Biochar with wheat straw and farmyard manure modulate microbial activity by inducing qualitative and quantitative changes in soil organic carbon in saline, sodic and saline-sodic soils

Soil salinity is a global soil degradation issue and poses significant threats to soil quality and food security. Saline soils are inherently poor in soil organic matter, microbial activity and plant available nutrients. We investigated the effects of biochar (BC), wheat straw (WS) and farmyard manure (FYM) on microbial activity, qualitative and quantitative soil organic carbon (SOC) dynamics, activities of extracellular enzymes and nutrient availability in saline, sodic and saline-sodic soils. The incubation study followed completely randomized experimental design consisting of six treatments: (1) unamended control; (2) BC, derived from corncob biowaste (2%, w/w basis); (3) WS(2% w/w); (4) FYM (2%, w/w); (5) BC+WS (each 1%, w/w); and, (6) BC+FYM (each 1%, w/w). Biochar significantly reduced decomposition of WS and FYM in saline soils. Biochar with and without WS and FYM significantly reduced soil pH and electrical conductivity (EC) in all saline soils. Biochar promoted microbial activity by significantly increasing microbial biomass carbon (C), nitrogen (N) and phosphorus (P) and nutrient pools in all saline soils but much higher in sodic soil. Soil microbial biomass and mineral nutrients corresponded positively to soil dehydrogenase, β-glucosidase, urease and alkaline phosphomonesterase enzymatic activities. Biochar also significantly enhanced extractable (cold- and hot-water) WEOC and total SOC contents when applied with WS and FYM. Biochar with WS and FYM significantly reduced dissolved organic C (DOC) contents suggesting higher C retention resulted from changes in SOC quality as indicated from the specific ultraviolet absorbance (SUVA) and E2/E3 ratio. Biochar reduced C mineralization of fresh organic matter (WS and FYM), retained more C, improved soil biochemical functions and altered SOC quality. We conclude that BC along with other fresh organic matter inputs can improve soil organic matter cycling and biochemical functions to restore soil quality and health in saline soils.