Impacts of rainfall-induced physical crust on near-surface soil pore structure after drying

Rainfall events in arid and semi-arid regions lead to the formation of a physical crust on the soil surface, and such crusts have significant implications for soil hydrological processes. However, previous research has primarily focused on the macroscopic effects of the physical crust, while the influence of soil moisture changes on the soil pore structure is poorly understood. In this study, we simulated two types of physical crusts (structural and depositional) under different rainfall durations using artificial rainfall simulations. We employed X-ray computed tomography (XCT) to analyze the geometric shapes and topological structures of the near-surface soil pores. The results revealed stratified characteristics of soil porosity caused by rainfall-induced physical crust. The porosity in the crustal layer was lower and exhibited a denser pore structure than that of the underlying soil. The thickness of the physical crust varied with the duration of rainfall, with depositional crusts thickening under longer rainfall durations, whereas the opposite was observed for structural crusts. Both types of physical crusts induced significant changes in the pore structure of the upper soil layer, including a decrease in average pore size and an increase in pore density. Analysis of pore connectivity indicated an increase in isolated pores within the physical crust, suggesting a reduction in soil permeability and airflow capacity. This study contributes insights for agricultural soil management in arid and semi-arid regions by revealing the nuanced effects of rainfallinduced physical crusts on near-surface soil pore characteristics.