Long-term effects of different land use and soil management on various organic carbon fractions in an Inceptisol of subtropical India

Land use changes, especially the conversion of native forest vegetation to cropland and plantations in tropical regions, can potentially alter soil C dynamics. A study was conducted to assess the effects of various land uses and soil managements (agro-forestry plantation, vegetable field, tube-well irrigated rice-wheat, sewage-irrigated rice-wheat, and uncultivated soils) on soil pH, bulk density, soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), C mineralisation (Cmin), microbial quotient, and microbial metabolic quotient (q CO2 ) in 0-0.05, 0.05-0.10, and 0.10-0.20 m soil depths. At 0-0.05 m, the bulk density was lowest (1.29 Mg/m 3 ) in agro-forestry soil, whereas the uncultivated soil (jointly with vegetable field soil) showed highest bulk density (1.48 Mg/m 3 ). Sewage-irrigated rice-wheat soil showed lowest pH particularly in the 0-0.05 and 0.10-0.20 m soil layer. Irrespective of soil depths, agro-forestry plantation showed greater SOC followed by sewage-irrigated rice-wheat soil. Nevertheless, agro-forestry soil also showed highest stock of SOC (33.7 Mg/ha), POC (3.58 Mg/ha), and MBC (0.81 Mg/ha) in the 0-0.20 m soil layer. Sewage-irrigated rice-wheat jointly with agro-forestry soil showed greatest Cmin in the 0-0.20 m soil layer, although the former supported lower SOC stock. The decrease in SOC (SOC0-0.05 m/SOC0.10-0.20 m) and Cmin (Cmin 0-0.05 m/Cmin 0.10-0.20 m) along soil depth was significantly higher in the agro-forestry system than in most of the other land use and soil management systems. Microbial quotient was highest in sewage-irrigated rice-wheat soil, particularly in the 0-0.05 m soil depth, whereas q CO2 was greater in uncultivated soil. In general, microbial quotients decreased, whereas q CO2 increased down the soil profile.