Estimation and Restoration of Dried Soil Layers in a Slope-Gully Unit of the Chinese Loess Plateau

Dried soil layer (DSL) is a phenomenon of deep soil desiccation caused by soil water content (SWC) deficiency. Relevant studies in the fragmented terrain of Chinese Loess Plateau (CLP) remain limited. In a typical slope-gully unit near the Liudaogou catchment, SWC was measured using neutron probes on 19 occasions at 15 observational locations. In order to reveal the temporal stability and elimination degree of DSLs, available soil moisture (ASM) and DSL were estimated by representative sites which were determined through the temporal stability method, and the reliability of simulating mean condition of the study area via representative locations was assessed. Results show that: (1) the dynamics of DSL was characterised by complexity and diversity. The ASM within the DSL (DSL-ASM), ASM within the sandwiched DSL (SDSL-ASM) and quantitative index (QI) varied within the range of 2.75%–3.11%, 2.98%–4.22% and 0.254–0.356, respectively. (2) The possibility of development and recovery for DSL and SDSL in deep layers were less than that in shallow layers. The maximum depth of DSL (DSLMD) was significantly and negatively related to the standard deviation of relative difference (SDRD) of DSL-ASM, the maximum depth of SDSL (SDSLMD) was negatively related to the SDRD of SDSL-ASM. (3) The prediction results of ASM above 300 cm depth were more accurate than other layers (R² = 0.89). The DSL-ASM had more accurate ability of prediction than SDSL-ASM and QI. On the analysis of time stability characteristics of ASM and DSLs, the locations of A2 and C3 can better represent the mean conditions of ASM at three and four soil layers, respectively. C2, A1 and A1 can better represent the average levels of DSL-ASM, SDSL-ASM and QI, respectively (R² = 0.43, 0.14 and 0.18). (4) The restoration degrees of DSLs mainly showed no elimination and slight elimination, the DSLs cannot be completely eliminated within a short time. We proposed that scientific regulation of SWC can alleviate the formation and development of DSLs at a certain extent, and provide the possibility for DSLs nonoccurrence.