Effects of carbon input on soil carbon stability and nitrogen dynamics

Improved understanding of the process of carbon (C) stabilization is critical to managing emissions from agricultural soils and optimizing crop yield. We assessed soil organic C (SOC) stability and nitrogen (N) dynamics in a long-term fertilization experiment (started in 1972) conducted at three different locations in India (Jabalpur-Vertisol, Palampur-Alfisol and Ranchi-Alfisol). We measured soil organic C (SOC), C pools and stocks in the treatments of no fertilization as control, inorganic fertilization as NPK and integrated fertilization as NPK + farm yard manure (FYM). Quantification of different SOC pools was done by a procedure of acid hydrolysis followed by a long-term (247 days) incubation study. Based on crop yield and C storage, NPK + FYM was the best treatment for improving crop productivity and SOC sequestration. Integrated fertilization for 38 years increased SOC across sites. In the NPK treatment, additional C input (3–9 times higher) in the form of root biomass did not significantly change C pools. Application of FYM in addition to NPK enhanced the acid non-hydrolysable fraction of SOC across sites. Stability of SOC significantly influenced N dynamics in soil and the availability of N in soil is correlated with the amount of C in the acid-hydrolysable pool (R2 = 0.64, p = 0.01) but not with SOC (R2 = 0.12, p = 0.01). Long-term use of chemical fertilizers did not significantly affect soil total N content.