[Water cycling characteristics of grassland and bare land soils on Loess Plateau]

The study under natural and simulated rainfall conditions showed that the variance coefficient of soil water in the grassland and bare land on Loess Plateau decreased with increasing soil depth, and the vertical change of soil water in drought year in the profile could be divided into four layers. In rainy year, the variance coefficient of soil water decreased first, increased later, and decreased lastly with the increase of soil depth, due to the continual rainfall infiltration and intensive evapotranspiration. The variance coefficient at surface soil layer was obviously smaller in rainy year than in drought year. Compared with that in bare land, the soil water cycling in grassland was deeper in depth and greater in intensity, as well as higher in evapotranspiration. The temporal change of soil water mostly depended on rainfall and evapotranspiration, especially in surface soil layer, and the change of soil water lagged behind gradually from low to deep layers in the profile. Soil water storage had a seasonal change, and could be divided into three main periods, i. e., decreasing in spring, alternatively decreasing and increasing in summer and autumn, and relatively stable in winter. In drought year, soil water storage decreased, and infiltrated rainfall was all consumed by intensive evapotranspiration. In rainy year, soil water storage increased, but most infiltrated rainfall (more than 80%) was consumed by intensive evapotranspiration.