Pools of organic carbon in soils under a long-term rice–rice system with different organic amendments in hot, sub-humid India

Study of soil organic carbon pools is helpful to understand the mechanism of carbon sequestration in soil. It was hypothesized that different management practices and sources of organics applied to soil will change the carbon allocation into various pools. The changes in total organic carbon (TOC) and its pools of different oxidizabilities (very labile, labile, less labile and non-labile pools) were investigated along with other fractions – microbial biomass carbon, particulate organic carbon, active carbon and oxidizable organic carbon – in soils under a 24-year-old double rice (Oryza sativa L.) cropping system with different management strategies in a hot, sub-humid region of India. Cultivation over the years caused a net buildup of TOC under different treatments. About 27.3, 48.2 and 54.1% of the C applied through green manure (GM), farmyard manure (FYM) and GM + FYM, respectively, was stabilized in the soils. Application of GM and FYM increased C in very labile and less labile pools, respectively. Of the analyzed pools, permanganate oxidizable and microbial biomass C were more sensitive to management practices and hence are considered important indicators of soil quality, and balanced fertilization with GM + FYM is considered suitable management for sustaining soil health under the double rice system.