Long-term effect of different integrated nutrient management on soil organic carbon and its fractions and sustainability of rice-wheat system in Indo Gangetic Plains of India

Rice-wheat rotation is the most important cropping system of the Indo-Gangetic Plains (IGP) and is responsible for the food security of the region. The effect of different integrated nutrient management practices on soil organic carbon (SOC) stocks and its fractions, SOC sequestration potential as well as the sustainability of the rice-wheat system were evaluated in long term experiments at different agro-climatic zones of IGP. Application of NPK either through inorganic fertilizers or through combination of inorganic fertilizer and organics such as farm yard manure (FYM) or crop residue or green manure improved the SOC, particulate organic carbon (POC), microbial biomass carbon (MBC) concentration and their sequestration rate. Application of 50% NPK + 50% N through FYM in rice and 100% NPK in wheat, sequestered 0.39, 0.50, 0.51 and 0.62 Mg C ha(-1) yr(-1) over control (no N-P-K fertilizers or organics), respectively at Ludhiana, Kanpur, Sabour and Kalyani using the mass of SOC in the control treatment as reference point. Soil carbon sequestration with response to application of fertilizer partially substituted (50% on N basis) with organics were higher in Kalyani and Sabour lying in humid climate than Ludhiana and Kanpur lying in semiarid climate. The rice yield recorded a significant declining trend in Ludhiana and Kanpur where as the yield trend was stable at Sabour and Kalyani under unfertilized control. The system productivity in N-P-K fertilized plots and NPK along with organics showed either an increasing trend or remained stable at all locations during last two and half decades of the experiment. (C) 2011 Elsevier B.V. All rights reserved,