This study aims to determine the effect of straw return depth on soil physicochemical properties and enzymes activity, as well as the relationship between them under different straw return depth. In an in-situ field experiment with micro-plots conducted for 3 years (2016—2018), totally six treatments were set as straw (S1, straw incorporation; S2, straw removal) and rotary tillage depth factors (D1, 10 cm; D2, 20 cm; D3, 30 cm). And the individual and interactional effects on soil physical and chemical properties and enzymes activity of spring maize filed were determined in northeast China. Results indicated that: (1) soil organic carbon (SOC) was significantly affected by rotary tillage depth (D) and its interaction with straw (S) treatment (P<0.05), SOC contents under S1D1 and S1D2 were respectively 16.9% and 14.6% higher than S1D3 treatment at 0~20 cm soil layer, while the highest SOC content at 20~40 cm soil layer was observed from S2D3 treatment. (2) Soil nitrate (NO3--N) and ammonium (NH4+-N) contents, invertase and catalase activities were significantly influenced by straw and rotary-till depth treatments as well as their interaction (P<0.05). Across 0~40 cm soil layer, S1 treatment increased average 46.9% and 34.9% soil NO3--N contents under D1 and D2 conditions, but lowered average 31.6% and 4.4% soil NH4+-N contents, compared with S2 treatment. Among treatments of rotary-till depth, S1 treatment enhanced the soil invertase and urease activities at 0~20 cm layer and decreased catalase activity at 20~30 cm layer, compared to S2 treatment. (3) Correlation analysis presented that a significantly positive correlation existed between SOC, TN and soil NO3--N, NH4+-N content, as well as invertase. Both SOC and TN were highly negatively correlated with soil pH and SWC. The principal component analysis (PCA) suggested that SOC, soil TN, NO3--N content and enzymes activity were improved by S1D2 treatments in 0~40 cm soil layer, and by S1D1 and S1D3 treatments in 0~20 cm and 20~40 cm soil layer, respectively. Overall, soil nutrients level and enzymes activity in 0~40 cm layer were improved by S1D2 treatment, it might be considered as a suitable straw incorporation method for improving soil fertility in the maize field within study area. |