Improving soil organic carbon and microbial functionality through different rice straw management approaches in rice–wheat cropping sequence

Rice straw (RS) produced enormously in India and around the globe demands viable solutions for management. Some practicable strategies could be the use of RS per se, preparation of biochar from rice straw (BC) and integrating application of BC with farmyard manure (FYMBC). To identify the most appropriate RS management practice, it is imperative to enumerate the effect of different amendments on soil organic carbon (SOC) pools and biological activity. The goal of this study was to explore the effect of different rates of RS, BC, and FYMBC on total organic C (TOC), water soluble (WSC), hot water soluble (HWSC), and microbial biomass (MBC) C and enzyme activities under a rice–wheat system. Application of RS and BC along with FYM (FYMBC) at both the rates (6 and 12 t ha−1) and BC alone at 12 t ha−1 significantly (p < 0.05) improved total and labile SOC pools. The enrichment of SOC pools differed with the composition of the organic amendment; RS enriched WSC pool to a greater extent whereas BC and FYMBC enriched HWSC pool more. The RS-amended soils evinced significantly higher C-cycle enzymes and phosphatase activities than BC and FYMBC soils. Dehydrogenase, xylanase, and cellulase together with labile C pools could predict the response of TOC to management, stipulating that characterizing the effect of various amendments requires a composite of parameters. The results suggested that the addition of BC either alone or along with FYM may be preferred as it leads to greater soil C storage and thus provides viable residue management and climate change mitigation strategy.