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Demand for crop residue for cooking fuel and animal feed is high in South Asia (Bronson et al., 1998). Re-Most double-crop grain farmers in South Asia remove or burn moval or burning of residue ensures farmers' quick seedcrop residue to facilitate seedbed preparation and to avoid possible yield reductions. This results in loss of soil organic matter (SOM) and bed preparation and avoids the risk of reduced crop nutrients. In this study, we determined whether incorporating wheat yields associated with incorporating wide C/N ratio resi-(Triticum aestivum L.) residue, rice (Oryza sativa L.) residue, and due that immobilizes N during decomposition (Khera, sesbania (Sesbania aculeta L.) green manure with urea fertilizer N 1993; Beri et al., 1995). The benefits of sequestering in a rice-wheat cropping system can improve grain yields, N use soil organic C (SOC) to sustaining crop productivity efficiency, and SOM. We incorporated wheat residue (6 Mg ha Ϫ1 , by applying organic amendments and crop residue and C/N ϭ 94), rice residue (6 Mg ha Ϫ1 , C/N ϭ 63), or both, with and including legumes in crop rotations have been well docuwithout green manure (20 or 40 Mg fresh ha Ϫ1 , C/N ϭ 19), in a field mented in the temperate regions. Although many green experiment with irrigated rice and wheat grown each year in rotation manuring studies have been conducted with rice in Asia on a Tolewal sandy loam (Typic Ustochrept) in the Punjab of India. (Buresh et al., 1993; Yadvinder-Singh et al., 1993), few Rice and wheat residue did not affect grain yields of wheat and rice, but residue incorporation did result in reduced recovery efficiency of studies have looked at comparative effects of crop resiurea N and green manure N. Rice production was greater with wheat due management with or without fertilizer N and leresidue incorporation when an average of 86 kg N ha Ϫ1 of a prescribed gume green manure on crop yields and SOC. 120 kg N ha Ϫ1 dose was applied as green manure N and the balance Annual rice-wheat double-crop systems occupy 21 as urea N vs. 120 kg urea N ha Ϫ1 alone. Despite wider C/N than rice million ha in the Indo-Gangetic plains of South Asia residue, wheat residue additions to flooded rice resulted in greater and China (Woodhead el al., 1994). On-station data C sequestration in soil than with rice residue or 40 Mg green manure from long-term experiments in China (Byerlee, 1992), ha Ϫ1 . These results demonstrate that a green manure crop and/or * Significant at the 0.05 probability level. ** Significant at the 0.01 probability level. † WR ϭ wheat residue (subscript is Mg ha Ϫ1 ); FN ϭ fertilizer N (subscript is kg ha Ϫ1 , X is varied); GM ϭ green manure (subscript is Mg ha Ϫ1 ). ‡ RR ϭ rice residue (subscript is Mg ha Ϫ1 ); FN ϭ fertilizer N (subscript is kg ha Ϫ1 ). § Values within this column followed by same letter do not differ significantly (P Ն 0.05) by Duncan's Multiple Range Test. ¶ Values within the next three columns followed by same letter do not differ significantly (P Ն 0.05) by Duncan's Multiple Range Test. # A...

nures and composts are in limited supply and may have low and variable nutrient contents. The more readily Integrating fertilizer N (FN) with legume green manures (GM) available green manures constitute a valuable source of can foster sustainable and environmentally sound agricultural systems both N and organic matter (Buresh and De Datta, 1991; in subtropical, semiarid soils low in organic matter. A 4-yr replicated field experiment with irrigated rice (Oryza sativa L.

Rice (Oryza sativa L.)–wheat (Triticum aestivum L.) farmers in India burn or remove residues to facilitate seedbed preparation. Incorporation of residues before planting of the next crop generally decreases yields due to N immobilization. Since a window of about 40 d is available between rice harvest and wheat planting, the effect of time of incorporation on rice residue decomposition and N mineralization–immobilization was studied in 1992–1993. The mass loss of residue was 25% for a 10‐d, 35% for a 20‐d, and 51% for a 40‐d decomposition period before wheat planting. Nitrogen release from residue ranged from 6 to 9 kg ha−1 during the wheat season. The immobilization of urea N decreased when residue was allowed to decompose for 10‐d or longer. Based on these studies, a long‐term (1993–2000) experiment was conducted on a sandy loam soil to examine the effect of time of residue incorporation before sowing wheat when compared with burning or removal of residue on yields, N‐use efficiency, and soil fertility. The effect of wheat residue incorporation with green manure (GM, Sesbania cannabina L.) on subsequent rice yields was also determined. Residue incorporation for 10 to 40 d had no effect on wheat yields. Rice yields increased (0.18–0.39 Mg ha−1) when wheat residue was incorporated with GM. Starter N applied at residue incorporation did not influence wheat yields but decreased N recovery efficiency. Physiological efficiency was higher when rice straw was incorporated in wheat and when wheat straw plus GM were incorporated in rice than when rice straw was incorporated for 10 d or when the straw was burned. The long‐term application of rice residue increased C accumulation in soil.

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