Impacts of 22-year organic and inorganic N managements on soil organic C fractions in a maize field, northeast China

Impacts of 22-year organic and inorganic N managements on total organic carbon (TOC), water-soluble organic C (WSOC), microbial biomass C (MBC), particulate organic C (POC) and KMnO4 oxidized organic C (KMnO4-C) concentrations, C management index (CMI), and C storage in surface soil (0–20 cm) were investigated in a maize (Zea may L.) field experiment, Northeast China. The treatments included, CK: unfertilized control, M: organic manure (135 kg N ha− 1 year− 1), N: inorganic N fertilizer (135 kg N ha− 1 year− 1) and MN: combination of organic manure (67.5 kg N ha− 1 year− 1) and inorganic N fertilizer (67.5 kg N ha− 1 year− 1). TOC concentration and C storage were significantly increased under the M and MN treatments, but not under the inorganic N treatment. The organic treatments of M and MN were more effective in increasing WSOC, MBC, POC and KMnO4-C concentrations and CMI than the N treatment. The M treatment was most effective for sequestrating SOC (10.6 Mg ha− 1) and showed similar increase in degree of grain yield to the N and MN treatments, therefore it could be the best option for improving soil productivity and C storage in the maize cropping system.