Rice-wheat cropping system: assessment of sustainability under green manuring and chemical fertilizer inputs

Rice-wheat rotations are the most important cropping system of the Indo-Gangetic plains. We measured the long-term sustainability of the system for green manuring and chemical fertilizer input practices utilising the trends in grain yield, partial factor productivity (PFP), agronomic efficiency, benefit:cost ratio, soil organic carbon content (OC) and sustainable yield index (SM). The data of a long-term experiment conducted at six locations in the Indo-Gangetic plain region of India revealed that grain yield and PFP of both rice and wheat declined under control (no fertilizer, no green manure) and sub-optimal fertilizer inputs (50 or 75% recommended fertilizer NPK) at all locations. Complete dose of fertilizer NPK (100% recommended) increased grain yields as well as PFP in rice but did not prevent decline in these parameters in wheat. Partial substitution of chemical fertilizer with Sesbania green manure, however, brought further improvement in yield and PFP in rice and the residual effect of green manure reversed the declining trend in wheat. The SYI and agronomic efficiency of fertilizers were also greater in plots receiving 100% fertilizer NPK or green manuring along with 50 or 75% recommended NPK. Benefit : cost ratio of fertilizer inputs and green manuring practices increased in both crops and for all treatments, indicating that the benefit accruing from fertilizer improved with time. At locations with high initial OC, a depletion of OC was noticed whereas OC increased at locations with low initial OC, with OC stabilizing between 0.60 and 0.65%. Trends in grain yield, PFP and agronomic efficiency of fertilizer appear promising tools to measure sustainability of fertilizer management practices. (C) 2000 Elsevier Science B.V. All rights reserved.