon-mulched treatment received one more irrigation. There wereo significant differences in soil water depletion between mulchednd non-mulched treatments for the other irrigation schedules. Soilater depletion with recommended irrigation management (I2)

Days after sowing

Fig. 8. Effect of (a) mulch and (b) irrigation treatments on biomass productionduring 2007-08 (vertical bars are lsd (p = 0.05)).

was significantly lower than in all other treatment combinationsexcept for I1 without mulching.

Variations in grain and biomass WPET were small (Fig. 9aand b). Grain WPET of the treatment combinations ranged from9.4 kg ha−1 mm−1 to 10.9 kg ha−1 mm−1 and biomass WPET rangedfrom 24.6 kg ha−1 mm−1 to 28.6 kg ha−1 mm−1. There were no sig-nificant interactions between mulching and irrigation treatmentson grain or total biomass WPET, and no effect of mulch. Grain WPETwas not affected by irrigation treatment except that I3 had a smallbut significantly higher grain WPET than all other irrigation treat-ments. There were significant interactions between irrigation andmulching treatments for both grain and biomass WPI and WPI+R

(Fig. 9c–f). Irrigation treatments I1 and I6 with mulch had sig-nificantly higher grain and biomass WPI and WPI+R than withoutmulch—due to reduced irrigation with mulch in I1, and higher yieldof I6 with mulch. Grain WPI and WPI+R of I5 and I3, with and withoutmulch, were significantly higher than in all other treatment com-binations due to lower irrigation, and with a greater reduction inirrigation amount than grain yield in I5.

3.3.6. Soil temperatureThere was a consistent trend for mulch to increase minimum

soil temperature and decrease maximum temperature during thefirst few weeks after sowing, with the effect declining with time.During the first 2 weeks after sowing, maximum temperature wasdecreased by an average of 4.3 ◦C and minimum temperature was

◦

increased by 1.9 C (Fig. 10a and b). Frost occurred on 15 d between11th and 31st January, and during this period, the minimum soiltemperature with mulch was usually lower than without mulch,and the difference ranged from −0.3 to −3.8 ◦C (Fig. 10c). Mulchhad no effect on maximum temperature during this period.

220 Balwinder-Singh et al. / Field Crops Research 121 (2011) 209–225

F PET, (W c-f) ar

4

4

dpgesiJtp11a

s

ig. 9. Effect of mulch and irrigation treatments on water productivity (a) Grain WPI+R under residue and irrigation treatments during 2007–2008. Vertical bars in (

. Discussion

.1. Effect of seasonal conditions on crop performance

For non-water limited treatments (I1, I2 with mulch), the mainifferences between the two seasons were the prolonged frostyeriod in January 2008 prior to anthesis, and the hot weather duringrain filling in March 2008. These pronounced temperature differ-nces led to lengthening of the vegetative period by 8–11 d, andhortening of the period between anthesis and maturity by 12–19 d,n 2007–2008 compared with 2006–2007. The cold weather inanuary 2008 reduced crop growth rate prior to anthesis, leadingo fewer grains spike−1 (Fischer, 1985). The shorter grain fillingeriod in 2008 reduced grain weight (Kuroyanagi and Paulsen,

988; Siddique et al., 1990; Stone and Nicolas, 1995; Wardlaw,994). As a result, yields of the non-water limited treatments werebout 0.4 t ha−1 lower in 2007–2008.

High temperature during the grain filling period (“terminal heattress”) is often the main limitation to wheat yield in the IGP (Joshi

b) Biomass WPET, (c) Grain WPI , (d) Biomass WPI , (e) GrainWPI+R , and (f) Biomasse LSD (p = 0.05) for the interaction (Irrigation × mulching).

et al., 2007; Sharma et al., 2002). Given that mulching delays anthe-sis in this environment, as shown by our results, it is likely to shiftthe grain filling period into warmer weather with adverse effectson grain filling and yield. Therefore, the possibility of earlier sowingwith mulching needs to be investigated.

4.2. Effect of mulch

4.2.1. Effect of mulch on soil water status and crop performanceThere was a consistent trend for similar or higher yield with

mulch, with some significant differences. Higher or similar wheatyield under rice straw mulch was also reported in other studiesin the same environment (Acharya et al., 1998; Chakraborty et al.,2008; Sharma and Acharya, 2000; Sharma et al., 2008; Sidhu et al.,

2007; Yadvinder-Singh et al., 2008). The higher yields with mulchin our experiments were probably due to increased soil water avail-ability compared with the non-mulched treatments. The soil driedfaster and to a greater degree under non-mulched than mulchedwheat after irrigation and rainfall, consistent with the findings of

Balwinder-Singh et al. / Field Crops R

Fig. 10. Soil temperature (a) maximum and (b) minimum at 5 cm depth under mulchact

oaimoti(tbtbs2

the second half of January. It is well established that frost damage

nd non mulch during 2007–2008, and (c) minimum during January 2008 (verti-al bars are standard errors of the mean). Error bars omitted from non-mulchedreatments in (a) and (b) to improve clarity.

thers (e.g. Badaruddin et al., 1999; Rahman et al., 2005; Sharmand Acharya, 2000; Sidhu et al., 2007). The SMP data suggest thatn 2007–2008, neither the mulched nor non-mulched control treat-

ent (I2) suffered from significant water deficit stress, thus yieldsf I2 with and without mulch were similar. However, in 2006–2007,he upper root zone of I2 became so dry between maximum tiller-ng and heading that the tensiometers at 10 and 20 cm broke downSMP lower than −70 kPa), while at 40 cm, SMP in the non-mulchedreatment also fell below −70 kPa before heading. This was proba-ly the cause of the much higher tiller mortality in I2 in 2006–2007

han in 2007–2008, and more so in the non-mulched treatmentecause of the greater soil drying. This led to lower (p < 0.10)pike density and yield in I2 without mulch than with mulch in006–2007.

esearch 121 (2011) 209–225 221

The benefit of mulch in conserving soil water was also reflectedin various crop parameters in other treatments exposed to waterdeficit stress at different stages in 2007–2008, for example: (i) max-imum tiller density was higher with mulch than without mulch inthe absence of irrigation at CRI (I3), (ii) tiller mortality was higherwithout mulch in treatments which received sub-optimal irriga-tion after CRI (I4 and I5), and (iii) spike density and yield of I6(missing last irrigation) with mulch and the control were similar,whereas spike density and yield of I6 without mulch were sig-nificantly (p < 0.10) lower. However, mulching only led to higher(p < 0.10) yield in I6. The results are consistent with the findings ofothers of higher tiller survival under mulch due to reduced mois-ture stress (De et al., 1983), reduced spike density and number ofgrains per spike as a result of water deficit before and/or duringspike emergence and at anthesis (Fischer et al., 1977; Thompsonand Chase, 1992), and reduced grain weight due to moisture stressduring grain filling (Karim et al., 2000; Simane et al., 1993).

4.2.2. Effect of mulch on soil temperature and crop performanceMulch suppressed maximum soil temperature, elevated mini-

mum temperature, and lowered mean daily temperature by about1.6 ◦C during the first 2 weeks after sowing, and the effect declinedwith time. These results are consistent with the findings of otherstudies in the region (Chakraborty et al., 2008; Sidhu et al., 2007;Yadvinder-Singh et al., 2008). Suppression of soil temperature isan advantage where it rises above the optimum for germinationand growth, and a disadvantage where it is below the optimum(Badaruddin et al., 1999). In low temperature conditions, suppres-sion of soil temperature can reduce emergence and retard cropestablishment and growth (Boatwright et al., 1976; Chaudhary andChopra, 1983; Chen et al., 2007; Lindstrom et al., 1976; Yunusaet al., 1994). Low soil temperature affects the development of theroot system and thus the ability to absorb water (Cochran et al.,1982) and nutrients (Chen et al., 2002), and reduces soil nitrogenavailability (Smika and Ellis, 1971).

The optimum temperature range for wheat germination hasbeen reported to be between 22.1–29.8 ◦C (Ali et al., 1994) and20–25 ◦C (Jame and Cutforth, 2004). Lindstrom et al. (1976) foundthat the rate of emergence of wheat increased as soil temperatureincreased from 5 to 25 ◦C. Average soil temperature under mulchin the first half of November in our experiment was around 18.3 ◦C,compared with 19.5 ◦C without mulch. This seemingly small tem-perature depression was apparently sufficient to retard growthand development up to anthesis. As a result, the duration of thevegetative period was increased by about 1 week each year withmulching, while the effect on the duration from anthesis to matu-rity was smaller and inconsistent. Sidhu et al. (2007) also reporteddelayed emergence by 1–2 d with mulching in Punjab. The mod-elling studies of Arora and Gajri (1998) and Timsina et al. (2008)showed considerable yield reduction if the sowing date of (non-mulched) wheat was brought forward to 10–15 October. However,perhaps the suppression of soil temperature by mulch at the time ofestablishment and during the early vegetative period could allowearlier wheat sowing.

Reduced crop growth rate and yellowing of upper leaves wasobserved in late January 2008 in mulched wheat compared with thenon-mulched treatments. This effect was widespread in mulchedwheat in both the Indian and the Pakistani Punjabs in January 2008(Sidhu, H.S., Rahman, H.M., personal communication). The reducedgrowth and yellowing was probably due to the effect of the mulchin lowering minimum soil temperature during the frosty period in

is more likely where the soil surface is insulated by a cover such asmulch, as the insulating layer prevents heat loss from the soil to thecrop canopy (Vidal and Bauman, 1996). The yellowing with mulchcould have been due to reduced soil N availability and/or uptake as

2 Crops

aElpgsg

4

wycMsflmwnlb(epjRf2sertfs

2emB

4

gfime(igi

eNorSd

4

i(SWn

22 Balwinder-Singh et al. / Field

result of lower soil temperature (Cochran et al., 1982; Smika andllis, 1971). The reduced growth prior to anthesis in the non-waterimiting mulched treatment (I1) was associated with fewer grainser spike in 2007–2008 compared with 2006–2007. The colour androwth rate of the mulched crops recovered once the temperaturetarted to increase, and biomass was not affected by mulch duringrain filling and maturity.

.2.3. Effect of mulching on plant densityIn both years, plant density (with and without mulch) was

ithin the range (80–200 plants m2) needed to achieve potentialield for semi dwarf varieties for irrigated conditions in climaticonditions similar to those of north-west India (Fischer et al., 1976;oreno-Ramos et al., 2004). The reason for the lower plant den-

ity in 2006–2007 is unknown; soil moisture was in fact moreavourable for establishment than in 2007–2008 (Fig. 4). In waterimited situations, mulch can significantly improve crop establish-

ent (Rahman et al., 2005). However, in our experiments thereas a consistent trend for lower plant density with mulching, sig-ificant in the first year, further suggesting that water was not

imiting at establishment. Lower plant density with mulching haseen reported in many studies for a range of crops including wheatBruce, 2003; Kirkegaard, 1995; Mohanty and Painuli, 2004; Swant al., 1996). Sidhu et al. (2007) showed that mulching reducedlant density of wheat at straw loads above 7.5 t ha−1 in Pun-

ab, compared with a straw load of 8–9 t ha−1 in our experiments.educed establishment under mulch can be the result of many

actors, including the physical barrier to shoot emergence (Bruce,003; Wuest et al., 2000). Some plants that emerge through the soilurface never emerge through the mulch and die, probably due toxhaustion of carbohydrate due to the inability to harvest adequateadiation because of shading by the mulch (Wuest et al., 2000). Lightransmission through wheat stubble to the soil surface declinedrom 100% for zero stubble load to 66 and 45% for 3 and 6 t ha−1

tubble loads, respectively (Rebetzke et al., 2005).Despite lower plant density at establishment with mulching in

006–2007, maximum tiller density was not affected. It is well-stablished that cereals such as wheat have the ability to produceore tillers to compensate for lower plant density (Freeze and

acon, 1990; Solie et al., 1991; Porter and Khalilian, 1995).

.2.4. Effect of mulching on irrigation and ETIn both years, SMP-based scheduling delayed the time of irri-

ation with mulch compared with no mulch, consistent with thendings of Yadvinder-Singh et al. (2008). This resulted in oneore irrigation to the non-mulched than the mulched treatment

ach year, however this is not always the case with mulchingYadvinder-Singh et al., 2008). Whether there will be a reductionn the number of irrigations as a result of both mulching and irri-ation scheduling treatments depends on the incidence of rainfalln relation to timing of irrigations.

Total ET was well within the range of ET estimated in the mod-lling studies of Timsina et al. (2008) for wheat sown around 10ovember in the same location. There was no effect of mulchingn total ET each year, although this was in fact the net result ofeduced pre-anthesis ET and increased post anthesis ET (Balwinder-ingh et al., 2010). Lascano et al. (1994) also reported no significantifference in total ET for cotton with and without mulch.

.2.5. Effect of mulching on water productivityGrain WPET using the current recommended irrigation practice

n our study is close to that of other studies in same region for wheatChakraborty et al., 2008; Choudhury et al., 2007; Jalota et al., 2006;ingh et al., 1980). Mulch significantly increased biomass and grainPET only in 2006–2007, as a result of higher yield because the

on-mulched crop suffered from water deficit stress.

Research 121 (2011) 209–225

In both years, mulch significantly increased grain and totalbiomass WPI and WPI+R with SMP-based scheduling because ofreduced irrigation amount while yield was maintained. This also ledto greater withdrawal of water from soil profile to meet ET needs.Moisture remaining in the soil profile after wheat harvest is likelyto be lost by Es because of the very high evaporative demand dur-ing the long fallow period between wheat harvest and rice planting(Humphreys et al., 2010), hence the desirability of maximising theuptake of residual soil water by wheat after rice. The fact that WPI

and WPI+R were generally higher than WPET in respective treat-ments reflects the fact that a significant amount of total ET wassupplied by residual soil water remaining in the soil after rice har-vest, plus rainfall.

4.3. Effect of irrigation scheduling

4.3.1. Effect of irrigation scheduling on irrigation amount andcrop performance

In 2006–2007, there was only one post-sowing irrigation of themulched treatment with both SMP-based scheduling (I1) and therecommended practice (I2, IW/(CPE − rain) = 0.9), while in the sec-ond year the mulched I2 received one more irrigation than I1, for thesame grain yield. In 2007–2008, the use of an IW/(CPE − rain) ratioof 0.6 reduced the number of irrigations by one compared with therecommended ratio of 0.9, but yield was significantly reduced byalmost 0.5 t ha−1, consistent with the model predictions of Timsinaet al. (2008). Prihar et al. (1976) found that irrigation schedulingof non-mulched wheat based on an IW/(CPE − rain) ratio of 0.75saved 40 mm of irrigation water without affecting yield, howeverour results suggest that, in some years, even the recommended ratioof 0.9 does not always avoid yield reducing levels of water deficitstress. Furthermore, it can result in over-irrigation of mulchedwheat. Our results also show the benefit of irrigation schedulingaccording to soil water status rather than CPE, consistent with theresults of the modelling studies of Timsina et al. (2008) using a50% soil water deficit to trigger irrigations. However, in terms ofmaximising yield while minimising irrigation input, the optimumirrigation SMP threshold has not been clearly established.

In Punjab, India, the first irrigation of wheat is recommendedat 3–4 weeks after sowing, which coincides with the time of CRI(Prihar and Sandhu, 1987). The purpose of this first irrigation isto promote tillering (Singh et al., 1987). In our study, SMP-basedirrigation scheduling delayed the first irrigation of the mulchedtreatment by about 7 d each year, with no detriment to yield.Sandhu et al. (1990) concluded that the first irrigation to wheat canbe delayed until 40 DAS without affecting tillering. In our study I3missed the irrigation around CRI all together, with the first irriga-tion 100 DAS. While this resulted in significantly lower tiller andspike density, yield was maintained as a result of more grainsspike−1 and higher grain weight. In fact, yield of I3 was significantlyhigher than yield of all other irrigation treatments except I2.

Reducing the number of irrigations to one at CRI (I5) saved150 mm of irrigation water in comparison with the control, butyield was reduced by about 25% (0.8 t ha−1). The modelling studiesof Timsina et al. (2008) suggest that if only a single post sowingirrigation is applied, yields will be maximised by applying this atbooting. In contrast, Gajri et al. (1989, 1991, 1993) reported that oneearly season irrigation at about 30 d after sowing can force the cropto use the profile water and give yields as high as that with more fre-quent irrigation. However Jalota et al. (1980) recommended at leasttwo irrigations, one at CRI and another at flowering, similar to our

treatment I6, which maintained yield with mulch, but not withoutmulch. The variable findings of the above field studies are probablydue to the different seasonal and site conditions, and point to theneed for modelling studies to take into account the range of possi-ble seasonal weather conditions. Rainfall during the wheat season

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n this region varied from close to zero (3 mm) to 250 mm from970 to 2006.

Current farmer practice is to apply 4–6 irrigations at key growthtages, however the above findings suggest that this will not nor-ally be necessary for maximum yield. Hence there is considerable

cope to help farmers to improve irrigation scheduling for wheatfter rice. The main challenge is to provide them with simple toolsr information to achieve this.

.3.2. Effect of irrigation scheduling on ET and water productivityIn 2007–2008, ET was reduced significantly through the use of

MP-based scheduling in comparison with recommended practiceI2), while maintaining yield. There was a further reduction in ET bymitting the irrigation at CRI, without loss of yield, saving 75 mmf irrigation water in comparison with I2. Even larger reductionsn ET were achieved through missing the last irrigation (I4) or onlyrrigating at CRI (I5) but at the cost of yield.

Grain and biomass WPET were similar in all irrigation treatmentsxcept I3 in 2007–2008 because assimilation and transpirationre affected to approximately to the same degree by water stressTanner and Sinclair, 1983). Consequently WPET remains more oress stable unless harvest index changes as in I3 in 2007–2008.

Grain and biomass WPI and WPI+R increased with decrease inrrigation input. However, WPI and WPI+R were also different forreatments with the same irrigation amount but at different times,ecause grain and biomass production are affected by both theuration and the time of water stress (Hussain et al., 2003). In lessrequently irrigated treatments, a larger proportion of ET was sup-lied by residual soil water and rainfall, and thus WPET was lessffected than WPI and WPI+R. Proper irrigation scheduling can besed to optimize crop yield at a given level of crop ET, leading toore yield per unit of ET. But, higher WPI and WPI+R are of no value

f associated with unacceptably low yield or unacceptably highernputs. So it is necessary to schedule irrigations to develop a betternd deeper root system to ensure that the crop extracts the maxi-um residual water from the soil profile, especially in wheat after

ice where the subsoil contains a large amount of water.Further field and modelling studies are needed to help deter-

ine the likely irrigation and ET water savings with mulching andrrigation scheduling, and the tradeoffs with yield and water pro-uctivity, as affected by site conditions (climate, soil, watertableepth) and other management practices.

. Conclusions

Mulch conserved soil water, and delayed the need for irrigation.hen irrigations were scheduled based on soil matric potential

SMP), mulching reduced the number of irrigations by one in 2ears of contrasting rainfall patterns and amount, while main-aining yield and greatly increasing irrigation water productivityWPI), in comparison with the recommended practice of schedul-ng according to cumulative pan evaporation (CPE). However, thisrrigation water saving benefit of mulching will not always be thease, depending on the incidence of rainfall. Where water was limit-ng, mulch improved crop growth and yield determining attributes,owever this only led to significantly higher yield when there wasrolonged water deficit stress prior to anthesis.

Mulch also lowered soil temperature, more so earlier in the sea-on, and extended the vegetative period by about 1 week each year.his could potentially be deleterious through pushing the grain fill-

ng period into warmer weather. However, the early cooling effectf mulch might allow earlier sowing of wheat in north-west India,nd this needs to be tested.

Using the recommended irrigation scheduling for north-westndia, based on CPE, the non-mulched wheat suffered from water

esearch 121 (2011) 209–225 223

deficit stress which led to yield reduction in one of the twoyears. Furthermore, the recommended irrigation scheduling prac-tice resulted in one more irrigation of the mulched crop each yearthan SMP-based irrigation scheduling, for the same yield. With thecurrent drive to retain rice residues on the surface instead of burn-ing them, there is a need for new guidelines for irrigation schedulingwhich take into account the availability of soil water to the crop,to capitalise on the benefits of mulching. Further field and mod-elling studies are needed to help determine optimum thresholdsfor irrigation, and to extrapolate the findings to other regions, andto convert this knowledge into practical guidelines for farmers.

Acknowledgements

We are grateful to the Australian Centre for International Agri-cultural Research (ACIAR) for support of the senior author througha John Allwright Fellowship. We thank Dr H.S. Sidhu for providingthe experimental site and the Happy Seeder and his suggestions forthe field experiment, and Messrs Sarabjit Singh and Baljinder Singhfor their excellent technical assistance.

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