Seasonal variations in the influence of vegetation cover on soil water on the loess hillslope

Soil water is the key factor that restricts the restoration of the local ecological systems in the Loess Plateau of China. Studying the effects of vegetation types on soil water and its seasonal variation helps to understand hydrological characteristics and provides insights into the sustainable restoration of vegetation. Therefore, the Caijiachuan watershed was chosen as the research object to investigate the water status of a 0–10 m soil layer under different vegetation types including Pinus tabulaeformis, Robinia pseudoacacia, Platycladus orientalis , apple orchard, natural forestland, farmland and grassland. By comparing the difference between soil water of different land use types and that of grassland during the same period, the seasonal changes of soil water status of different types were judged. The results show that (1) in the 0–10 m soil layer, the largest value of soil water content was in the 0.3–0.4 m layer, and the lowest was in the 5.6–5.8 m layer. The depths at which the vegetation cover influenced the soil water were up to 10 m; (2) among summer, fall and spring, the soil water storage was the highest in the fall. In addition, the lowest value of relative accumulation was in the fall, which was the period in which the soil water recovered; (3) the soil water in the 0–10 m layer was in a relatively deficient state in the artificial forestlands, apple orchards and native forestlands, while the relative accumulation was in the farmland. In addition, the relative deep soil layers (8–10 m) had more serious deficits in the areas in which P. tabulaeformis, R. pseudoacacia and the apple orchard grew; (4) during the study period, the farmland in the summer had the largest relative accumulation (182.71 mm), and the land under R. pseudoacacia in the fall had the lowest relative deficit (512.20 mm). In the Loess Plateau, vegetation cover will affect the change of deep soil moisture and artificial forest will cause soil water loss in different degrees.