Carbon dynamics, potential and cost of carbon sequestration in double rice cropping system in semi arid southern India

Studying the dynamics of soil organic carbon (SOC) is important for understanding the mechanistic pathways of C stabilization into different SOC pools.An attempt was, therefore, made to assess the impact of double rice cropping system with different levels of fertilizers and in combination with organics on C sequestration and its stabilization in an Inceptisol using a 14-year old experiment at Jagtial under semi-arid climate in India.Total organic carbon (TOC) allocated into different pools in order of very labile > less labile > non labile > labile, constituting about 41.4, 20.6, 19.3 and 18.7%, respectively.In comparison with control, system receiving farmyard manure (FYM-10 Mg ha -1 season -1 ) alone showed greater C build up (40.5%) followed by 100% NPK+FYM (120:60:40 kg N,P,K ha -1 +5 Mg FYM ha -1 season -1 )(16.2%).In fact, a net depletion of carbon stock was observed with 50% NPK (-1.2 Mg ha -1 ) and control (-1.8 Mg ha -1 ) treatments.Only 28.9% of C applied through FYM was stabilized as SOC.A minimal input of 2.34 Mg C ha -1 y -1 is needed to maintain SOC level.Treatments with organics showed a higher carbon management index, and microbial biomass and other labile pools of SOC.Results also indicated that100% NPK+FYM could maintain yield sustainability with a lower cost of carbon sequestration.