Spatial variability of soil water for the entire profile in the critical zone of the Loess Plateau

Soil water is central to our understanding of water cycle, groundwater recharge and vegetation restoration in the critical zone of the Loess Plateau. To ascertain the spatial variability of soil water for the entire profile in the critical zone of the Loess Plateau, we obtained soil samples from the top of soil profile to bedrock in five typical sites (Yangling, Changwu, Fuxian, Ansai and Shenmu) based on soil core drilling and analyzed soil water vertical distribution, variation character and spatial structure in the entire soil profiles by classic statistics combining with geo-statistics. Results indicated that mean soil water content in the entire profile decreased at south-north direction in the critical zone of the Loess Plateau. Variabilities of soil water in the five sites all were moderate. Soil water variation in each site became weak gradually and difference in soil water content between the sites decreased as soil depth increased from 40 m to 200 m. Geo-statistics analysis demonstrated that semi-variogram of soil water content in the sites could be fitted well by theory model except Yangling site and exponential model could describe spatial variation structure in the most profiles. These results can benefit the understanding of soil water status and distribution regime in ultra-deep soil profile and are valuable for soil water resources estimation and vegetation restoration in the Loess Plateau.