Spatio-temporal variability and temporal stability of water contents distributed within soil profiles at a hillslope scale

Abstract

Information about soil water content (SWC) within soil profiles in terms of its spatio-temporal variability and temporal stability is crucial when selecting appropriate soil water management practices. However, detailed profile distribution features for related indices are not clear on the Chinese Loess Plateau. This study aimed to investigate the depth dependency of spatio-temporal variability and temporal stability of SWC at the hillslope scale using an intensive sampling strategy for both horizontal and vertical directions as well as over time. The SWCs at 20 depths within 0–300cm soil profiles were measured on 20 occasions between July 2008 and October 2010 at 91 locations on a hillslope on the Loess Plateau, China. Results showed that although the profile distributions of investigated statistical parameters differed greatly, they were all depth dependent. Based on both the spatio-temporal variability and the temporal stability characteristics using eight indices, the studied soil profile (0–300cm) could be divided into three soil layers, i.e., 0–60, 60–160 and 160–300cm, with a characteristic feature of “irregularly changing”, “regularly changing”, and “relatively constant”, respectively. The deepest rainwater replenishment depth was approximately 160cm. Therefore, choosing 200cm as the sampling depth would be sufficient in similar areas. Such findings are useful for designing an optimal strategy for sampling and management of profile soil moisture.