Soil organic carbon fractions and management index after 20 yr of manure and fertilizer application for greenhouse vegetables

Impacts of organic manure and inorganic fertilizer on total organic carbon (C T ), water‐soluble organic C (C WS ), microbial biomass C (C MB ), particulate organic C (C P ), labile organic C (C L ), C storage and sequestration, and C management index (CMI) in surface soil (0–20 cm) were investigated in a 20‐yr field experiment under a greenhouse vegetable system in northeast China. The treatments included unfertilized control (CK), N fertilizer (N), balanced NPK fertilizer (NPK), organic manure alone (M) and the NPK fertilizer combined with the manure (MNPK). Under the treatments of N and NPK, C T content and C storage were not significantly changed over the experimental period, while C WS , C MB , C P , C L concentrations and CMI were significantly increased compared with the unfertilized control. In comparison with the control, the manure treatments, M and MNPK, significantly increased C T content and C storage, sequestrating organic C of 8.9 and 9.2 Mg/ha, respectively. The M and MNPK treatments showed higher C WS , C MB , C P and C L concentrations and CMI than the other three treatments. Pearson’s correlation coefficients were used to show that C WS , C MB , C P , C L and CMI could be useful indicators for assessing soil quality and total C changes. The M treatment is effective in sequestrating soil C, but resulted in lower crop yield compared with the NPK treatment. The MNPK treatment showed the greatest increases in crop yield and C sequestration in the greenhouse vegetable system.