Managing crop residue with green manure, urea, and tillage in a rice-wheat rotation

Most double-crop grain farmers in South Asia remove or burn crop residue to facilitate seedbed preparation and to avoid possible yield reductions. This results in loss of soil organic matter (SOM) and nutrients, In this study, we determined whether incorporating wheat (Triticum aestivum L.) residue, rice (Oryza sativa L.) residue, and sesbania (Sesbania aculeta L,) green manure with urea fertilizer N in a rite-wheat cropping system can improve grain yields, N use efficiency, and SOM, We incorporated wheat residue (6 Mg ha(-1), C/N = 94), rice residue (6 Mg ha(-1), C/N = 63), or both, with and without green manure (20 or 40 Mg fresh ha(-1), C/N = 19), in a field experiment with irrigated rice and wheat grown each year in rotation on a Tolewal sandy loam (Typic Ustochrept) in the Punjab of India. Rice and wheat residue did not affect grain yields of wheat and rice, but residue incorporation did result in reduced recovery efficiency of urea N and green manure N, Rice production was greater with wheat residue incorporation when an average of 86 kg N ha(-1) of a prescribed 120 kg N ha(-1) dose was applied as green manure N and the balance as urea N vs. 120 kg urea N ha(-1) alone. Despite wider C/N than rice residue, wheat residue additions to flooded rice resulted in greater C sequestration in soil than with rice residue or 40 Mg green manure ha(-1), These results demonstrate that a green manure crop and/or incorporating crop residue in a rice-wheat system has potential to increase SOM while maintaining high grain yields.