| Water resources are in extreme shortage on the Loess Plateau, where serious soil erosion and drought often take place, so how to use soil water resources reasonably and effectively is of great importance to meet physiological water requirements of vegetation and improve eco-environment. According to the current problems occurring during the process of vegetation rehabilitation on the Plateau, soil water that restricts vegetation construction primarily is focused on. In this dissertation, rainfall infiltration, runoff, and soil water redistribution on a hillslope were studied by simulated rainfall experiments, and soil water cycling was investigated by site observation and soil sampling methods. Moreover, the reasons for the desiccation of deep soil layer were analyzed, and its assessment indexes and standards were presented. The main results are as follows:(1) Rainfall infiltration into a planar hillslope with a homogeneous isotropic soil could be simply regarded as one-dimensional infiltration process, if soil erosion was prevented. The wetting front moved nearly parallel to the soil surface, and its length could be described by a power function of time, when the distribution of initial soil water was uniform. Infiltration mostly depended on matric potential gradient and the effect of upslope runoff could be omitted, when initial water content was very low.(2) Runoff-yielding time on grassland with a higher cover ratio primarily depended on initial water content, and their relationship might be described by a power function too. Surface crust could easily take place on bare land, so its runoff-yielding time primarily depended on rainfall intensity, and their relationship might be described by a linear function. In addition, bare land covered with weed would delay runoff-yielding time, increase infiltrated water, and make soil water move deeper.(3) When evaporation was stopped during the process of soil water redistribution, soil water would move downslope by gravity. When evaporation was in process, due to low initial water content, most infiltrated water from small intensity and amount of rainfall wouldbe consumed by intensive evapotranspiration during rainy season, and lateral downslope unsaturated flow seldom took place. However, soil water would move downslope by gravitational and matric potential gradients after continuous rainfall.(4) Wavy distribution of soil water along hillslope resulted from the fluctuation of runoff, upslope runoff infiltration, lateral downslope flow, and the difference of infiltration rate and evapotranspiration. The middle and lower parts of woodland and grassland had higher soil water contents during rainy season, which resulted from smaller evapotranspiration and more infiltrated water with a lower gradient. However, upslope runoff infiltration was another reason for hillslope with a lower cover ratio, such as bare land.(5) The vertical change of soil water in the profile was obviously different in layers. Based on the standard deviation and variation coefficient, soil water change in the profile could be divided into four layers by cluster analysis. Compared to bare land, soil water cycling on grassland with intensive transpiration was deeper in depth and greater in intensity.(6) The spatio-temporal change of soil water contents mostly depended on rainfall and evapotranspiration, and was seasonal. Based on rainfall and evaporation amount, the change of soil water could be divided into three main periods, such as decreasing of soil water storage in spring, alternatively decreasing and increasing in summer and autumn, and relatively stable in winter. Soil water storage decreased on the whole in summer and autumn during drought year, but increased during rainy year.(7) During the process of water consumption, soil water almost lost from the whole profile. The great depth that resulted from evapotranspiration formed soon, but not gradually. Infiltrated water was mostly consumed by evapotranspirat...
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