Carry-over of residual soil moisture with mulching and
conservation tillage practices for sowing of rainfed
wheat (
Triticum aestivum
L.) in north-west India
Pradeep K. Sharma
*, C.L. Acharya
1Department of Soil Science, Himachal Pradesh Agricultural University, Palampur-176 062 (HP), India
Received 6 September 1999; accepted 11 July 2000
Abstract
Lack of adequate seed-zone moisture is a major problem in the timely sowing of wheat (Triticum aestivumL.) after maize (Zea maysL.) in rainfed areas of north-west India. Field experiments were conducted during 1993±1997 in an acid Al®sol (typic Hapludalf) in north-west India to conserve rainwater in situ by using four combinations of mulch and tillage practices, and using the conserved moisture for sowing of wheat at different dates. Fresh lantana (Lantana camaraL.) biomass was used as mulch during standing crop of maize before the recede of monsoon rains (LNT) or at maize harvest (LNTmh). Conservation (CT, opening of furrow with hand plough for seeding plus mulch) and conventional tillage (CC, preparation of ®ne seed-bed by digging soil to 12±15 cm depth) were the two tillage treatments. Treatment combinations during 1993 and 1994 were: LNTCT, LNTCC, LNTmhCT and CC; during 1995 and 1996, LNTmhCT was replaced with CCLNT treatment.
Wheat was sown at three dates, viz. early (S1, mid-October), timely (S2, mid-November) and late (S3, mid-December). Annual mean temperature of the area varies between 8.28C in January and 28.08C in June, and annual rainfall (1969±1997) between 1385 and 3259 mm. Mulching during standing crop of maize (LNTCT and LNTCC) was most effective in conserving rainwater. Mulching at maize harvest (LNTmhCT) is either as good or inferior to mulching in the standing crop of maize,
depending on the rainfall events. The LNTCT and LNTCC, on an average, conserved more water than CC by 7.8 mm in 0±7.5 cm soil layer and by 15.1 mm in 0±45 cm soil layer at S1, 9.2 and 22.2 mm at S2, and 7.1 and 15.0 mm at S3sowing date, respectively. The corresponding values of moisture conserved with LNTmhCT over CC were 7.4 and 8.2 mm at S1, 3.6 and 20.1 mm at S2, and 3.9 and 5.8 mm at S3, respectively. The LNTCT and LNTCC always produced signi®cantly higher wheat grain yield (0.58±2.96 Mg haÿ1
) than CC (0.36±1.78 Mg haÿ1
); except at S2during the ®rst cropping cycle where wheat yield was statistically the same with all the three treatments. The LNTmhCT and CCLNT, in general,
produced higher wheat yield than CC. The LNTCT produced signi®cantly higher wheat yield (1.93±2.84 Mg haÿ1) than
LNTCC (1.58±2.62 Mg haÿ1
) during third cropping cycle onwards, while during the ®rst two years, the yield response varied with tillage system and date of sowing. Mulching signi®cantly increased maize yield during third cropping cycle onwards. After four cropping cycles, organic carbon content in 0±15 cm soil layer of mulched plots (LNTCT, LNTCC and CCLNT) was signi®cantly higher (11.3±12.3 g kgÿ1) than control (CC) plots (9.0 g kgÿ1).#2000 Elsevier Science B.V. All rights reserved.
Keywords:Organic carbon; Maize; Moisture conservation; Mulch; North-west India; Sowing date; Tillage; Wheat
*Corresponding author. Tel.:91-1894-30382/32397; fax:91-1894-30511.
E-mail address: [email protected] (P.K. Sharma).
1Address: Indian Institute of Soil Science, Nabi Bagh, Berasia Road, Bhopal-462 038 (MP), India.
1. Introduction
Maize±wheat is an important annual cropping sequence in rainfed areas of hills and foothills of north-west India. Maize is sown by the end of May to ®rst week of June and harvested by the end of September. Monsoon rains usually recede by the second week of September. The period between Octo-ber and DecemOcto-ber most of the time is practically dry. In the absence of rains after maize harvest, the major problem in the timely establishment of spring wheat is the lack of adequate moisture in the seed zone. Some-times the sowing of wheat is delayed to as late as the second week of January. Many times the farmers practice dry seeding of wheat. The emergence and crop establishment is then dictated by the late winter rains, which are generally less than satisfactory. Late emergence adversely affects tillering, and grain yield is poor. Best wheat yields are obtained if the crop is sown in November. Wheat is harvested in April±May. The farmers in hills and foothills of north-west India generally prefer to thrash and store grains and stover of maize crop before starting the operations for wheat cultivation, especially if the soil moisture is not optimum for timely (November) sowing of wheat. In the process, residual soil moisture further declines due to evaporation. In some areas farmers go for repeated shallow tillage with countryside plough to conserve soil moisture by creating dust mulch (Sharma et al., 1990). Nevertheless, most of the times the sowing of wheat crop is delayed for want of adequate soil moisture in the seed zone.
The possibility of increasing and stabilising wheat yields in rainfed areas lies in the conservation of residual soil moisture and its carry-over for early/ timely sowing of wheat. The role of mulches and tillage practices in conserving soil moisture, with the subsequent effect on crop yields, has long been recognised (Gupta and Gupta, 1986; Grevers et al., 1986; Sharma et al., 1990). Earlier studies have shown that it is possible to conserve soil moisture by applying mulch of waste organic residues, like dry leaves of sal trees (Shorea robustaGaertn. f.) or lantana (Lantana camara L.) biomass, or eupatorium (Eupatorium adenophorumSprengel) biomass, during maize crop-ping season or at maize harvest (Sharma et al., 1990; Acharya and Kapur, 1993; Acharya et al., 1998). Mulching coupled with conservation tillage (opening
of a furrow with hand plough for seeding plus mulch) has proved better than conventional tillage (two to three ploughings with animal-drawn countryside plough) in conserving moisture and producing wheat yields (Sharma et al., 1990; Acharya et al., 1998).
In the present study, we used lantana biomass as the mulch material. Lantana is an obnoxious weed, grow-ing abundantly in waste lands and is fast encroachgrow-ing on cultivated areas. It is un®t for cattle feed but has a potential as mulch material. It contains about 51% carbon, 2.3% N, 0.22% P and 1.5% K on dry-mass basis. Hence, its use as mulch in the long-run will also improve chemical fertility of soil, in addition to moderating hydro-thermal regime for wheat cultiva-tion (Acharya et al., 1998).
The objective of the present investigation was to study the period over which rainwater conserved in the seed/root-zone during wet season with different com-binations of mulch and tillage practices can be carried-over for timely/late sowing of wheat in rainfed areas. For the in situ rainwater conservation, only those treatments were considered which had given best results in earlier studies. Reduced tillage plus mulch (i.e., conservation tillage) had given better results than reduced tillage without mulch (i.e., minimum tillage). Hence, in this study we compared only the conserva-tion tillage with convenconserva-tional tillage for moisture conservation.
2. Materials and methods
2.1. Experimental site
Field trials were conducted during 1993±1997 at the farm of Himachal Pradesh Agricultural University, Palampur (32860
N and 768320
E; 1300 m msl). The climate of the area is wet temperate characterised by severe winters and mild summers. Annual mean tem-perature varies between 8.28C in January and 28.08C during the hottest month of June. The annual rainfall varies between 1385 and 3259 mm, with an average of 2424 mm (based on rainfall data of 1969±1997). The mean relative humidity in the region varies between 46% in May and 84% in July/August.
The experimental soil (USDA: Typic Hapludalf) was silty clay loam in texture, and had 5.8 pH and 8.7 g kgÿ1
layer at the start of the experiment. The soil was low in available N and P, and medium in available K. The surface soil retained, on mass basis, 303 g kgÿ1
moist-ure at 30 kPa suction and 181 g kgÿ1
moisture at 1500 kPa suction. The experimental soil prior to the start of this experiment was being put to general cultivation of maize and wheat in an annual sequence under rainfed conditions.
2.2. Climatic water balance
Weekly rainfall and PAN-evaporation (PAN-E) data, averaged over 29 years (1969±1997), are shown in Fig. 1. According to these data, during the ®rst 12 weeks (up to third week of March) and 24 to 39 weeks of the year (mid-June±September), rainfall exceeds the evaporation, showing a positive water balance. During 12th to 24th (last week of March±mid-June), and 39th to 51st week of the year (September±third week of December), evaporation exceeds the rainfall, indicating a negative water balance. Thus, on an average, for 28 weeks in a year the climatic water balance is positive, and for 24 weeks the climatic water balance is negative. The average annual rainfall is 2424 mm, evaporation is 1290 mm, and the annual water surplus is 1134 mm.
May±June is the period of sowing of wet season crops (i.e., maize), while September±November is the period for sowing of winter crops (i.e., wheat), and
during both the periods the climatic water balance is negative. The wet season (mid-June±September) receives about 74% of the total rainfall, which amounts to about 1770 mm. It is much higher than the evaporation during this period (323 mm). Hence, there is ample scope of in situ moisture conservation during wet season for use by the succeeding winter crops in rainfed areas.
2.3. Treatments
A combination of 12 treatments, comprising mulch, tillage and date of sowing of wheat, in maize±wheat cropping sequence, were tested in 5 m3 m plots, arranged in randomised complete block design, in three replications. The treatment details are given in Table 1.
Mulching in standing crop of maize utilized fresh lantana biomass at 20 Mg haÿ1
, having 55±60% moisture content, during the last week of August (before the recede of monsoon rains), when the soil pro®le was almost saturated with rainwater. On dry-mass basis, the mulch material amounted to about 8± 9 Mg haÿ1
. Maize (cv. Parvati) was cultivated as a general crop with conventional tillage (by digging soil manually to about 15 cm depth). It received 120 N± 26 P±33 K kg haÿ1
through urea, single superpho-sphate and muriate of potash, respectively. Wheat (spring wheat) was sown with conventional and
conservation tillage. In conventional tillage, a ®ne seed-bed was prepared by digging the top 12±15 cm soil layer manually. In mulched plots, mulch material was mixed with soil during land preparation. In con-servation tillage, furrows were opened in mulched plots with a hand plough for sowing of wheat; the seeds were covered with soil manually and the lantana mulch was retained. Wheat received 120 N±40 P± 25 K kg haÿ1
in all plots as urea, single superpho-sphate and muriate of potash, respectively. All of P and K, and half of N were band placed at the time of sowing, and remaining N was applied by broadcast method in two equal splits, each at active tillering and panicle initiation stage. Plots with conventional tillage and without mulch (CC) were considered as control and other treatments were compared with this treat-ment.
2.4. Soil and crop measurements
Rainfall events during wheat cropping season were recorded in a nearby meteorological observatory and
the data are presented in Table 2. Gravimetric moisture content was determined in 0±7.5, 7.5±15, 15±30 and 30±45 cm soil layers at the time of sowing of wheat. Organic carbon (OC) content of soil in the surface 15 cm layer was determined in all plots at the end of fourth maize crop, using the rapid titration method of Walkley and Black (Jackson, 1958). Bulk density was also determined at the harvest of fourth maize crop and 30 days after sowing of wheat in 0±7.5, 7.5±15, 15± 22.5, 22.5±30 and 30±45 cm soil layers, using metal cores of 7.5 cm length and 5.3 cm diameter. Equiva-lent water depth in 0±7.5 and 0±45 cm soil layers was determined at the time of sowing of wheat. Soil temperature at 5 cm depth was recorded at 7:00 h on selected days during December and January (the coldest months) using a soil thermometer. Grain yields of maize and wheat were recorded at crop harvest.
2.5. Statistical analysis
The data on organic carbon content, bulk density, equivalent water depth in soil pro®le, and grain
Table 1
Tillage treatments in maize±wheat cropping system and sowing dates of wheat
1993 1994 1995 1996
I. Maize
Date of sowing May 29 May 28 June 16 June 15 Date of harvesting September 28 September 28 September 27 October 3 II. Wheat
Mulch and tillage treatments
LNTCT Lantana mulch (LNT) in standing crop of maize followed by sowing of wheat with conservation tillage (CT)a LNTCC Lantana mulch in standing crop of maize followed by sowing of wheat with conventional tillage (CC)b LNTmhCTc Lantana mulch at maize harvest followed by sowing of wheat with conservation tillage
CC Sowing of wheat with conventional tillage
CCLNTc Sowing of wheat with conventional tillage followed by LNT mulch
Date of sowing
1993±1994 1994±1995 1995±1996 1996±1997 S1: early sowing
(cv. VL 616)
October 8 October 8 October 6 October 9 S2: timely sowing
(cv. HS 240)
November 11 November 12 November 15 November 11 S3: late sowing
(cv. HPW 42)
December 23 December 22 December 23 December 17
aFurrows were opened in mulched plots with a hand plough for sowing of wheat; the seeds were covered with soil manually and the lantana mulch was retained.
bFine seed-bed was prepared by digging the top 12±15 cm soil layer manually; in mulched plots, mulch material was mixed with soil during land preparation.
cThe treatment `LNT
yield were analysed by analysis of variance in rando-mised complete block design. Soil temperature with and without mulch was compared by using paired
t-test.
3. Results and discussion
3.1. Soil organic carbon
Soil incorporation of lantana (LNTCC) or its application as surface mulch (LNTCT, LNTmh
CT=CCLNT) continuously for four years signi®-cantly increased soil OC in the plough layer (0±15 cm depth), but not in the subsoil (Table 3). Similar observations were made in another experiment invol-ving rice±wheat cropping sequence, where lantana
was applied to rice crop at the rates of 10±30 Mg haÿ1
per year (on fresh mass basis) for six years (Sharma et al., 1995). Bhagat and Verma (1991) also reported signi®cant build-up in soil OC in the plough layer with rice straw applications for ®ve years in a soil under rice±wheat cropping under the same environmental conditions. These data show that the downward move-ment of OC from surface applied organic residues is very slow. Increase in soil OC in the surface layer due to four annual lantana applications at the rate of 20 Mg haÿ1
was around 25±35% over the control. Tillage treatments did not affect soil OC signi®-cantly, although OC values with conservation tillage were numerically higher than with conventional til-lage (Table 3). Tiltil-lage effects on soil OC may become signi®cant when tillage is practised over a longer period of time.
Table 2
Rainfall events during wheat cropping season at Himachal Pradesh Agricultural University, Palampur, in north-west India Period Rainfall (mm)
1993±1994 1994±1995 1995±1996 1996±1997
Maize harvest to S1 5.1 0 20.5 14.6
S1to S2 21.5 4.3 6.8 2.3
S2to S3 0 22.8 8.8 9.4
S1to wheat harvesta 294.7 297.9 245.0 229.1 S2to wheat harvestb 273.2 293.6 238.2 226.8 S3to wheat harvestc 273.2 270.8 229.4 217.4
aEarly sowing of wheat. bTimely sowing of wheat. cLate sowing of wheat.
Table 3
Soil organic carbon (OC) and bulk density under different treatments (1996±1997)
Treatmentsb OC (g kgÿ1)a Bulk density (Mg mÿ3) 0±15 cm
(g kgÿ1)
15±30 cm (g kgÿ1)
0±15 cm (Mg haÿ1)
15±30 cm (Mg haÿ1)
At maize harvest At 30 DAS of wheat 0±7.5 cm 7.5±15 cm 0±7.5 cm 0±7.5 cm LNTCT 12.3 8.1 24.2 16.9 1.31 1.32 1.31 1.34 LNTCC 12.0 7.9 23.4 16.6 1.30 1.31 1.23 1.26 CCLNT 11.3 8.0 22.0 16.7 1.29 1.32 1.25 1.27
CC 9.0 7.8 18.4 16.4 1.36 1.37 1.24 1.25
LSD (0.05) 1.1 NSc 2.2 NS 0.04 0.04 0.03 0.05 aAt maize harvest.
3.2. Soil bulk density
At the time of maize harvest, bulk density in 0±7.5 and 7.5±15 cm soil layers of lantana-treated plots (LNTCT, LNTCC and CCLNT) was signi®-cantly lower than in control (CC) plots (Table 3). Bulk density was negatively correlated with soil OC (r ÿ0:701,P0:05) (Fig. 2), and lantana-treated plots had signi®cantly higher soil OC. Signi®cant negative correlation between bulk density and OC has also been reported in earlier studies (Sharma and Aggarwal, 1984; Sharma et al., 1995). Acharya et al. (1998), in a similar study, reported increased earthworm activity in lantana-treated plots, which can also lower bulk density of soil. In this experiment, however, we did not study the effect of lantana on earthworm activity.
At 30 DAT, bulk density with conventional tillage was signi®cantly lower compared to conservation tillage, irrespective of lantana treatment. This occurred because of the tillage operations performed for preparing seedbed for wheat, which loosened the soil and decreased bulk density. Tillage masked the effect of soil OC on bulk density. Mulch and tillage treatments, however, did not affect bulk density below 15 cm soil depth. The average bulk density in 15±45 cm soil layer varied between 1.39 and
1.43 Mg mÿ3
, indicating the presence of a relatively compact subsoil layer.
3.3. Soil temperature
The minimum soil temperature at 5 cm depth, recorded on selected days during December and January, 1996±1997, was 0.5±28C higher under lantana mulch than in control, and the differences were statistically signi®cant (Table 4). Similar obser-vations were made by Acharya et al. (1998). Under conditions of suboptimal thermal regime, increase in
Fig. 2. Relationship between organic carbon (OC) content and bulk density of soil.
Table 4
Effect of lantana mulch on minimum temperature of soil at 5-cm depth (1996±1997)t-value14df2:257
Date Soil temperature (8C) at 7 a.m. No mulch Mulch
December 4 6.5 8.5
December 11 5.5 7.0 December 18 4.0 4.5 December 27 4.5 6.0
January 3 3.0 4.5
January 10 3.5 5.0
January 21 4.5 5.5
January 28 5.5 7.0
soil temperature even by 0.5±28C signi®cantly affects wheat growth and yield.
3.4. Moisture conservation
Seed zone (0±7.5 cm) as well as root-zone (0±45 cm) moisture contents at the time of sowing of wheat crop were signi®cantly higher in mulched than in unmulched plots (Table 5). Mulching during standing crop of maize was either superior or equal to mulching at maize harvest, depending on rainfall pattern, in conserving soil moisture. Tillage treatments (LNTCT and LNTCC) did not differ signi®cantly in their effect on seed-zone moisture content, but root-zone moisture content was sometimes higher with conservation than conventional tillage (Table 5). Soil moisture conserved with mulching could be carried-over even for late sowing of wheat in the third week of December. Mulch applied after the sowing of wheat (CCLNT) prob-ably affected wheat yield more through temperature moderation rather than moisture conservation.
According to these data, mulching was more effec-tive in conserving rainwater in situ when applied during standing crop of maize before the recede of monsoon rains. During this period, the soil pro®le is almost saturated with water. In wet soils, the evapora-tion rate is weather controlled. Applicaevapora-tion of mulch at this stage reduces evaporation ¯ux, and gives more time for the water to redistribute within soil pro®le (Hillel, 1980). If soil pro®le is wet at the time of maize harvest due to late recede of monsoon rains, mulching at maize harvest also will be equally effective in moisture conservation. During fallow period (between maize harvest and sowing of wheat), mulch helps in the conservation of water received from intermittent rain showers, if any, and maintains optimum moisture in the seed zone.
3.5. Wheat yield
Changes in residual soil moisture storage caused by different mulch and tillage treatments were
signi®-Table 5
Pro®le water content under different treatments at the time of sowing of wheat Sowing
date
Mulch and tillage treatmentsa
Equivalent water depth (mm)
Seed zoneb Root zonec
1993±1994 1994±1995 1995±1996 1996±1997 1993±1994 1994±1995 1995±1996 1996±1997 S1 LNTCT 23.2 18.3 25.9 32.4 153.5 113.2 158.2 174.1
LNTCC 22.5 16.9 26.2 32.4 146.6 110.1 156.7 169.7 LNTmhCT 21.5 17.2 ± ± 141.3 109.7 ± ±
CC 14.2 9.7 22.0 21.9 131.9 102.6 145.6 150.8 CCLNT ± ± 21.6 20.8 ± ± 145.1 160.4 LSD (0.05) 1.9 2.3 1.9 2.9 3.1 3.9 2.9 3.3 S2 LNTCT 22.1 16.8 19.2 21.6 137.3 137.0 134.4 138.3 LNTCC 21.6 16.5 18.5 18.7 136.6 136.0 133.1 124.8 LNTmhCT 18.6 10.3 ± ± 137.7 133.0 ± ±
CC 17.6 4.1 9.8 9.3 132.4 98.0 105.2 113.0
CCLNT ± ± 8.7 10.3 ± ± 104.8 112.3
LSD (0.05) 2.3 2.8 3.0 2.7 3.9 3.8 2.7 3.1 S3 LNTCT 15.1 22.6 19.5 13.6 110.6 152.7 137.9 109.7 LNTCC 14.6 22.6 17.9 13.1 110.0 149.6 132.9 108.6 LNTmhCT 12.1 23.8 ± ± 109.8 151.5 ± ±
CC 6.6 21.5 8.9 4.1 100.6 149.2 110.1 86.3
CCLNT ± ± 10.0 4.3 ± ± 107.3 85.9
LSD (0.05) 1.9 1.3 2.1 1.8 2.2 3.4 2.8 3.1 aSee Table 1 for description of tillage treatments.
cantly re¯ected in the grain yield of wheat (Table 6), which was signi®cantly higher in mulched than in unmulched control plots (CC). Mulching after the sowing of wheat (CCLNT) also gave higher yield than the control (CC). During the ®rst year of experimentation (1993±1994), tillage treatments (LNTCT and LNTCC) did not show signi®cant difference in grain yield, but in the subsequent years in six out of nine cases conservation tillage (LNTCT) was superior to conventional tillage (LNTCC). During 1993±1994, wheat crop was damaged by hail storm at the time of its harvest, thus, producing a low grain yield.
Wheat yields with mulching during standing crop of maize (LNTCT and LNTCC) during different years were 1.5±2.4 times higher, with mulching at maize harvest (LNTmhCT) were 1.28±1.51 times
higher, and with mulching after the sowing of wheat (CCLNT) were 1.14±1.61 times higher than that of control (CC). On average, LNTCT was better than LNTCC. LNTCT produced 1.6±2.4 times higher wheat yield than CC, while LNTCC pro-duced 1.5±2.1 times higher wheat yield than CC.
Crop yield under rainfed conditions depends largely on the pro®le-stored available water at the time of sowing and the seasonal rainfall (Sharma and Kharwara, 1990). Application of mulch improved the seed-zone and root-zone moisture status, and raised the minimum soil temperature. Both the changes bene®ted wheat yields. Acharya et al. (1998) also reported that mulching under similar environment improved wheat yields by suitably mod-ifying moisture and temperature regimes of soil. In addition to improving moisture and temperature regimes, mulching with lantana biomass also added plant nutrients to soil. They bene®t wheat crop.
The effect of moisture conservation through mulch applied in the standing crop of maize (LNTCT and LNTCC) on wheat yield sown at different dates depended on the rainfall events. Early/timely sowing of wheat was better than late sowing if rains occurred after maize harvest, but failed between third week of October and December, as during 1995±1996 (Table 2). During this season, early and timely sowing, on an average, produced 1.0 and 1.3 times more wheat yield than late sowing. During 1994±1995,
Table 6
Effect of mulch and tillage treatments on grain yield (Mg haÿ1) of rainfed wheat sown at different dates Sowing date Treatmentsa
LNTCT LNTCC LNTmhCT CC CCLNT LSD (0.05) 1993±1994
S1b 0.63 0.67 0.55 0.36 ± 0.18
S2c 0.57 0.52 0.44 0.42 ± NS
S3d 0.60 0.58 0.53 0.42 ± 0.17
1994±1995
S1b 1.92 1.71 1.31 1.10 ± 0.20
S2c 1.83 2.14 1.77 1.09 ± 0.18
S3d 2.87 2.96 2.86 1.75 ± 0.16
1995±1996
S1b 1.96 1.64 ± 0.78 1.47 0.22
S2c 2.31 2.08 ± 0.91 1.35 0.17
S3d 1.93 1.58 ± 0.86 1.29 0.20
1996±1997
S1b 2.69 2.60 ± 1.29 1.40 0.17
S2c 2.80 2.62 ± 1.16 1.48 0.17
S3d 2.84 2.62 ± 1.78 1.96 0.19
aSee Table 1 for description of tillage treatments. bEarly sowing of wheat.
when rains failed between maize harvest and second week of November, but occured after second week of November (i.e., after the timely sowing of wheat), late sowing produced 1.6 and 1.5 times more wheat yield than early and timely sown wheat. During 1996±1997, wheat yields were almost the same at all the three sowing dates. But without moisture conservation, late sown wheat produced higher grain yield than early and timely sown wheat, except during 1993±1994 and 1995±1996 when timely sown wheat was as good or superior to late sown wheat.
It is important to consider the yield potential and sensitivity to hydrothermal regimes of wheat cultivars recommended for different dates of sowing while studying their response to moisture conservation treat-ments. The cultivars recommended for early (VL 616) and timely (HS 240) sowing had higher yield potential than the late sown cultivar (HPW 42). If early/timely sown cultivars have optimum soil moisture until December, they would yield better than late sown cultivar. If, on the other hand, early/timely sown cultivars experience moisture stress in the early growth phase, they would produce lower yields than late sown wheat. The yield differences between treat-ments of with (LNTCT and LNTCC) and with-out moisture conservation (CC) narrowed with the delay in sowing date. The yield differences, on an average (data for the year 1993±1994 not included because the crop was damaged with hail storm), were 1.34, 1.22 and 1.02 Mg haÿ1
at S1, S2and S3sowing
dates, respectively (Table 6). It may suggest that the late sown cultivar was less sensitive to hydrothermal regime than the early and timely sown cultivars.Ne-vertheless, grain yields of wheat with moisture con-servation (LNTCT and LNTCC) were always higher than without moisture conservation (CC). These data suggest that wheat yields under rainfed conditions can be improved with conservation tillage and mulching, but the conserved moisture should be used for sowing of wheat as early as possible. Delayed sowing may become risky if rains fail after maize harvest and until December.
3.6. Maize yield
Application of mulch, irrespective of method of application, also increased maize yield, grown in sequence with wheat. The increase in maize yield
was recorded after two cropping cycles (Table 7). Increase in maize yield could be attributed to the improvement in soil physical and chemical properties of soil due to lantana additions. Improvement in soil physical properties due to soil incorporations of organic residues is well documented in literature. In ®ne-textured soils, build-up in soil OC content with additions of organic residues improves water trans-mission and drainage conditions of soil by increasing soil aggregation and inter-aggregate pore spaces (Sharma and De Datta, 1994). Maize is very sensitive to excess water condition. Water stagnation in the root-zone even for few hours can severely damage maize crop (Sharma, 1992). Further, lantana biomass at the rate of 8 Mg haÿ1
(on dry-mass basis) would add about 184, 18 and 120 kg haÿ1
N, P and K, respec-tively, to soil every year. As the amount of chemical fertilizers applied to each plot was the same and independent of mulch application, the additional nutri-ents supplied through lantana biomass must have contributed to the increase in maize yield in mulched plots.
4. Conclusions
Establishment of wheat crop under rainfed envir-onments is possible by conserving soil moisture with the application of waste organic residues, like lantana, during the standing crop of maize, preceding wheat and before the recede of monsoon rains. The con-served soil moisture should be utilized for the early sowing of wheat, although it can be carried-over for the timely and late sowings, provided the soil moisture is supplemented with rainfall events, may be of light
Table 7
intensity, during the fallow period between maize harvest and sowing of wheat. Conservation tillage produced wheat yields higher or similar to those with conventional tillage, and may have advantage over conventional tillage in terms of time and energy required in land preparation. Use of lantana biomass as mulch material also improved maize yield. Lantana is an obnoxious weed, has little alternate uses as fodder and fuel, and is easily available locally. It can be conveniently used as mulch material. Its long-term use as mulch will not only improve soil productivity under maize±wheat cropping in rainfed environments by way of adding organic carbon and other plant nutrients, but will also keep a check on its spread to other cultivable areas. Other organic residues growing on waste lands and having less alternate uses may also be used as mulch.
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