Organic Amendments Influence Soil Organic Carbon Pools and Rice–Wheat Productivity

Soil organic C (SOC) pools under long‐term management practices provide information on C sequestration pathways, soil quality maintenance, and crop productivity. Farmyard manure (FYM), paddy straw (PS), and green manure (GM) along with inorganic fertilizers were used in a 19‐yr‐old rice ( Oryza sativa L.)–wheat ( Triticum aestivum L.) cropping system in subtropical India to evaluate their impact on SOC stock, its different pools—total organic C (C tot ); oxidizable organic C (C oc ) and its four fractions of very labile (C frac1 ), labile (C frac2 ), less labile (C frac3 ), and nonlabile C (C frac4 ); microbial biomass C (C mic ); and mineralizable C (C min ). Cropping with only N–P–K fertilization just maintained SOC content, while N–P–K plus organics increased SOC by 24.3% over the control, their relative efficacy being FYM > PS > GM. A minimum of 3.56 Mg C ha −1 yr −1 was required to be added as organic amendments to compensate for SOC loss from cropping. The passive (C frac3 + C frac4 ) pool and C min constituted about 39 and 11.5%, respectively, of C tot Organics contributed toward the passive pool in the order FYM > PS > GM. Most of the pools were significantly ( P = 0.005) correlated with each other. Yield and sustainable yield index were strongly related with C frac1 , C oc , C mic , and C min Results suggest C frac1 as a useful indicator for assessing soil health, and balanced fertilization with FYM as suitable management for sustaining crop productivity of the rice–wheat system.