Spatiotemporal variations in deep soil moisture and its response to land-use shifts in the Wind–Water Erosion Crisscross Region in the Critical Zone of the Loess Plateau (2011–2015), China

Soil water content (SWC) with a deep profile is crucial to land use management, soil and water conservation, and ecological restoration worldwide, including the wind–water erosion crisscross region in the Critical Zone of the Chinese Loess Plateau. To ascertain the spatiotemporal variation of deep SWC and its response to land-use shifts in the region, the SWC was monitored at four representative land uses (farmland, shrubland, natural grassland, and planted grassland) to a depth of 21 m. Monitoring occurred between 2011 and 2015 in the Liudaogou watershed of the Chinese Loess Plateau. The Hydrus-1D model was then applied to simulate the SWC dynamics for the different land-use types and scenarios of land-use shifts. The SWC exhibited a high spatial variability in the vertical direction both within a given soil profile and among the different land uses. In the 0–2 m layer, the soil texture and root biomass controlled the spatial-temporal variability of the SWC. The temporal variability was also controlled by meteorological factors. In the 2–21 m layer, spatial variability was controlled by the soil texture, while soil texture and root biomass influenced the temporal variability of the SWC. The Hydrus-1D model accurately simulated spatiotemporal variations of SWC in the 0–21 m layer and was more effective on layers minimally influenced by weather. Land-use shifts from farmland with shallow-rooted plants to those with deep-rooted plants intensified soil water consumption in the 3.5–5 m layer. For best-management practices, appropriate plant species should be considered based on climatic conditions and SWC regimes. A better understanding of this information is useful for plant species selection, soil water resource utilization, and land use policymaking in the wind–water erosion crisscross region of the Critical Zone and other similar regions around the world.