Carbon and nitrogen mineralization kinetics in soil of rice–rice system under long term application of chemical fertilizers and farmyard manure

• Integrated application of NPK + FYM improved the mineralization potential of soil.
• Rates of mineralization of C and N were higher under aerobic condition.
• Microbial and mineralization quotients were also high under NPK + FYM and N + FYM.
• Amount of N mineralized is higher under aerobic and nutrient stress condition.

Quantitative information on carbon (C) and nitrogen (N) mineralization of soil under different long term nutrient management strategies is essential for better assessment of N availability and loss of C and N from soil. A laboratory incubation study was conducted with soils (0–15 cm and 15–30 cm depth), collected from 41 years of rice–rice system to evaluate the differences in C and N mineralization kinetics due to long term fertilization treatments-control (Non fertilized), N, NPK, FYM (Farmyard manure), N + FYM and NPK + FYM, and to assess the C and N mineralization rates in soil under different moisture regimes, i.e. aerobic and submergence. Both long term fertilization and moisture regime significantly affected C and N mineralization in soil. Long term integrated application of chemical fertilizer and organic manure (NPK + FYM, N + FYM) in soil resulted in higher potentially mineralizable C (C0), potentially mineralizable N (N0), rates of mineralization (dCmin/dt and dNmin/dt), microbial and mineralization quotients as compared to either of them applied alone (N, NPK, and FYM). Higher values of C0, N0, and rates of mineralization were recorded under aerobic condition than that under submergence. The amount of N released per unit C mineralization was higher in aerobic system that may result in greater loss of N from the system. A judicious N application strategy through integration of both organic and inorganic sources is essential for improving current N supplying capacity of soil and maintaining soil organic C pool in aerobic system.