Effects of carbon input on soil carbon stability and nitrogen dynamics

• Soil carbon stability and nitrogen dynamics in long-term experiment was analyzed.
• Application of FYM in addition to NPK produced greater size of resistant C pool.
• Additional carbon input in NPK plot had no effect on resistant carbon pool.
• Carbon stability significantly affected the N dynamics in soil.
• N availability in soil is linearly related with acid-hydrolyzable C pool.

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.