Abstract: Based on a 21-year long-term no-tillage and straw-returning test, aimed to analyze the effects of long-term no-tillage and straw-returning on soil SOC(Soil organic carbon) and its components in the surface and subsoil(0−60cm) in the winter wheat growing period. This long-term fixed experiment started in 1992，included straw-returning under no-tillage(NT) and conventional tillage(CT), two field management methods. The chemical fertilizer was applied to the two treatment are same. After 20-year later, soil samples in different layers and wheat growth period were collected. Soil organic carbon(SOC), soil microbial biomass carbon(MBC), and soil particulate organic carbon(POC) were measured, soil soluble carbon(DOC) content in different soil layers and growth period. Compared with CT, NT significantly changed the distribution of MBC, POC, and DOC of 0−30cm soil layer in the five growth stages before sowing, before winter, jointing, anthesis, and maturity. Furthermore, NT significantly improved their soil contents in the five stages(P<0.05), specifically, in comparison, MBC, POC, and DOC in the five growth stages increased averagely by 60.8%−161.4%, 71.8%−141.1%, and 21.9%−104.4%, respectively. Besides, there is a great influence on SOC content in the 0−20cm soil layer by applying no-tillage and straw-returning; the average SOC content of 0−5cm and 5−10cm soil increased 81.2% and 52.9%, respectively. However, this similar influence did not appear in the 5-growth period. In the layer of 0−60cm, the contents of SOC, MBC, POC, and DOC under two tillage methods all showed a downward trend with soil depth growth. The organic carbon content of surface soil(0−20cm) and the level of active organic carbon(MBC, POC, DOC) in the wheat-growing time were significantly improved after applying no-tillage and straw-returning. This study showed that long-term no-tillage could raise the soil organic carbon content and active organic carbon level during the wheat growing season, which provides a theoretical basis for the efficient storage of organic carbon in dryland soil.

Key words: Soil organic carbon, Soil labile organic carbon, No-tillage straw returning, Winter wheat, Dryland in the North