Objective Black soil, one of the most fertile soil types globally, is renowned for its deep humus layer and favorable structure, and serves as a crucial agricultural soil resource in China. However, in recent years, with the intensification of human activities, the black soil region has been confronted with severe challenges such as soil degradation and declining fertility. As a key manifestation of human activities, land use types profoundly affect the physical and chemical properties of soil, thereby influencing its ecological functions and production potential. Investigating the seasonal variations in soil physical properties under different land use types in black soil regions can provide a scientific basis for the protection and sustainable utilization of black soil.

Methods In this study, four typical land use types (bare land, cultivated land, grassland, and forestland) were selected. Soil samples from different soil layers were collected in April, June, August, and October, and physical indicators such as soil bulk density, soil mass water content, water-stable aggregate distribution, and aggregate stability (GMD and MWD) were determined.

Results 1) The soil bulk density in the 0−20 cm soil layer of bare land and cultivated land showed little seasonal variations. The soil bulk density of grassland in April was 7.4%−9.1% lower than in other periods, while that of forestland slightly increased in October. 2) The average soil mass water content in the 0−20 cm layer across all land use types reached its seasonal peak in August. Among them, the minimum soil water content of bare land occurred in April, while that of forestland, cultivated land, and grassland appeared in June. The seasonal differences in the coefficient of variation (CV) of water content were significant in bare land and cultivated land, whereas the CV values of forestland only varied within the range of 10.29%−11.63% across different seasons. 3) Water-stable aggregates > 0.25 mm were slightly affected by seasonal changes in forestland, followed by cultivated land and grassland and most affected in bare land. Soil aggregate stability indices showed the same trend.

Conclusions Soil bulk density fluctuations in cultivated land show strong correlations with the agricultural cycle, while those in forestland and grassland slightly increase in autumn. This differentiation supports soil quality regulation and field management. Forestland and grassland have the optimal soil water storage in summer, while cultivated land and bare land show poor water storage stability, suffering from water shortage in dry seasons, waterlogging in wet seasons, and low water use efficiency. Optimizing vegetation management in cultivated land can enhance soil water storage stability and alleviate seasonal water imbalance. The seasonal distribution of water-stable aggregates > 0.25 mm in forestland is minimally affected by seasonal variations, followed by that in cultivated land and grassland, while bare land is the most significantly affected by seasonal changes in this aspect. For the soil aggregate stability indices (GMD and MWD), the order is as follows: forestland > grassland > cultivated land > bare land. These findings demonstrate that vegetation coverage and land use types play a key regulatory role in soil structural stability, and maintaining or restoring vegetation coverage is an important measure to improve soil aggregate stability and mitigate soil degradation.