Regulatory mechanisms of soil water spatiotemporal dynamics driven by land use in a terraced watershed on the Loess Plateau.

Over the past three decades, large-scale terrace construction, vegetation restoration, and economic forest expansion have profoundly reshaped watershed geomorphology and vegetation patterns across the Loess Plateau, while altering soil water regimes. Terrace security and vegetation sustainability caused by soil water changes have become key issues. In this study, we propose a novel multi-paired sampling method to eliminate the interference of site conditions, and enable accurate quantification of the effects of terraced land use types on soil water. A total of 32 paired sampling groups (107 plots) were selected, including cropland, abandoned land, orchard, and forest land. Soil water content was measured eight times from 2023 to 2025 at 20 cm intervals within the 1 m soil profile. The results showed that compared with cropland, the soil water storage of forest land, orchard, and abandoned land decreased by 86.74 ± 19.54 mm, 31.58 ± 19.47 mm, and 33.24 ± 21.00 mm, respectively. The contribution of soil water variance components exhibited clear seasonality, which was highly dependent on soil depth and land use type. The contribution of the temporal anomaly component in total variance decreased with soil depth. Forest land exhibited the highest contribution of temporal anomalies to spatial variance, followed by cropland and orchard, while abandoned land exhibited the lowest contribution. Empirical orthogonal function and PLS-SEM analysis revealed that land use was the dominant factor affecting soil water storage capacity. Vegetation canopies regulate rainfall interception and water flux, alter soil hydrological properties, and collectively control soil water dynamics. Additionally, topographic effects on soil water storage and dynamics are almost negligible in the watershed due to terrace engineering and land use patterns. This study clarifies the mechanism of soil water response to terrace land use conversion, and provides scientific basis for terrace management and vegetation configuration in semi-arid areas.