The Effect of Simulated Precipitation Changes on the Recovery of Soil Water Infiltration Characteristics in Grasslands in the Loess Hilly Region

Current climate change has led to significant changes in precipitation patterns in the Loess Hilly Region, resulting in frequent extreme rainfall events, which have a significant impact on restoring the soil hydrological function of grasslands in this area. This study focuses on the restoration of grasslands through the conversion of farmland in the Loess Hilly Region. Using natural rainfall as the control, seven precipitation gradient treatments were established with rainout shelters: +20%, +40%, and +60% rainfall increases, and −20%, −40%, and −60% rainfall decreases. The changes in infiltration characteristics were then analyzed. Long-term increased rainfall promoted vegetation restoration and improved soil physicochemical properties. Compared with the natural rainfall control, the +20%, +40%, and +60% rainfall increase treatments enhanced the total porosity of the 0–5 cm soil layer by 0.29%, 4.64%, and 3.18%, respectively, and increased the soil organic carbon content by 28.42%, 62.46%, and 63.16%, respectively. Soil infiltration rate was also enhanced accordingly. Relative to the steady-state infiltration rate of the control (4.76 mm/min), the +20%, +40%, and +60% treatments increased the rate by 1.13%, 16.67%, and 22.54%, respectively, with the +60% treatment achieving the highest steady-state infiltration rate of 5.83 mm/min. The macroaggregate content in the +40% treatment was 47.70%, which was significantly higher than that in the other treatments. The increase in infiltration was related to the increase in total porosity, organic carbon, and the content and stability of large aggregates. Moderate rainfall increases can promote organic carbon accumulation and the formation of large aggregates, enhancing soil infiltration capacity; however, rainfall intensities exceeding 60% can damage the soil structure, and infiltration no longer significantly increases.