LAUSR

Abstract A 2-year field study was conducted with wheat (Triticum aestivum L.) - green gram (Vigna radiata L.) crop rotation in an inceptisol to compare the effect of vermicompost and biochar on soil organic carbon (SOC), its fractions and carbon mineralization when applied with inorganic fertilizers. Experimental treatments used were only inorganic nitrogen, phosphorus and potassium (NPK) at recommended dose as control, 50% N + PK, NPK + vermicompost (2.5 t ha−1), NPK + biochar (2.5 t ha−1), 50% N + PK + vermicompost (5 t ha−1) and 50% N + PK + biochar (5 t ha−1). Compared to lone application of inorganic fertilizers, application of organic amendments significantly increased the total organic carbon (4–10%), particulate organic carbon (POC) (5–21%), microbial biomass carbon (MBC) (40–55%), recalcitrant carbon (F4) (16–67%), humic acid carbon (HAC) (2–12%) and fulvic acid carbon (FAC) (8–37%). Higher concentration of labile carbon fractions (F1 and F2), POC and MBC were noted with vermicompost application while addition of biochar produced more stable carbon fractions (FAC, HAC and F4). Vermicompost application increased (5–15%) the C mineralization rate with higher (29–55%) soil respiration, and lower (35–58%) C half-life compared to biochar. Principal component analysis confirmed a close association among the stable C fractions (FAC, HAC and F4) and degree of humification. Labile carbon fractions (F1, F2 and MBC) indicated higher sensitivity to the applied fertilizers. Biochar application promoted higher leaf and root biomass in the tested crops whereas the grain yields were not significantly (P ≤ 0.038) different suggesting equal potentiality of both the amendments towards productivity. The benefit cost ratio was higher (1.89 and 2.89) for application of vermicompost but greater agronomic efficiency (0.10 and 0.12 kg kg−1) and lower (10–22%) soil available nitrogen content were noted with biochar application, which indicates environmental sustainability. Thus, biochar introduction into the fertility program of wheat-green gram crop rotation along with inorganic fertilizers would be a better option which not only uphold crop productivity but also sequester higher SOC compared to vermicompost.