Seasonal and Long-Term Variability in Soil Structure and Erodibility under Different Land-Use Patterns in the Mollisols Region of Northeast China

Soil structure and its change are good indicators for soil quality and environmental stability, and land-use change is known to be an important factor that affects soil structure. We investigated the seasonal and temporal variability in the soil structure and evaluated soil erodibility under different land-use and land-management practices in the Mollisols region of Northeast China. We considered five land-use and land-management modes in the sloping land (5 degrees), i.e., bare land (BL), natural vegetation restoration (NVR), artificial forest (AF), no-tillage (NT), and conventional tillage (CT). The bulk density (BD), aggregate size distribution, and aggregate stability (AS) were determined for each mode. Meanwhile, we estimated the runoff depth (RD) and sediment yield (SY) to assess the soil erodibility. The lowest BD in CT occurred in May, but no seasonal change in BD was observed in other treatments. After 15 years, the NVR and CT had increased BD values, while the BD of NT declined significantly over time. The >2 mm size fractions and the AS of NVR, NT, and CT were the largest in August, while those of BL decreased during the growing season. Furthermore, the >2 mm size fractions and the AS of BL, NT, and CT decreased over the long-term study period, but NVR and AF exhibited no significant inter-annual changes in the AS. The BD and AS in NVR and AF were greater than those in BL. After 15 years, the BD of NT and CT were not significantly different, but NT had a greater AS. The AS was greater in the subsurface soil than in the topsoil of NT and CT. Moreover, the NVR and NT had significantly reduced RD and SY compared with BL and CT. These results provide a scientific basis for choosing sustainable agriculture and land development modes to control soil erosion in Northeast China.