Temporal persistence and stability of soil water storage after rainfall on terrace land

The “Grain for Green” Project on the Loess Plateau of China has converted a large area of cultivated slope farmland to terraces to reduce soil erosion and improve the ecological environment. The area of terraced land on the Loess Plateau was 32,600 km² in 2010. Knowledge of the behavior of soil water storage (SWS) and its spatiotemporal distribution provides essential information concerning hydrological and ecological processes. This study aimed to analyze the temporal stability of SWS after rainfall for different time periods on terraces planted with jujube trees (Ziziphus jujuba Mill.). The SWS of 21 locations was obtained from July 19 to September 3 in 2014 and from August 01 to August 31 in 2015. Relative difference analysis and the nonparametric Spearman rank correlation test were used to check the temporal stability of SWS. The SWS on terraces was normally distributed and demonstrated moderate spatial variability. The SWS at three soil depths all showed strong temporal stability with stability in the order of 0–0.6 < 0–1.0 < 0–1.6 m. Rainfall significantly affected the temporal stability of SWS in the depth of 0–0.6 m. The number of representative locations of SWS was not constant. The best representative locations were not identical for different soil depths; however, a common representative location did exist for the different depths and periods. Moreover, the mean SWS generally increased from the upper to lower slope. The temporal stability of SWS was not significantly affected by rainfall but was significantly negatively correlated with sand content. The total root length and soil organic carbon content did not show any obvious correlations with mean SWS. It was feasible to use the representative locations of SWS to represent the mean SWS over a period of time. However, the cumulative absolute error increased with cumulative days. In conclusion, SWS in the deeper soil depths indicated greater temporal stability than that in shallow soil depth during wet period. The best representative locations for SWS were depth and time dependent.