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.