Scientific registration n : 178 Symposium n : 40 Presentation : poster YADVINDER-SINGH, BIJAY-SINGH, KHERA T.S., KHIND C.S.

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1 Scientific registration n : 178 Symposium n : 40 Presentation : poster Crop residue management for improved soil and crop productivity in rice-wheat cropping system in Indo- Gangetic plains of India Gestion des résidus de récolte pour augmenter la productivité des sols et des cultures dans les rotations rizblé dans la vallée du Gange en Inde YADVINDER-SINGH, BIJAY-SINGH, KHERA T.S., KHIND C.S. Department of Soils, Punjab Agricultural University, Ludhiana , India ABSTRACT Laboratory and field experiments were conducted to study the long-term effects of green manure and crop residues on crop yields and soil productivity in rice-wheat cropping system. In laboratory incubation studies large amount of N was immobilized with the application of rice and wheat straw. Nitrogen immobilization was lower with rice straw than with wheat straw. Under optimum temperature and moisture conditions remineralization of immobilized N started 6 weeks after incubation. In a long-term study, incorporation of 52- day-old Sesbania aculeata green manure along with crop residues not only counteracted the adverse effects of crop residues but also improved soil health. In a 4-year study, in-situ incorporation of rice straw for 20 to 40 days before sowing of wheat showed no adverse effect on wheat yield. Application of 25% N at the time of incorporation of rice straw and inoculation with cellulytic microbes did not improve grain yield of wheat. Long-term application of crop residues significantly increased the organic carbon, and total as well as available N, P and K contents of soil. Incorporation of green manure and crop residues improved soil aggregation, reduced soil bulk density and increased infiltration rate of soil. INTRODUCTION The rice-wheat system extends to more than 10 million ha in Indo-Gangetic plains of India. During 1960 to 1990, genetic improvements in rice and wheat and improved management strategies resulted in a rapid increase in area under this system. After a dramatic rise in productivity and production during 1980's, the system is showing signs of fatigue and is no longer exhibiting increased production with increase in input use. Declining area under legumes and green manures, less availability of organic manures and burning of 1

2 crop residues are responsible for making rice-wheat production system unsustainable. In the coming decades, a major issue in designing sustainable agricultural systems will be the management of soil organic matter and the rational use of organic inputs such as animal manures, industrial wastes, green manure and crop residues. Farmyard manure is the most commonly used organic manure, but it is limited in supply and contains low and variable nutrient contents. Green manures offer considerable potential as a source of plant nutrients and organic matter (Yadvinder-Singh et al., 1991). A considerable area under rice and wheat in Indian Punjab is now harvested by combine. The rice and wheat straws left in the field after combine harvesting are generally burnt by the farmers to facilitate seed bed preparation and seeding. Crop residues contain large quantities of nutrients accumulated by rice and wheat crops. Burning causes loss of organic matter and plant nutrients, and environmental pollution. Incorporation of cereal straws of wide C:N ratio, however, is reported to immobilize soil N and adversely affects the yield of the succeeding crop (Sidhu & Beri, 1989). Recycling of crop residues without adversely affecting crop yields has been attracting the attention of soil scientists. Laboratory and field experiments were conducted to study the long-term effects of green manure and crop residues on crop yields and soil productivity in rice-wheat cropping system. MATERIALS AND METHODS Field Experiments A long-term field experiment with a rice-wheat rotation was initiated in summer 1988 at the farm of Punjab Agricultural University, Ludhiana (30 o 56'N, 75 o 52'E), Punjab, India. The soil of the experimental field was Fatehpur loamy sand (Typic Ustipsamment) and had ph 7.6 and organic carbon 0.36%. The experiment with 6 treatments (Table 2) was laid out in a randomized complete block design with three replications. Total dry biomass and N added through green manure (GM) ranged from 2.3 to 4.8 t ha -1 and 60 to 130 kg N ha -1, respectively. Nitrogen added through GM in different years was supplemented with urea-n to give a total of 150 kg ha -1 for comparison with 150 kg N h -1 on unamended plot. Fifty to fifty-five-day old sesbania was incorporated into the soil with the help of a tractor-drawn disc harrow 1-2 days before transplanting rice. In the unamended, urea was applied in three equal split doses at transplanting, and 21 and 42 days after transplanting of rice. In the green manured plots, urea was applied in two equal doses at 21 and 42 days after transplanting. No P and K fertilizers were applied to rice. After rice harvest wheat was sown in the first week of November. A basal dose of 90 Kg N as urea+ 26 Kg P as superphosphate + 50 kg K as muriate of potash ha -1 was applied to wheat. Another long-term field experiment was initiated in summer 1993 to study the efficient management of rice straw in the following wheat in rice-wheat cropping system. Randomized complete block design with seven treatments (Table 3) and three replications was used. After combine harvesting of rice in the last week of September, rice was either removed from the plots or incorporated in situ with disc plough. Half of the N to wheat was applied and incorporated into the soil surface at sowing and the remaining half was applied as top dressed at the time of first irrigation. In one of the treatments 25% of the N 2

3 was applied at the time of incorporation of crop residues. Wheat was planted in the second week of November. After the wheat harvest in the second week of April, rice was transplanted as a residual crop which received a uniform dose of 120 kg N ha -1. Laboratory incubation experiment: Nitrogen mineralization-immobilization in the soil amended with rice and wheat straw was studied in laboratory at field capacity moisture regime in a loamy sand soil incubated at 15 and 35 o C. The soil was taken from the site of the first field experiment. Portions of soil samples weighing 500 g (oven dry basis) were place in 1l plastic containers and the crop residues were mixed into the 0.3%. Total N content in rice straw was 0.75% (C:N ratio=61.4) and in wheat straw was 0.40% (C:N ratio=122.4). Soil samples were removed after 1, 7, 14, 28, 56 and 84 days after incubation. These were extracted with 2M KCl solution immediately after sampling to estimate ammonium and nitrate-n. RESULTS AND DISCUSSION N mineralization-immobilization studies in laboratory: Incorporation of rice and wheat straw caused significant immobilization of mineral N in soil at both 15 and 35 o C (Table 1). The rate of immobilization of N in soil was considerably higher at 35 than at 15 o C. Addition of crop residues at 35 o C reduced the mineral N content from 27.5 mg kg -1 under unamended soil to 2.7 mg kg -1 soil within 7 days of incubation. The drop in mineral N at 15 o C was gradual and extended over a period of 56 days. Yadvinder-Singh et al. (1988) observed large amount of N immobilization from soil Table 1: Effect of crop residues on kinetics of N-mineralization in a loamy sand soil during aerobic incubations at 15 o and 35 o C Treatment Mineral-N (mg kg- 1 )on days of incubation A. 15 o C Control Rice straw Wheat straw B. 35 o C Control Rice straw Wheat straw

4 and applied N in the soil amended with rice and wheat straw at 35 o C. Nitrogen immobiliztion occurred at a lower rate with rice straw than that with wheat straw. Remineralization of immobilized N started at 56 and 28 days after incubation at 15 and 35 o C, respectively. These results bring out that adverse effect of N immobilization due to incorporation of crop residues on crop growth is likely to be greater during summer (rice season) than during winter (wheat season). Management of wheat straw and green manure in rice Crop Yields: Grain yield of rice increased significantly with 150 kg N ha -1 relative to unamended no-n control every year (Table 2). The yield increases with the application of 150 kg N ha -1 over the no-n control ranged from 1.2 to 2.6 t ha -1 (mean 2.08 t ha -1 ). Bijay- Singh et al. (1987) obtained significant response of rice to N application up to 150 kg N ha -1 in soils low in organic carbon. Green manure-n (GM-N) supplemented with fertilizer N to provide a total of 150 kg N ha -1 produced rice grain yields similar to those obtained from the application of 150 kg N ha -1 as urea. These data suggest that GM-N was about as efficient as fertilizer N in rice. Yadvinder-Singh et al. (1990) have reported equal or higher efficiency of GM-N compared with fertilizer N on rice. This is explicable from a laboratory incubation study showing rapid mineralization of GM-N under waterlogged conditions representing the rice ecosystem (Yadvinder-Singh et al., 1988). The wheat straw plus 150 kg urea-n ha -1 treatment, compared with 150 kg urea-n ha -1 alone, resulted in reduced rice grain yield in 5 out of 7 years. Laboratory incubation studies showed distinct evidence of N immobilization in straw amended soil at 35 o C. Sidhu & Beri (1989) have also reported a reduction in rice yield with incorporation of wheat straw into the soil. The adverse effect of wheat straw incorporation on rice grain yield was not observed when sesbania GM was grown and incorporated before transplanting rice (Table 2). Similar yields were also obtained with the rice straw + GM treatment. Table 2. Effect of green manure and crop residue management on rice grain yield,t ha - 1 Treatment No-N control kg N ha Green manure(gm) Wheat straw+gm Rice straw+gm Wheat straw kg N ha -1 LSD (P = 0.05)

5 The residual effects of different treatments applied to rice was not generally reflected in grain yield of wheat which received uniform dose of 90 kg N ha kg P ha kg K ha -1. The legume GM with narrow C:N ratio decomposed fast during rice growing season and did not increase organic carbon content of the soil, thereby showing no significant residual effect on wheat yield. Wheat/rice straw with wide C:N ratios applied alone or in combination with GM increased the organic C content of soil, but did not release enough N to increase wheat yield. Low or no residual effect of GM applied to rice on the succeeding wheat crop of wheat have been frequently reported in literature (Meelu et al., 1994). Nitrogen Uptake: Total N uptake by rice increased significantly with application of 150 kg N ha -1 over no-n control. Like rice grain yield, total N uptake under GM and rice/wheat straw plus GM treatments was equal or higher than with the 150 kg fertilizer N ha -1 treatment. Immobilization of fertilizer N in wheat straw+ 150 kg N ha -1 treatment was clearly reflected in reduced N uptake in all the years. Apparent urea-n recovery by rice ranged from 30.7 to 56.0 per cent with a mean value of 43.5 per cent. Soil Nutrient Status: Green manuring, as compared to fertilizer N, did not significantly increase organic carbon content of soil. Leguminous GM decomposed fast on incorporation into the soil under the experimental conditions characterized by high temperature and alternate aerobic - anaerobic conditions (Yadvinder -Singh et al., 1992). Therefore, only a small fraction of GM carbon was converted into stable soil humus. Incorporation of crop residues alone or in combination with GM significantly increased the soil organic carbon content. Beri et al. (1992) have reported that crop residue incorporation, as compared to its removal, markedly increased organic carbon and total N contents in soil under rice-wheat cropping system. Available P and K contents in soil decreased with the application of 150 kg N ha -1 and GM over no-n control. Total P and K removals by rice were higher under these treatments than under control. Also, total P and K inputs in the rice-wheat cropping system were much lower than that of removals by the crops resulting in negative P and K balances during the study. Therefore, the effect of GM and crop residues on available P and K contents of soil was perhaps not reflected over long-term period. However, green manuring may have increased the availability of P in soil over short term basis during the rice growth as reported in a laboratory incubation study by Yadvinder-Singh et al. (1988). Although significant quantities of total K were added through crop residues, small effect on available K content of soil was observed. This may also be due to the fixation of K released from crop residues into non-exchangeable forms and also leaching of water soluble K in the highly percolating coarse textured soil used in the study. Soil physical properties: Incorporation of GM, wheat straw, wheat straw + GM increased the formation of water stable aggregates particularly > 2mm size over fertilizer N treatment. Mean weight diameter of water stable aggregates was maximum in the treatment receiving combined application of GM. improvements in soil structure in terms of aggregation from GM and wheat straw incorporation have already been reported in literature (Boparai et al. 5

6 1992).The intake rate of water under GM and wheat straw treatments was greater than the fertilizer N alone treatment. Combined application of GM and straw effected a greater increase in the water intake rate compared to their separate application.. Increases in soil infiltration and hydraulic conductivity when aggregate stability was improved have been reported by Sharma et al. (1987). Management of rice straw in wheat Grain yield of wheat increased significantly with 120 kg N ha -1 relative to unamended no-n control every year (Table 3). The yield increase with the application of 120 kg N ha -1 ranged from 2.24 to 2.67 t ha -1. Incorporation of rice straw into the soil and allowing its decomposition for 40 days as compared with no residue treatment, showed no adverse effect on the grain yield of wheat except during the first year of study. Spraying of cellulytic microbial culture to enhance the decomposition of rice straw showed no beneficial effect on grain yield of wheat. When the decomposition period of rice straw was reduced from 40 to 20 days no harmful effect of rice straw on wheat yield was observed (Table 3). Application of a part of N (30 kg N ha -1 ) at the time of straw incorporation to enhance its decomposition showed no advantage over the recommended method of N application. The results of the laboratory incubation study corroborates the findings from field study that N immobilization effect of rice straw will relatively be small adversely effect the yield of wheat crop. Incorporation of rice straw significantly increased the soil organic C and available K contents of the soil. The grain yield of following rice was not significantly affected by the incorporation of rice straw in the preceding wheat crop. Table 3 Effect of N application and rice straw management on wheat grain yield (t/ha) Treatment No-N Control kg N ha Rice straw(40days DP * )+N Rice straw(40days DP) +N Rice straw(40days DP) CM ** + N 120 Rice straw(20days DP * )+ N Rice straw(20days DP * ) N 120 (25% N at incorporation of rice straw) LSD(0.05) * decomposition period, ** cullulytic microbes 6

7 References Beri, V., Sidhu, B.S., Bhat, A.K. & Bhupinder Pal Singh Nutrient balance and soil properties as affected by management of crop residues. In: Proceedings of the International symposium on Nutrient Management for Sustained Productivity, Vol. II. (eds. V. Beri, M.R. Chaudhary, P.S. Sidhu, N.S. Pasricha and M.S. Bajwa). Department of Soils, Punjab Agricultural University, Ludhiana, India. pp Bijay-Singh, Yadvinder-Singh & Maskina, M.S Rice response to higher N-application in soil testing low in organic carbon. Progressive Farming (PAU) 23(9), 13. Boparai, B.S., Yadvinder-Singh & Sharma, B.D Effect of green manuring with Sesbania aculeata on physical properties of soil and growth of wheat in rice-wheat and maize-wheat cropping system in a semiarid region of India. Arid Soil Research and Rehabilitation 6, Meelu, O.P., Yadvinder-Singh & Bijay-Singh Green Manuring for Soil Productivity Improvement. FAO World Soil Resources Reports No.76. FAO, Rome, Italy. Sharma, H.L., Singh, C.M. & Modgal, S.C Use of organics in rice-wheat crop sequence. Indian Journal of Agriculture Science 57, Sidhu, B.S. & Beri, V Effect of crop residue management on the yields of different crops and on soil properties. Biological Wastes 27, Yadvinder-Singh, Bijay-Singh, Maskina, M.S. & Meelu, O.P Effect of organic manures, crop residues and green manures (Sesbania aculeata) on nitrogen and phosphorus transformations in a sandy loam at field capacity and under waterlogged conditions. Biology and Fertility of Soils 6, Yadvinder-Singh, Bijay-Singh, Meelu, O.P. & Maskina, M.S Nitrogen equivalence of green manure for wetland rice on coarse textured soils. International Rice Research Newsletter 15(1), 23. Yadvinder-Singh, Bijay-Singh & Khind, C.S Nutrient transformations in soils amended with green manure. Advances in Soil Science 20, Yadvinder-Singh, Khind, C.S. & Bijay-Singh Efficient management of leguminous green manures in wetland rice. Advances in Agronomy 45, Keywords: crop residues, rice, wheat, green manure, nitrogen, mineralization, immobilization Mots clés : résidu de culture, riz, blé, engrais vert, azote, minéralisation, immobilisation 7