Objective  The decline of soil organic carbon (TOC) is a key factor of black soil degradation. Investigating the effects of conservation tillage practices on SOC components is of great importance to stabilize black soil ecosystem, maintain fertility, and improve sustainable conservation tillage practices.

  Method  Maize and farmland black soil were taken as test crop and research objective, and conventional tillage (CT), conventional tillage + straw incorporation (CTSI), no-tillage (NT), no-tillage + straw incorporation (NTSI), subsoiling tillage (ST), and subsoiling tillage + straw incorporation (STSI) were established to investigate the quantity and structural characteristic of organic carbon (C) components in plough layer (0 - 20 cm) with density grouping method.

  Result  The results showed that the total SOC contents under conversation tillage treatments were all increased significantly compared with CT treatment. Light fraction organic C, coarse particulate organic C and fine particulate organic C contents in ST treatment were increased significantly (P < 0.05). Compared to straw removal, straw incorporation increased the organic C contents in each organic C component. Compared with NTSI treatment, the contents of light fraction organic C was increased significantly in CTSI treatment, while course particle organic C and fine particle organic C were both increased significantly in STSI treatment. Principal component analysis showed that the relative content of carbohydrate and polysaccharide functional groups in light faction organic C were all increased in NT, NTSI, ST and STSI treatments. Compared with CT, conservation tillage practices not only increased the relative content of active functional groups in the coarse-grained organic C and fine-grained organic C components, but also increased the relative content of stable functional groups, which was conducive to the formation of soil stability structure and promoted C sequestration. Tillage and straw incorporation significantly affected maize yield, ST was significantly higher than CT by 21.42% (P < 0.05). Straw incorporation increased maize yield with the highest yield in STSI treatment. Correlation analysis showed that fine particulate organic C could better indicate the change of organic C.

  Conclusion  It could be concluded that subsoiling tillage combined with straw incorporation is of great significance for stabilizing and increasing soil organic C content, maintaining SOC pool and enhancing maize yield.