Effects of straw returning methods on seasonal variation in soil moisture and water storage in Mollisols with different degradation degrees

Straw return has been widely implemented to mitigate soil erosion in agricultural land. However, the influences of straw returning method on soil moisture dynamics and water storage capacity in croplands with varying degradation degrees remain unclear. To address these knowledge gaps, seasonal variations in soil moisture and water storage in 0–100 cm soil layer were monitored throughout the soybean growing season (2023) in the black soil region of northeastern China. Four straw returning methods, namely rotary tillage (SR), deep plowing (SP), strip mulching (SM) and straw removal (CK), were evaluated across croplands with four degradation degrees: non-degradation (ND), light (LD), moderate (MD) and severe degradation (SD). The findings demonstrated that soil moisture changed greatly with soybean growth stages, especially for SP and CK treatments, with coefficients of variation ranged from 1.3 % to 18.8 % and from 0.7 % to 15.8 %. With land degradation degree intensifying, 0–60 cm soil water storage decreased from 220.2 mm to 152.4 mm. Compared to CK, soil water storage (0–60 cm) increased by 2.8–10.6 %, −5.0–3.8 %, and 15.0–19.3 % for SR, SP and SM treatments, respectively. SR method was recommended for non-degraded cropland, whereas SM method should be applied for degraded croplands. The mechanisms of straw returning method regulating soil water storage were primarily related to the resultant changes in soil porosity, temperature, and the capacity to capture rainfall. This study provides valuable insights for choosing the appropriate straw management practice to promote rainfall use efficiency in sloping farmlands, particularly in semi-humid regions.