Long-term effect of nutrient management on soil fertility and soil organic carbon pools under a 6-year-old pearl millet–wheat cropping system in an Inceptisol of subtropical India

We studied the long-term effect of nutrient management on soil fertility and soil organic carbon (SOC) pools under a 6-year-old pearl millet–wheat cropping system in an Inceptisol of subtropical India. Significant build-up in soil fertility in terms of alkaline KMnO4-N, Olsen-P, NH4OAc-K and CaCl2-S as well as SOC pools namely, total organic carbon (TOC), Walkley and Black organic carbon (WBC), labile organic carbon (LBC) and microbial biomass carbon (MBC) were maintained under FYM and integrated nutrient management involving FYM and NPK than unfertilized control plot in 0–15 and 15–30 cm soil depths. The highest values of TOC (11.48 g kg−1) and WBC (7.86 g kg−1) were maintained in FYM treated plot, while the highest values of LBC (1.36 g kg−1) and MBC (273 mg kg−1) were found in FYM + NPK. The magnitude of change in pools of SOC in sub-surface (15–30 cm) soil was low as compared to the surface soil (0–15 cm). Significant increase in all the pools of SOC in FYM treated plots indicates the importance of application of organic manure like FYM in maintaining organic carbon in soil. Highly strong relationships were exhibited between LBC and MBC with yield, indicating that these pools are more important for nutrient turn-over and their availability to plants than total SOC. Carbon management index revealed that integrated nutrient management could be followed for enhancing crop productivity, nutrient availability and soil carbon pools for long-term. These results conclude that for sustainable crop production and maintaining soil quality, input of organic manure like FYM is of major importance and should be advocated in the nutrient management of intensive cropping system for improving soil fertility and biological properties of soils.

► Soil fertility and SOC pools increased significantly in FYM and FYM + NPK treated plots.
► FYM treated plot increased TOC and WBC, while FYM + NPK increased LBC and MBC in soil.
► Strong relationships were exhibited between LBC and MBC with yield than total SOC.
► Integrated nutrient management improved C management index for sustainable crop production.
► FYM should be advocated for maintaining soil fertility and SOC pools for long-term.