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

Abstract

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 (Ctot); oxidizable organic C (Coc) and its four fractions of very labile (Cfrac1), labile (Cfrac2), less labile (Cfrac3), and nonlabile C (Cfrac4); microbial biomass C (Cmic); and mineralizable C (Cmin). 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 (Cfrac3 + Cfrac4) pool and Cmin constituted about 39 and 11.5%, respectively, of Ctot 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 Cfrac1, Coc, Cmic, and Cmin Results suggest Cfrac1 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.