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Effect of leucaena mulch on soil-water use and wheat yield
Agricultural Water Management 35 Ž1998. 191–200
Effect of leucaena mulch on soil-water use and wheat yield N.K. Sharma a
a,)
, P.N. Singh b, P.C. Tyagi a , S.C. Mohan
a
Central Soil and Water ConserÕation Research and Training Institute, Dehradun-248 195, India b Indian Institute of Sugarcane Research, Lucknow-226002, India Accepted 14 October 1997
Abstract A study was undertaken to assess the effects of levels and timings of incorporation of leucaena w Leucaena leucocephala ŽL.. de Witx leaf mulch on soil-water use and performance of wheat ŽTriticum aestiÕum L.. grown on Dhoolkot silty clay loam soil in submontane northwest India. Air-dried leucaena leaves were applied as a surface mulch, at the rate of 0 ŽNo mulch., 2, 4 and 6 t hay1 as main plot treatments and its timings of soil incorporation namely: immediately, 15, 30 and 45 days after harvest of maize crop as subplot treatments. Each treatment was replicated four times in a strip-plot design. The results revealed that more moisture was available in mulched surface soil Ž0–15 cm. at the time of wheat sowing. Application of mulch increased moisture extraction, water use efficiency ŽWUE., grain and straw yield of wheat crop. Incorporation of leaf mulch at 30 days after harvesting of maize crop conserved more moisture for wheat sowing. This study indicated that optimal mulch application rate was 2 t hay1 and time of incorporation was at 30 days after maize harvest. q 1998 Elsevier Science B.V. Keywords: Organic mulch; Soil-moisture conservation; Water use; Wheat yield
1. Introduction Wheat is one of the staple rainfed winter season Ž rabi . food crops of the northwest submontane region of India. Yield is generally low because of early recession of the monsoon, resulting in low residual soil moisture during October–November, coinciding with the time of seeding and germination of wheat crop ŽSingh et al., 1981.. Besides, )
Corresponding author.
0378-3774r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 3 7 7 4 Ž 9 7 . 0 0 0 4 7 - 4
192
N.K. Sharma et al.r Agricultural Water Management 35 (1998) 191–200
drought spells during the crop season also cause severe moisture stress in the soil profile, particularly at critical growth stages of the wheat crop. Consequently, there is need for conserving soil moisture to avert moisture deficit at the time of sowing and also during crop-growth period. Earlier research has revealed that use of organic mulch helps in improving crop production through moisture conservation. It has also been reported that the beneficial effect of organic mulches is mainly due to reduced evaporation ŽRajput and Singh, 1970; Singh and Bhushan, 1978; Bhushan and Ghosh, 1982; Aggarwal et al., 1992.. Incorporation of organic matter has been reported to augment water retention capacity by improving the structure and physical environment of soil ŽHussain et al., 1988; Tomar et al., 1992.. Leucaena leucocephala ŽL.. de Wit, having very high biomass production ŽAnonymous, 1977; Krishnamurthy and Mune Gowda, 1982. and fast decomposition characteristics ŽMittal et al., 1992., can be used effectively as organic mulch. Leucaena leaves may be applied in the field just after maize harvesting initially to conserve soil moisture for proper germination of the subsequent wheat crop and later incorporation in the soil at a suitable time to enhance the moisture retention capacity during crop-growth period. It is appropriate, therefore, to determine the optimum quantity of leucaena leaves required for mulching and optimum time for mulch incorporation so as to conserve and improve the soil moisture for wheat crop production. Accordingly, a systematic field study was carried out.
2. Materials and methods 2.1. Experimental site A field study was carried out for 3 years Ž1990–1991 to 1992–1993. at the Selakui Research Farm, Central Soil and Water Conservation Research and Training Institute, Dehradun, India. The soil of the experimental area belongs to the Dhoolkot series ŽBhardwaj and Singh, 1981.. Soil was analyzed using standard chemical procedures ŽJackson, 1967.. Mechanical analysis showed that the soil was silty clay loam type and contained 37% silt, 40% sand and 23% clay. Soil-moisture characteristics indicated a permanent wilting point at 11.4%, field capacity at 27% with an average bulk density of 1.44 g ccy1 of surface Ž0–15 cm. layer. Soil pH was 5.2 and it contained 0.59% organic carbon, 0.066% total nitrogen, 31 kg hay1 available phosphorus and 165 kg hay1 available potassium. 2.2. Water use and water use efficiency Soil moisture was determined gravimetrically, using a core sampler. Soil samples for moisture content determination were collected from each plot in all the replications up to the depth of 75 cm. Soil samples were taken from 0–15, 15–30, 30–45 and 45–75 cm
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soil depths for moisture determination. Soil samples for moisture content were taken at the time of sowing and harvesting of wheat crop for profile moisture extraction. Soil samples were also taken before each rainfall event to determine soil moisture deficit for calculating the effective rainfall. The water use by the crop was calculated by the following formula: Water Use Ž mm . s Soil moisture Ž mm . at the time of crop sowing ysoil moisture Ž mm . at the time of crop harvest q Effective rainfall Ž mm . . Here, water use is referred to as evapotranspiration ŽET.. Soil moisture retained within 0–75 cm soil profile, to be used by the crop, was taken as effective rainfall in calculating layer-wise water use during the crop-growing period. For this purpose, moisture data for each soil layer of root zone were used. To determine effective rainfall, the moisture deficit in different soil layers of root zone on the day of precipitation was calculated based on the moisture depletion for the preceding day. To calculate the moisture depletion, soil samples were taken before each rainfall event. Afterwards, the known amount of precipitation was distributed to meet the moisture deficit up to the field capacity level in different layers, while the excess was taken as deep percolation. Potential ET was estimated from meteorological data using modified Penman equation ŽDoorenbos and Pruitt, 1977.. Water use efficiency ŽWUE. of the crop was computed using the following equation ŽViets, 1962.: WUE s YrET where WUE s kg hay1 mm water used, Y s yield of total dry matter or grain Žkg hay1 ., ET s evapotranspiration Žmm., water expenses. 2.3. Field experimentation After taking a uniform maize crop every year in the rainy season Ž kharif ., mulching treatments were imposed soon after maize harvest by early October. The experiment was laid out in strip-plot design with three replications. The treatments consisted of four levels of mulch material Žair-dried leucaena leaves., viz., no mulch Ž M0 ., 2 Ž M1 ., 4 Ž M2 . and 6 Ž M3 . t hay1 as main treatments and four timings of incorporation of the mulch material as subtreatments, viz., 0 Žimmediately after harvest, T1 ., 15 ŽT2 ., 30 ŽT3 . and 45 ŽT4 . days after maize harvest. The mulch was incorporated evenly in the soil of the experimental plot with the bullock drawn mould board plough. Wheat was seeded with seed drill every year by the third week of November in rows 22.5 cm apart. Nitrogen, phosphorus and potash were applied to wheat in the form of chemical fertilizers at the rate of 60, 40, 20 kg hay1 , respectively. Evaporation was measured on standard USWB open pan class A. Data on rainfall and evaporation ŽTable 1. corre-
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Table 1 Rainfall and evaporation for experimental period Period
Rainfall Žmm.
Evaporation Žmm.
1990–1991 1991–1992 1992–1993 1990–1991 1991–1992 1992–1993 Maize growing 1209.5 935.2 Mulch 146.0 12.1 Wheat growing 274.9 166.7 Up to 30 DAS of wheat crop 137.0 Ž50. 0.0 Ž0.
1042.8 21.0 195.0 12.4 Ž6.
449.4 143.7 362.1 45.6 Ž13.
434.2 137.9 373.4 41.2 Ž11.
458.8 136.0 366.0 49.1 Ž13.
Figures in parenthesis are percentages of total crop-growth period. DASsdays after sowing.
sponding to the period of experimentation in each year were taken from the meteorological observatory of the Research Farm.
3. Results and discussion 3.1. Soil moisture at sowing time Data on soil moisture as affected by mulch level and incorporation timings, are presented in Fig. 1. It was found that by mulching, more moisture was available in the upper soil layer Ž0–15 cm. for wheat sowing. Similar results were reported by Singh et al. Ž1967. and Singh and Bhushan Ž1978.. The highest percentage of moisture Ž13%. was conserved when the soil surface was kept covered with mulch up to 30 days after maize harvest, whereas the lowest Ž11.5%. was conserved when mulch was incorporated into soil soon after maize harvest. This may be due to variation in period of mulch coverage over soil surface. Furthermore, lower soil moisture was observed at the time of wheat sowing when mulch was incorporated after 45 days as compared to 30 days after maize harvesting. This is perhaps due to the fact that leucaena mulch loses its effectiveness, especially when the material is not wetted by rain ŽBudelman, 1988., and the half-life value of fresh leucaena pruning is not much longer than 3 weeks ŽRead et al., 1985..
Fig. 1. Surface soil moisture Ž0–15 cm. at wheat sowing as influenced by mulch levels and timings of incorporation. M0 s 0 t hay1 ; M1 s 2 t hay1 ; M2 s 4 t hay1 ; M3 s6 t hay1 ; T1 s Immediate; T2 s15 days; T3 s 30 days; T4 s 45 days.
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Fig. 2. Mean soil water extraction pattern Žmm. under wheat as influenced by mulch levels: M0 s 0 t hay1 ; M1 s 2 t hay1 ; M2 s 4 t hay1 ; M3 s6 t hay1 .
3.2. Soil moisture extraction pattern Data relating to moisture extraction pattern of the soil profile Ž0–75 cm. for each mulch level Žmean values of four dates of application. are depicted in Fig. 2. It was revealed that in case of no mulch treatment, 57% of total extracted moisture was used from 0–30 cm soil layer by the wheat crop. However, the mulch levels of 2, 4 and 6 t hay1 increased soil moisture extraction by the wheat crop to the extent of 60, 61 and 63%, respectively. Thus, it may be inferred that even a low quantity of leucaena leaf mulch Ž2 t hay1 . may contribute towards increased soil moisture extraction from surface layer. It was also observed that the duration of spread of mulch prior to incorporation in soil induced better moisture storage during the relatively dry year Ž1991–1992. as compared to normal rainfall years Ž1990–1991 and 1992–1993.. 3.3. Water use and water use efficiency Data on actual ET requirements of crop and potential ET are given in Tables 2 and 3, respectively. It was found that water use was considerably influenced by seasonal rainfall and levels of mulch. In high rainfall year Ž1990–1991. with 275 mm of rainfall during the crop season, higher utilization of water was noticed compared to lesser rainfall years Ž1991–1992 and 1992–1993.. The potential ET was, however, not found to vary much over the three-year period. As evident from the average data in Table 3, the increasing trend of actual water use ŽET. and ratio of actual water use and potential ET ŽETrETp ., has been observed with the increase in mulch rate from 2 to 6 t hay1 . However, in the initial two years the mulch treatment did not exhibit any consistent trend in the water utilization. It might be due to the fact that the mulch effect was visible only after a few years which resulted in improvement of soil properties ŽLal, 1989.. A similar trend was observed in the case of WUE. It is evident from Table 2 that WUE was decreased due to higher utilization of water in high rainfall year Ž1990–1991., as compared to lesser rainfall years Ž1991–1992 and 1992–1993.. Significantly higher WUE was observed in mulched treatments as compared to no mulch treatment. Maximum WUE was observed with 6 t hay1 mulch level in all the years but statistically at par with that of 4 t hay1 mulch level.
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Grain yield Žkg ha y1 .
1990–1991 1991–1992 1992–1993 1990–1991 1991–1992 1992–1993 1990–1991 1991–1992 1992–1993 1990–1991 1991–1992 1992–1993
0 Ž M0. 2 Ž M 1. 4 Ž M2. 6 Ž M 3. LSD Ž P s 0.05 .
3059 3726 3871 4215 345
2421 2924 3063 3161 112
Evapotranspiration Žwater use . Žmm .
Water use efficiency Žkg ha y1 mm y1 . Rate of water use Žmm day y1 .
Mulch level Žt ha y1 .
2343 2972 3372 3495 151
329.1 360.8 358.9 367.9 23.7
244.3 248.4 246.9 250.7 66.7
241.0 242.4 259.5 265.7 20.7
9.30 10.33 10.79 11.46 1.02
9.91 11.77 12.41 12.61 0.51
9.72 12.26 12.99 13.15 0.62
2.19 2.40 2.39 2.45 0.01
1.60 1.63 1.62 1.65 0.01
1.60 1.61 1.72 1.76 0.01
Table 3 Relationship between actual evapotranspiration and potential evapotranspiration as influenced by different levels of mulch Treatment
1990–1991 ET
ETp
ETrETp
ET
ETp
ETrETp
ET
ETp
ETrETp
ET
ETp
ETrETp
0 2 4 6
329.1 360.8 358.9 367.9
410.5 410.5 410.5 410.5
0.801 0.879 0.874 0.896
244.3 248.4 246.9 250.7
421.6 421.6 421.6 421.6
0.579 0.589 0.586 0.595
241.0 242.4 259.5 265.7
442.5 442.5 442.5 442.5
0.545 0.548 0.586 0.600
271.5 283.9 288.4 294.8
424.9 424.9 424.9 424.9
0.639 0.668 0.679 0.694
Ž M0. Ž M 1. Ž M2. Ž M 3.
1991–1992
ET sevapotranspiration Žmm. Žactual water use.. ETp s potential evapotranspiration Žmm..
1992–1993
Average Ž1990–1991 to 1992–1993 .
N.K. Sharma et al.r Agricultural Water Management 35 (1998) 191–200
Table 2 Grain yield, water use, water use efficiency and rate of water use as influenced by mulch levels
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Fig. 3. Relationship between mean water use and grain yield of wheat in respect of different mulch levels: ŽObserved.. Ž(. No mulch, Ž Ø . Mulch 2 t hay1 , Ž`. Mulch 4 t hay1 , Ž^. Mulch 6 t hay1 . Regression analysis Ž(. No mulch Ž M0 . Y s1088.20q56.28xŽ R 2 s 0.58. ŽØ. Mulch @ 2 t hay1 Ž M1 . Y s1781.00q51.13xŽ R 2 s 0.68. Ž`. Mulch @ 4 t hay1 Ž M2 . Y s1761.70q58.00xŽ R 2 s 0.77. Ž^. Mulch @ 6 t hay1 Ž M3 . Y s1165.24q82.90xŽ R 2 s 0.83.
Response of wheat grain yield to water use was estimated through linear regression equations. These equations indicated that with the increase of mulch level, WUE increased as was evident from improvement of R 2 from 0.58 Ž M0 . to 0.83 Ž M3 .. Response surface curves, presented in Fig. 3 also indicated the efficacy of mulch levels. Thus, response surface curves with mulch are always above those without mulch treatment. This may be due to improvement in soil environment by use of organic mulches, which promoted root growth and eventually water absorption. This is in accordance with the findings of Chaudhary and Prihar Ž1974. and Gupta Ž1991.. 3.4. Yields Wheat grain and straw yields were significantly Ž P - 0.05. influenced by mulch levels and timings of incorporation of mulch. Highest mean grain yield Ž3623 kg hay1 . and straw yield Ž5560 kg hay1 . were recorded in the plots which received mulch level of 6 hay1 . On the other hand, lowest grain yield Ž2607 kg hay1 . and straw yield Ž4548 kg hay1 . were recorded in plots with no mulch. Yield comparison for individual years revealed that yields due to mulching were found significantly Ž P - 0.05. higher than the control during all the years. However, in the year 1990–1991 Ža high winter rainfall
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Table 4 Wheat yield as influenced by the mulch levels and days of incorporation Treatment
Grain yield Žkg hay1 .
Straw yield Žkg hay1 .
1990–1991 1991–1992 1992–1993 Mean 1990–1991 1991–1992 1992–1993 Mean Mulch leÕel (t ha y 1) 0 Ž M0 . 3059 2 Ž M1 . 3726 4 Ž M2 . 3871 6 Ž M3 . 4215 LSD Ž P s 0.05. 345
2421 2924 3063 3161 112
2343 2972 3372 3495 151
2607 3207 3435 3623 236
5638 6356 6423 6971 749
4156 4990 5096 4940 321
3852 4516 4622 4769 297
4548 5287 5380 5560 333
Days of incorporation after spread of mulch 0 a ŽT1 . 3703 2641 2911 15 ŽT2 . 3859 2900 3119 30 ŽT3 . 3626 2989 3078 45 ŽT4 . 3681 3038 3074 LSD Ž P s 0.05. NS 58 NS
3085 3292 3231 3297 NS
6245 6497 6289 6356 NS
4648 4671 4891 4981 NS
4540 4360 4417 4442 NS
5141 5176 5199 5259 NS
NSs Nonsignificant. a Immediate incorporation.
year., the yield differences due to mulch levels were found nonsignificant. During the year 1991–1992 Ža dry year., wheat grain yield achieved due to 4 t hay1 mulch, was significantly Ž P - 0.05. higher than the yield due to 2 t hay1 . Yield differences due to 4 t hay1 and 6 t hay1 mulch levels were observed nonsignificant. Similar yield trend was observed in the crop year 1992–1993 with moderate rainfall. Nonsignificant differences in mean grain and straw yields were recorded due to different levels of mulch which has shown the importance of mere coverage of soil surface that reduced the evaporation from the soil surface. Similar results were obtained with cowpea and eggplant ŽDaisley et al., 1988.. Similarly for maize crop, about 3 t hay1 of fresh leaves of leucaena were recommended as an organic manure for optimum production ŽAnonymous, 1985.. Effect of mulch incorporation timings on the yield was influenced by the seasonal rainfall. Significant differences in yield were observed ŽTable 4. only in low rainfall year Ž1991–1992. as compared to 1990–1991 and 1992–1993. Amount of seasonal rainfall particularly within 30 days after sowing of wheat crop also influenced the wheat yield. It is inferred from the above discussion that in order to maximize the wheat production, mulching of dry leucaena leaves at the rate of 2 t hay1 appears quite adequate.
4. Conclusions The study indicates that leucaena which is a promising source of leaf biomass having high nutritive value can be used effectively as organic mulch in rainfed agriculture. Data from the study suggest that by applying leucaena leaves as a mulch, soil moisture losses due to evaporation can be reduced which ensure the availability of moisture for wheat germination and subsequent crop growth. In order to obtain maximum WUE, and grain
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and straw yield of wheat, soil surface should be covered uniformly with leucaena leaf mulch at the rate of 2 t hay1 immediately after maize harvest and should be incorporated into the soil after allowing it to remain at the soil surface for 30 days. The findings of the study are promising to improve and stabilize the production of rainfed wheat.
Acknowledgements The authors are grateful to the Director, Central Soil and Water Conservation Research and Training Institute, Dehradun for providing financial and physical facilities for carrying out the present study. Thanks are also due to Mr. J.K. Maini and Mr. Ashok Kumar for their field work assistance and Mr. Deepak Kaul for cartographic work. Mr. S.N. Gupta, is also thankfully acknowledged for typing the manuscript.
References Aggarwal, P., Bhardwaj, S.P., Khullar, A.K., 1992. Appropriate tillage systems for rainfed wheat in Doon Valley. Ann. Agric. Res. 13, 116–173. Anonymous, 1977. Leucaena Promising Forage and Tree Crop for the Tropics. National Academy of Sciences, Washington, USA. Anonymous, 1985. Leucaena wood production and use. Nitrogen Fixing Tree Association ŽNFTA., P.O. 680, Waimanala, HI. Bhardwaj, S.P., Singh, P.N., 1981. Soils, land capability and land use characteristics of Soil Conservation Research Farm, Dehradun. Central Soil and Water Conservation Research and Training Institute, Dehradun, India, Bull. T-14rD-11. Bhushan, L.S., Ghosh, S., 1982. Effect of tillage and surface mulching on moisture conservation and yield of rainfed crops. Indian J. Soil Cons. 10, 97–100. Budelman, A., 1988. The performance of the leaf mulches of Leucaena leucocephala, Flemingia macrophylla and Glericidia sepium in weed control. Agroforestry Syst. 6, 137–145. Chaudhary, R.M., Prihar, S.S., 1974. Root development and growth response of corn following mulching, cultivation, or inter-row compaction. Agron. J. 66, 350–355. Daisley, L.E.A., Chong, S.K., Olsen, F.J., Singh, L., George, C., 1988. Effects of surface-applied grass mulch on soil water content and yield of cowpea and egg plant in Antigua. Trop. Agric. 65, 300–304. Doorenbos, J., Pruitt, W.O., 1977. Guidelines for predicting crop water requirements. FAO Irrig. Drain. Pap. 24 Žrev. 1977.. Food and Agriculture Organization, Rome, 156 pp. Gupta, S.N., 1991. Moisture use efficiency and root development of rape seed influenced by mulches under humid rainfed conditions. Indian J. Soil Cons. 19, 14–21. Hussain, A., Hussain, A., Chughtai, F.A., Zabair, M., 1988. L. leucocephala prunings as a source of nitrogen for wheat. Leucaena Research Report 9, pp. 84–95. A publication of the nitrogen fixing tree association ŽXIFTA., P.O. 680, Waimanalo, HI 96795, USA. Jackson, M.L., 1967. Soil Chemical Analysis. New Delhi, Prentice-Hall of India. Krishnamurthy, K., Mune Gowda, M.K., 1982. SOOBABUL ŽChiguru. w Leucaena leucocephala ŽL.. de Witx —A multi-purpose plant. University of Agriculture Sciences, Bangalore, USA, Tech. Series No. 38 ŽRevised.. Lal, R., 1989. Agroforestry systems and soil surface management of a tropical alfisol: V. Water infiltrability, transmissivity and soil water sorptivity. Agroforestry Syst. 8, 217–238. Mittal, S.P., Grewal, S.S., Agnihotri, Y., Sud, A.D., 1992. Substitution of nitrogen requirement of maize through leaf biomass of Leucaena leucocephala: agronomic and economic considerations. Agroforestry Syst. 19, 207–210.
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Rajput, R.K., Singh, M., 1970. Efficiency of different mulches in conserving soil moisture in cotton. Indian J. Agron. 15, 41–45. Read, M.D., Kang, B.T., Wilson, G.F., 1985. Use of Leucaena leucocephala Žlamk.. de Wit leaves as a nitrogen source for crop production. Fertilizer Res. 8 Ž2., 107–116. Singh, G., Bhushan, L.S., 1978. Role of surface mulching on moisture conservation and yield of wheat crop under rainfed condition. Central Soil and Water Conservation Research and Training Institute, Dehradun, Annual Report, 1978. Singh, G., Singhal, A.K., Nambiar, K.K.M., 1967. Effect of mulching on moisture retention and yield of wheat under rainfed conditions. J. Soil Water Cons. Ind. 15, 102–107. Singh, G., Koranne, K.D., Bhushan, L.S., Sumer, C., Ghosh, S., 1981. Advances in rainfed farming. Central Soil and Water Conservation Research and Training Institute, Dehradun, India, Bull., R-10rD-8. Tomar, V.P.S., Narain, P., Dadhwal, K.S., 1992. Effect of perennial mulches on moisture conservation and soil-building properties through agroforestry. Agroforestry Syst. 19, 241–252. Viets, F.S. Jr., 1962. Fertilizers and efficient use of water. Adv. Agron. 14, 223–269.
Effect of leucaena mulch on soil-water use and wheat yield N.K. Sharma a
a,)
, P.N. Singh b, P.C. Tyagi a , S.C. Mohan
a
Central Soil and Water ConserÕation Research and Training Institute, Dehradun-248 195, India b Indian Institute of Sugarcane Research, Lucknow-226002, India Accepted 14 October 1997
Abstract A study was undertaken to assess the effects of levels and timings of incorporation of leucaena w Leucaena leucocephala ŽL.. de Witx leaf mulch on soil-water use and performance of wheat ŽTriticum aestiÕum L.. grown on Dhoolkot silty clay loam soil in submontane northwest India. Air-dried leucaena leaves were applied as a surface mulch, at the rate of 0 ŽNo mulch., 2, 4 and 6 t hay1 as main plot treatments and its timings of soil incorporation namely: immediately, 15, 30 and 45 days after harvest of maize crop as subplot treatments. Each treatment was replicated four times in a strip-plot design. The results revealed that more moisture was available in mulched surface soil Ž0–15 cm. at the time of wheat sowing. Application of mulch increased moisture extraction, water use efficiency ŽWUE., grain and straw yield of wheat crop. Incorporation of leaf mulch at 30 days after harvesting of maize crop conserved more moisture for wheat sowing. This study indicated that optimal mulch application rate was 2 t hay1 and time of incorporation was at 30 days after maize harvest. q 1998 Elsevier Science B.V. Keywords: Organic mulch; Soil-moisture conservation; Water use; Wheat yield
1. Introduction Wheat is one of the staple rainfed winter season Ž rabi . food crops of the northwest submontane region of India. Yield is generally low because of early recession of the monsoon, resulting in low residual soil moisture during October–November, coinciding with the time of seeding and germination of wheat crop ŽSingh et al., 1981.. Besides, )
Corresponding author.
0378-3774r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 3 7 7 4 Ž 9 7 . 0 0 0 4 7 - 4
192
N.K. Sharma et al.r Agricultural Water Management 35 (1998) 191–200
drought spells during the crop season also cause severe moisture stress in the soil profile, particularly at critical growth stages of the wheat crop. Consequently, there is need for conserving soil moisture to avert moisture deficit at the time of sowing and also during crop-growth period. Earlier research has revealed that use of organic mulch helps in improving crop production through moisture conservation. It has also been reported that the beneficial effect of organic mulches is mainly due to reduced evaporation ŽRajput and Singh, 1970; Singh and Bhushan, 1978; Bhushan and Ghosh, 1982; Aggarwal et al., 1992.. Incorporation of organic matter has been reported to augment water retention capacity by improving the structure and physical environment of soil ŽHussain et al., 1988; Tomar et al., 1992.. Leucaena leucocephala ŽL.. de Wit, having very high biomass production ŽAnonymous, 1977; Krishnamurthy and Mune Gowda, 1982. and fast decomposition characteristics ŽMittal et al., 1992., can be used effectively as organic mulch. Leucaena leaves may be applied in the field just after maize harvesting initially to conserve soil moisture for proper germination of the subsequent wheat crop and later incorporation in the soil at a suitable time to enhance the moisture retention capacity during crop-growth period. It is appropriate, therefore, to determine the optimum quantity of leucaena leaves required for mulching and optimum time for mulch incorporation so as to conserve and improve the soil moisture for wheat crop production. Accordingly, a systematic field study was carried out.
2. Materials and methods 2.1. Experimental site A field study was carried out for 3 years Ž1990–1991 to 1992–1993. at the Selakui Research Farm, Central Soil and Water Conservation Research and Training Institute, Dehradun, India. The soil of the experimental area belongs to the Dhoolkot series ŽBhardwaj and Singh, 1981.. Soil was analyzed using standard chemical procedures ŽJackson, 1967.. Mechanical analysis showed that the soil was silty clay loam type and contained 37% silt, 40% sand and 23% clay. Soil-moisture characteristics indicated a permanent wilting point at 11.4%, field capacity at 27% with an average bulk density of 1.44 g ccy1 of surface Ž0–15 cm. layer. Soil pH was 5.2 and it contained 0.59% organic carbon, 0.066% total nitrogen, 31 kg hay1 available phosphorus and 165 kg hay1 available potassium. 2.2. Water use and water use efficiency Soil moisture was determined gravimetrically, using a core sampler. Soil samples for moisture content determination were collected from each plot in all the replications up to the depth of 75 cm. Soil samples were taken from 0–15, 15–30, 30–45 and 45–75 cm
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soil depths for moisture determination. Soil samples for moisture content were taken at the time of sowing and harvesting of wheat crop for profile moisture extraction. Soil samples were also taken before each rainfall event to determine soil moisture deficit for calculating the effective rainfall. The water use by the crop was calculated by the following formula: Water Use Ž mm . s Soil moisture Ž mm . at the time of crop sowing ysoil moisture Ž mm . at the time of crop harvest q Effective rainfall Ž mm . . Here, water use is referred to as evapotranspiration ŽET.. Soil moisture retained within 0–75 cm soil profile, to be used by the crop, was taken as effective rainfall in calculating layer-wise water use during the crop-growing period. For this purpose, moisture data for each soil layer of root zone were used. To determine effective rainfall, the moisture deficit in different soil layers of root zone on the day of precipitation was calculated based on the moisture depletion for the preceding day. To calculate the moisture depletion, soil samples were taken before each rainfall event. Afterwards, the known amount of precipitation was distributed to meet the moisture deficit up to the field capacity level in different layers, while the excess was taken as deep percolation. Potential ET was estimated from meteorological data using modified Penman equation ŽDoorenbos and Pruitt, 1977.. Water use efficiency ŽWUE. of the crop was computed using the following equation ŽViets, 1962.: WUE s YrET where WUE s kg hay1 mm water used, Y s yield of total dry matter or grain Žkg hay1 ., ET s evapotranspiration Žmm., water expenses. 2.3. Field experimentation After taking a uniform maize crop every year in the rainy season Ž kharif ., mulching treatments were imposed soon after maize harvest by early October. The experiment was laid out in strip-plot design with three replications. The treatments consisted of four levels of mulch material Žair-dried leucaena leaves., viz., no mulch Ž M0 ., 2 Ž M1 ., 4 Ž M2 . and 6 Ž M3 . t hay1 as main treatments and four timings of incorporation of the mulch material as subtreatments, viz., 0 Žimmediately after harvest, T1 ., 15 ŽT2 ., 30 ŽT3 . and 45 ŽT4 . days after maize harvest. The mulch was incorporated evenly in the soil of the experimental plot with the bullock drawn mould board plough. Wheat was seeded with seed drill every year by the third week of November in rows 22.5 cm apart. Nitrogen, phosphorus and potash were applied to wheat in the form of chemical fertilizers at the rate of 60, 40, 20 kg hay1 , respectively. Evaporation was measured on standard USWB open pan class A. Data on rainfall and evaporation ŽTable 1. corre-
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Table 1 Rainfall and evaporation for experimental period Period
Rainfall Žmm.
Evaporation Žmm.
1990–1991 1991–1992 1992–1993 1990–1991 1991–1992 1992–1993 Maize growing 1209.5 935.2 Mulch 146.0 12.1 Wheat growing 274.9 166.7 Up to 30 DAS of wheat crop 137.0 Ž50. 0.0 Ž0.
1042.8 21.0 195.0 12.4 Ž6.
449.4 143.7 362.1 45.6 Ž13.
434.2 137.9 373.4 41.2 Ž11.
458.8 136.0 366.0 49.1 Ž13.
Figures in parenthesis are percentages of total crop-growth period. DASsdays after sowing.
sponding to the period of experimentation in each year were taken from the meteorological observatory of the Research Farm.
3. Results and discussion 3.1. Soil moisture at sowing time Data on soil moisture as affected by mulch level and incorporation timings, are presented in Fig. 1. It was found that by mulching, more moisture was available in the upper soil layer Ž0–15 cm. for wheat sowing. Similar results were reported by Singh et al. Ž1967. and Singh and Bhushan Ž1978.. The highest percentage of moisture Ž13%. was conserved when the soil surface was kept covered with mulch up to 30 days after maize harvest, whereas the lowest Ž11.5%. was conserved when mulch was incorporated into soil soon after maize harvest. This may be due to variation in period of mulch coverage over soil surface. Furthermore, lower soil moisture was observed at the time of wheat sowing when mulch was incorporated after 45 days as compared to 30 days after maize harvesting. This is perhaps due to the fact that leucaena mulch loses its effectiveness, especially when the material is not wetted by rain ŽBudelman, 1988., and the half-life value of fresh leucaena pruning is not much longer than 3 weeks ŽRead et al., 1985..
Fig. 1. Surface soil moisture Ž0–15 cm. at wheat sowing as influenced by mulch levels and timings of incorporation. M0 s 0 t hay1 ; M1 s 2 t hay1 ; M2 s 4 t hay1 ; M3 s6 t hay1 ; T1 s Immediate; T2 s15 days; T3 s 30 days; T4 s 45 days.
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Fig. 2. Mean soil water extraction pattern Žmm. under wheat as influenced by mulch levels: M0 s 0 t hay1 ; M1 s 2 t hay1 ; M2 s 4 t hay1 ; M3 s6 t hay1 .
3.2. Soil moisture extraction pattern Data relating to moisture extraction pattern of the soil profile Ž0–75 cm. for each mulch level Žmean values of four dates of application. are depicted in Fig. 2. It was revealed that in case of no mulch treatment, 57% of total extracted moisture was used from 0–30 cm soil layer by the wheat crop. However, the mulch levels of 2, 4 and 6 t hay1 increased soil moisture extraction by the wheat crop to the extent of 60, 61 and 63%, respectively. Thus, it may be inferred that even a low quantity of leucaena leaf mulch Ž2 t hay1 . may contribute towards increased soil moisture extraction from surface layer. It was also observed that the duration of spread of mulch prior to incorporation in soil induced better moisture storage during the relatively dry year Ž1991–1992. as compared to normal rainfall years Ž1990–1991 and 1992–1993.. 3.3. Water use and water use efficiency Data on actual ET requirements of crop and potential ET are given in Tables 2 and 3, respectively. It was found that water use was considerably influenced by seasonal rainfall and levels of mulch. In high rainfall year Ž1990–1991. with 275 mm of rainfall during the crop season, higher utilization of water was noticed compared to lesser rainfall years Ž1991–1992 and 1992–1993.. The potential ET was, however, not found to vary much over the three-year period. As evident from the average data in Table 3, the increasing trend of actual water use ŽET. and ratio of actual water use and potential ET ŽETrETp ., has been observed with the increase in mulch rate from 2 to 6 t hay1 . However, in the initial two years the mulch treatment did not exhibit any consistent trend in the water utilization. It might be due to the fact that the mulch effect was visible only after a few years which resulted in improvement of soil properties ŽLal, 1989.. A similar trend was observed in the case of WUE. It is evident from Table 2 that WUE was decreased due to higher utilization of water in high rainfall year Ž1990–1991., as compared to lesser rainfall years Ž1991–1992 and 1992–1993.. Significantly higher WUE was observed in mulched treatments as compared to no mulch treatment. Maximum WUE was observed with 6 t hay1 mulch level in all the years but statistically at par with that of 4 t hay1 mulch level.
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Grain yield Žkg ha y1 .
1990–1991 1991–1992 1992–1993 1990–1991 1991–1992 1992–1993 1990–1991 1991–1992 1992–1993 1990–1991 1991–1992 1992–1993
0 Ž M0. 2 Ž M 1. 4 Ž M2. 6 Ž M 3. LSD Ž P s 0.05 .
3059 3726 3871 4215 345
2421 2924 3063 3161 112
Evapotranspiration Žwater use . Žmm .
Water use efficiency Žkg ha y1 mm y1 . Rate of water use Žmm day y1 .
Mulch level Žt ha y1 .
2343 2972 3372 3495 151
329.1 360.8 358.9 367.9 23.7
244.3 248.4 246.9 250.7 66.7
241.0 242.4 259.5 265.7 20.7
9.30 10.33 10.79 11.46 1.02
9.91 11.77 12.41 12.61 0.51
9.72 12.26 12.99 13.15 0.62
2.19 2.40 2.39 2.45 0.01
1.60 1.63 1.62 1.65 0.01
1.60 1.61 1.72 1.76 0.01
Table 3 Relationship between actual evapotranspiration and potential evapotranspiration as influenced by different levels of mulch Treatment
1990–1991 ET
ETp
ETrETp
ET
ETp
ETrETp
ET
ETp
ETrETp
ET
ETp
ETrETp
0 2 4 6
329.1 360.8 358.9 367.9
410.5 410.5 410.5 410.5
0.801 0.879 0.874 0.896
244.3 248.4 246.9 250.7
421.6 421.6 421.6 421.6
0.579 0.589 0.586 0.595
241.0 242.4 259.5 265.7
442.5 442.5 442.5 442.5
0.545 0.548 0.586 0.600
271.5 283.9 288.4 294.8
424.9 424.9 424.9 424.9
0.639 0.668 0.679 0.694
Ž M0. Ž M 1. Ž M2. Ž M 3.
1991–1992
ET sevapotranspiration Žmm. Žactual water use.. ETp s potential evapotranspiration Žmm..
1992–1993
Average Ž1990–1991 to 1992–1993 .
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Table 2 Grain yield, water use, water use efficiency and rate of water use as influenced by mulch levels
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Fig. 3. Relationship between mean water use and grain yield of wheat in respect of different mulch levels: ŽObserved.. Ž(. No mulch, Ž Ø . Mulch 2 t hay1 , Ž`. Mulch 4 t hay1 , Ž^. Mulch 6 t hay1 . Regression analysis Ž(. No mulch Ž M0 . Y s1088.20q56.28xŽ R 2 s 0.58. ŽØ. Mulch @ 2 t hay1 Ž M1 . Y s1781.00q51.13xŽ R 2 s 0.68. Ž`. Mulch @ 4 t hay1 Ž M2 . Y s1761.70q58.00xŽ R 2 s 0.77. Ž^. Mulch @ 6 t hay1 Ž M3 . Y s1165.24q82.90xŽ R 2 s 0.83.
Response of wheat grain yield to water use was estimated through linear regression equations. These equations indicated that with the increase of mulch level, WUE increased as was evident from improvement of R 2 from 0.58 Ž M0 . to 0.83 Ž M3 .. Response surface curves, presented in Fig. 3 also indicated the efficacy of mulch levels. Thus, response surface curves with mulch are always above those without mulch treatment. This may be due to improvement in soil environment by use of organic mulches, which promoted root growth and eventually water absorption. This is in accordance with the findings of Chaudhary and Prihar Ž1974. and Gupta Ž1991.. 3.4. Yields Wheat grain and straw yields were significantly Ž P - 0.05. influenced by mulch levels and timings of incorporation of mulch. Highest mean grain yield Ž3623 kg hay1 . and straw yield Ž5560 kg hay1 . were recorded in the plots which received mulch level of 6 hay1 . On the other hand, lowest grain yield Ž2607 kg hay1 . and straw yield Ž4548 kg hay1 . were recorded in plots with no mulch. Yield comparison for individual years revealed that yields due to mulching were found significantly Ž P - 0.05. higher than the control during all the years. However, in the year 1990–1991 Ža high winter rainfall
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Table 4 Wheat yield as influenced by the mulch levels and days of incorporation Treatment
Grain yield Žkg hay1 .
Straw yield Žkg hay1 .
1990–1991 1991–1992 1992–1993 Mean 1990–1991 1991–1992 1992–1993 Mean Mulch leÕel (t ha y 1) 0 Ž M0 . 3059 2 Ž M1 . 3726 4 Ž M2 . 3871 6 Ž M3 . 4215 LSD Ž P s 0.05. 345
2421 2924 3063 3161 112
2343 2972 3372 3495 151
2607 3207 3435 3623 236
5638 6356 6423 6971 749
4156 4990 5096 4940 321
3852 4516 4622 4769 297
4548 5287 5380 5560 333
Days of incorporation after spread of mulch 0 a ŽT1 . 3703 2641 2911 15 ŽT2 . 3859 2900 3119 30 ŽT3 . 3626 2989 3078 45 ŽT4 . 3681 3038 3074 LSD Ž P s 0.05. NS 58 NS
3085 3292 3231 3297 NS
6245 6497 6289 6356 NS
4648 4671 4891 4981 NS
4540 4360 4417 4442 NS
5141 5176 5199 5259 NS
NSs Nonsignificant. a Immediate incorporation.
year., the yield differences due to mulch levels were found nonsignificant. During the year 1991–1992 Ža dry year., wheat grain yield achieved due to 4 t hay1 mulch, was significantly Ž P - 0.05. higher than the yield due to 2 t hay1 . Yield differences due to 4 t hay1 and 6 t hay1 mulch levels were observed nonsignificant. Similar yield trend was observed in the crop year 1992–1993 with moderate rainfall. Nonsignificant differences in mean grain and straw yields were recorded due to different levels of mulch which has shown the importance of mere coverage of soil surface that reduced the evaporation from the soil surface. Similar results were obtained with cowpea and eggplant ŽDaisley et al., 1988.. Similarly for maize crop, about 3 t hay1 of fresh leaves of leucaena were recommended as an organic manure for optimum production ŽAnonymous, 1985.. Effect of mulch incorporation timings on the yield was influenced by the seasonal rainfall. Significant differences in yield were observed ŽTable 4. only in low rainfall year Ž1991–1992. as compared to 1990–1991 and 1992–1993. Amount of seasonal rainfall particularly within 30 days after sowing of wheat crop also influenced the wheat yield. It is inferred from the above discussion that in order to maximize the wheat production, mulching of dry leucaena leaves at the rate of 2 t hay1 appears quite adequate.
4. Conclusions The study indicates that leucaena which is a promising source of leaf biomass having high nutritive value can be used effectively as organic mulch in rainfed agriculture. Data from the study suggest that by applying leucaena leaves as a mulch, soil moisture losses due to evaporation can be reduced which ensure the availability of moisture for wheat germination and subsequent crop growth. In order to obtain maximum WUE, and grain
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and straw yield of wheat, soil surface should be covered uniformly with leucaena leaf mulch at the rate of 2 t hay1 immediately after maize harvest and should be incorporated into the soil after allowing it to remain at the soil surface for 30 days. The findings of the study are promising to improve and stabilize the production of rainfed wheat.
Acknowledgements The authors are grateful to the Director, Central Soil and Water Conservation Research and Training Institute, Dehradun for providing financial and physical facilities for carrying out the present study. Thanks are also due to Mr. J.K. Maini and Mr. Ashok Kumar for their field work assistance and Mr. Deepak Kaul for cartographic work. Mr. S.N. Gupta, is also thankfully acknowledged for typing the manuscript.
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