Profile distribution of soil moisture in the gully on the northern Loess Plateau, China

Gully is a typical geographical unit and a key component of the slope-gully system on the northern Loess Plateau. Understanding the distribution of soil moisture in gullies aids water resource regulation and ecological restoration. To investigate temporal-spatial variability of soil moisture, we measured values of soil water content (SWC) within 0-500 cm by using a neutron probe on 19 occasions from October 2014 to July 2017 in the gully and bank of a developed gully in Liudaogou catchment of Shenmu County. Results showed that the values of space-averaged soil water storage (SWS) in the gully were significantly (P < 0.01) higher than those in the bank. Soil clay content (SCC) and topography (including site elevation and distance from the gully head) were the most important factors affecting SWS of 0-500 cm in the gully. Topography can indirectly control SWS by redistribution of rainfall and soil properties. SWS and SCC rose with increasing distance from the gully head to the outlet. SWS in the gully exhibited strong temporal stability, and two time-stable sites around the middle section can be used to represent mean SWS within 500 cm depth in the gully. The gully sidewall significantly (P < 0.05) aggravated drought of soils in the bank between 150 and 250 cm from the gully edge. Gullies make the temporal-spatial patterns of soil moisture complex in slope-gully system. These results were expected to improve understanding of soil moisture distribution in the gully region and aid vegetative restoration of the northern Loess Plateau.