Scientific registration n o : 217 Symposium n o : 40 Presentation : poster BIJAY-SINGH, YADVINDER-SINGH, KHIND C.S.

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1 Scientific registration n o : 217 Symposium n o : 40 Presentation : poster Managing organic manures and mineral fertilizers for maintaining soil organic matter and sustainable yields of rice and wheat in the Indo-Gangetic plains of South Asia Gestion des fumures organiques et minérales en vue de maintenir le stock de matière organique et les rendements du blé et du riz dans la plaine du Gange en Inde BIJAY-SINGH, YADVINDER-SINGH, KHIND C.S. Department of Soils, Punjab Agricultural University, Ludhiana , India Introduction In the Indo-Gangetic plains in South Asia, area under sequentially grown crops of rice and wheat in an annual rotation extends to more than 12 million ha (Huke and Huke, 1992). 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 the eighties, the system is showing signs of fatigue and is no longer exhibiting increased production with increases in input use. In this context, soil organic matter depletion in rice-wheat system is a matter of great concern although several complex interactions between management of rice and wheat are involved. In cultivated soils, cropping system and associated cultural practices influence the level at which organic matter will stabilize. When manures and fertilizers are applied to the soil to maintain efficient plant cover, decline in organic matter is arrested and this in turn leads to sustainable crop yields. Long-term experiments conducted in India have shown that integrated use of organic manures including green manure and chemical fertilizers can maintain high productivity and provide sustained stability in crop production. This paper addresses to the issue of organic matter in rice-wheat system in terms of achieving sustainable production from this cropping system in the Indo- Gangetic plains in South Asia. Organic matter status of the soil In 1971, long-term field experiments on rice-wheat rotation were initiated at Barrackpore in West Bengal and Pantnagar in Uttar Pradesh. After 16 years of sequentially growing rice and wheat with recommended dose of NPK fertilizers, organic 1

2 carbon content of the soil was less by 30 and 38 % than the values at the start of the experiment at Barrackpore and Pantnagar, respectively (Table 1). In contrast, in all other systems, organic carbon appreciated with the balanced use of NPK fertilizers. Data from two maize-wheat systems and a rice-rice system are shown in Table 1. Initial soil organic carbon level was maintained at Pantnagar by combined application of NPK fertilizers and farmyard manure (FYM) but at Barrackpore loss of organic matter was still more than 13%. It seems that frequent tillage and Table 1. Changes in organic carbon content (g/kg) of the soils under different cropping systems as influenced by fertilizer and farmyard manure (FYM) treatments during (Adapted from Nambiar et al. 1989) Treatment Rice-wheat -jute Maize-wheatcowpea Rice-rice Rice-wheat- Maize-wheat (fodder) cowpea (fodder) 50% NPK % NPK % NPK % NPK FYM Control Initial status Soil group/ Recent alluvium Alluvial Lateritic Foot hill Submontane association Texture Sandy loam Loamy sand Sandy loam Silty clay loam Silt loam Location Barrackpore Ludhiana Bhubaneswar Pantnagar Palampur alternating wetland (rice) and upland (wheat) conditions lead to rapid decomposition of soil organic matter in rice-wheat system. Verma et al. (1987) have reported a 16.7% loss of initially present organic carbon in control plots after seven cycles of rice-wheat rotation at Masodha. Depletion of organic carbon was only 2% when 120 kg N + 26 kg P + 33 kg K/ha was applied to rice as well as wheat. Application of FYM or compost is the best in maintaining soil organic matter in Indian soils (Gaur et al., 1984). The next in the order is cereal straw/residues. At the end of 5 cycles of rice-wheat rotation in a Typic ustipsamment at Ludhiana in Punjab, there was a conspicuous increase in the organic carbon content of the soil in the FYM amended plots (3.3 g/kg) as compared with levels in unamended (2.4 g/kg) plots or at the initiation of the experiment (2.2 g/kg) (Maskina et al. 1988). Due to their succulent nature, narrow C:N ratio and low lignin content, green manures decompose rapidly when incorporated into soil (Yadvinder Singh et al., 1992) and only a small quantity of carbon is converted into stable soil humus. Boparai et al. (1992) observed that while organic carbon content of the unamended soil under ricewheat rotation decreased from 1.9 g/kg to g/kg after three years, green manuring helped to maintain it at the initial level. Bhardwaj et al. (1981) and Sharma and Mittra (1988) observed increase in the soil organic carbon content ranging from 0.4 to 1.0 g/kg due to green manuring of rice in rice-wheat system. 2

3 Organic amendments and yield sustainability The almost universal loss of organic matter from intensively cultivated soils is central to the issue of agricultural sustainability. In a large number of experiments conducted in the Indo-Gangetic plains, effect of applying FYM to rice, wheat or both was studied on the yield of rice and wheat each grown with 100 kg N/ha (Table 2). In general, yield increases were more when FYM was applied to both the crops rather than to rice or wheat suggesting a positive role of FYM in achieving yield sustainability in rice-wheat system in India. Under sub temperate humid climate at Palampur, Sharma et al. (1987) observed that after four crop seasons soil organic carbon content was 8.7, 11.7, 12.9 and 16.0 g/kg depending upon whether FYM was not applied, applied to rice, to wheat or to both the crops, respectively. The yield response to FYM application followed the pattern of organic carbon in the soil. It is surmised that FYM plays an additional role than its capacity to contribute NPK. It is well known for improvement in soil physical environment. The long-term fertilizer experiments conducted in India during have shown that neither organic manures nor NPK fertilizers alone can achieve yield sustainability at a high level under modern intensive farming (Nambiar and Abrol, 1989). The yield data from long-term experiments initiated in 1971 (Table 3) demonstrate the superiority of integrated use of organic manures and chemical fertilizers in providing greater stability in crop production in rice-wheat system at Pantnagar and in rice-rice or maize-wheat systems at different locations, when compared with chemical fertilizers alone (150% NPK) supplying more NPK than the former. At Barrackpore, however, the 150% NPK treatment yielded more rice and wheat than 100% 3

4 Table 2. Direct, residual and cumulative responses of average yield (t/ha) to farmyard manure at 15t/ha in rice-wheat rotation in Uttar Pradesh, Madhya Pradesh and West Bengal in India during 1969 to (Adapted from Gaur et al. 1984) Location Farmyard manure applied to Control Response Control Response Control Response Uttar Pradesh Varanasi Rice Wheat Bichpuri Rice Wheat Masodha Rice Wheat , Pura farm Rice Wheat Madhya Pradesh Rice Wheat Rice Wheat Rice Wheat West Bengal Kharagpur Rice Wheat NPK + FYM, inspite of the fact that FYM checked the loss of soil organic matter. It seems that declining soil organic matter is not the only cause of not achieving yield sustainability; rather large nutrient removals can cause a drain on the soil fertility and the soil may not be able to sustain high productivity in the future. During five years of following rice-wheat rotation at Ludhiana, Maskina et al. (1988) could not increase yield levels by applying FYM + N 80 more than N 120 alone, although a significant build up of organic carbon content from 2.2 g/kg to 3.3 g/kg was observed. In a 3-year on farm study carried out at locations in Uttar Pradesh in India, supplying 20% of the N requirement of the rice-wheat rotation with FYM not only resulted in sustainable high yields but also an average increase in soil organic carbon levels from 3.7 to 6.3 g/kg (Thakur et al. 1997). Under rice-wheat system in Pakistan, Ahmed and Hamid (1997) observed that meeting 20% of the N requirement of the rotation with FYM or organic sources can ensure sustainable high yields. 4

5 Table 3. Effect of chemical fertilizers applied alone or along with farmyard manure (FYM) on yield of crops in rice-wheat vis-a-vis other systems in long-term experiments (Adapted from Nambiar et al., 1989) Soil group/ Crop Mean grain yield (t/ha) Mean grain yield (t/ha) Location during during % 150% 100% 100% 150% 100% NPK NPK NPK+ FYM NPK NPK NPK+FYM Recent Alluvium, Rice Barrackpore Wheat Alluvial, Maize Ludhiana Wheat Laterite, Rice Bhubaneswar Rice Foothill, Rice Pantnagar Wheat Submontane, Maize Palampur Wheat Crop residue management in rice-wheat system Overcoming soil organic matter decline is an important component in the developemnt of more sustainable agroecosystems.yet in many tropical cropping systems, little or no agricultural residues are returned to the soil. This leads to a decline in soil organic matter which frequently results in lower crop yields. Traditionally, wheat and rice straw have been removed from the fields in the Indo-Gangetic plains in South Asia; wheat straw is used for feeding the animals whereas rice straw is removed because it adversely affects the yield of the following wheat. Possibly it is one of the important causes for organic matter depletion in rice-wheat system. Recently, due to the advent of mechanized harvesting, large quantities of crop residues left in the field are burnt in situ by the farmers and this practice has important implications on the organic matter content of the soil. Data listed in Table 4 reveal that there is significant build up of soil organic matter due to incorporation of straw of rice and wheat into the soil as compared to when these are removed or burnt. However, yield of rice and wheat show a trend opposite to that of organic matter build up. In residue incorporated treatments, yields were low due to immobilization of soil and fertilizer N by decomposing crop residues with wide C:N ratio (Yadvinder Singh et al., 1988). Nevertheless, in these studies there was a significant improvement in the soil physical environment due to build up of organic matter by crop residue incorporation. In a long-term experiment progressing at Ludhiana (Punjab), it has been revealed that adverse effects of wheat or rice straw residues can be effectively counteracted by 5

6 combined incorporation of green manure (narrow C:N ratio) and crop residues (wide C:N ratio) into the Table 4. Effect of crop residue management on soil organic matter content and grain yield of the crops in rice-wheat rotation in India Reference Duration Residue Organic Mean grain yield of crop (t/ha) of study management carbon Rice Wheat (Years) (g/kg) Beri et al. (1995 ) 10 Removal Burnt Incorporated Sharma et al. (1987) 6 Removal * 2.65 Incorporated * 2.73 Dhillon and Dev (1984) 2 Removal Burnt Incorporated * Direct seeded upland irrigated rice soil before transplanting of rice). The superiority of this practice over applying crop residues or green manure alone is that besides high yields, there is a significant build up of organic matter in the soil which helps to attain sustainable crop production in the ricewheat system. Green manuring of rice is well known for its role in supplying N (Yadvinder Singh et al., 1991). References Ahmad N. And Abdul H Integrated plant nutrition system (IPNS) : Research and development in Pakistan. Proceedings of the FAO-IFFCO Internationa; Seminar on IPNS for Sustainable Development. Indian Farmers Fertiliser Cooperative Limited, New Delhi. Beri, V., Sidhu, B.S., Bahl, G.S. and Bhat, A.K Nitrogen and phosphorus transformations as affected by crop residue management practices and their influence on crop yield. Soil Use and management 11: Bhardwaj, S.P., Prasad, S.N. and Singh, G Economizing nitrogen by green manures in rice-wheat rotation. Indian Journal of Agricultural Sciences, 51, Boparai, B.S., Yadvinder-Singh and Sharma, B.D Effect of green manuring with Sesbania aculeata on physical properties of soil and on growth of wheat in rice-wheat and maize-wheat cropping systems in a semi arid region of India. Arid Soil Research and Rehabilation, 6, Dhillon, N.S. and Dev, G Effect of using fertilizer N and P with straw management practices in rice-wheat rotation. Bulletin of the Indian Society of Soil Science, 13,

7 Gaur, A.L., Neelakantan, S. and Dargan, K.S Organic Manures. New Delhi, Indian Council of Agricultural Research, 159 p. Huke, R. and Huke, E Rice/wheat Atlas of South Asia, IRRI, CIMMYT and NARS, 50 p. Maskina M.S., Bijay-Singh, Yadvinder-Singh, Baddesha, H.S.and Meelu, O.P Fertilizer requirement of rice-wheat and maize-wheat rotations on coarse textured soils amended with farmyard manure. Fertilizer Research, 17, Nambiar, K.K.M. and Abrol, I.P Long-term fertilizer experiments in India-An overview. Fertiliser News, 34(4), Nambiar, K.K.M., Soni, P.N., Vats, M.R., Sehgal, D.K. and Mehta, D.K Annual Report / , All India Coordinated Research Project on Long Term Fertilizer Experiments. New Delhi, Indian Council of Agricultural Research, 50 p. Sharma, A.R. and Mittra, B.N Effect of green manuring and mineral fertilizers on growth and yield of crops in rice based cropping on a laterite soil. Journal of Agricultural Sciences, Cambridge, 110, Sharma, H.L., Singh, C.M. and Modgal, S.C Use of organics in rice-wheat crop sequence. Indian Journal of Agricultural Sciences, 57, Thakur, M.S., Mishra, P.C., Pandey, D.K., Sharma, A.K. and Pandey G.K Integrated nutrient management for rice-wheat system. Proceedings of thenational workshop on IPNS. Indian Farmers Fertiliser Cooperative Limited, New Delhi, pp Verma, L.P., Yadav, D.S. and Room Singh Effect of continuous cropping and fertilizer application on fertility status of soil. Journal of the Indian Society of Soil Science, 35, Yadvinder-Singh, Bijay-Singh and Khind, C.S Nutrient transformations in soils amended with green manures. Advances in Soil Science, 20, Yadvinder-Singh, Bijay-Singh, Maskina, M.S. and Meelu, O.P Effect of organic manures, crop residues and green manure (Sesbania aculeata) on nitrogen and phosphorus transformations in a sandy loam at field capacity and waterlogged conditions. Biology and Fertility of Soils, 6, Yadvinder-Singh, Khind, C.S. and Bijay-Singh Efficient management of leguminous green manures in wetland rice. Advances in Agronomy, 45, Keywords: organic matter, rice, wheat, fertilizer, organic manures, crop residues, compost Mots clés : matière organique, riz, blé, engrais, fumure organique, résidu de culture, compost 7