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The characteristics of soil water cycle and water balance on steep grassland under natural and simulated rainfall conditions in the Loess Plateau of China

Chen, Hongsong, Shao, Mingan, Li, Yuyuan
Journal of hydrology 2008 v.360 no.1-4 pp. 242-251
soil water content, soil water balance, grasslands, rain, rainfall simulation, hills, slope, loess, infiltration (hydrology), evapotranspiration, soil water storage, grassland soils, China
Large-scale vegetation restoration has been helpful to prevent serious soil erosion, but also has aggravated water scarcity and resulted in soil desiccation below a depth of 200cm in the Loess Plateau of China. To understand the dynamic mechanism of soil desiccation formation is very important for sustainable development of agriculture in the Loess Plateau. Based on natural and simulated rainfall, the characteristics of soil water cycle and water balance in the 0-400cm soil layer on a steep grassland hillslope in Changwu County of Shaanxi Loess Plateau were investigated from June to November in 2002, a drought year with annual rainfall of 460mm. It was similarly considered to represent a rainy year with annual rainfall of 850mm under simulated rainfall conditions. The results showed that the temporal variability of water contents would decrease in the upper 0-200cm soil layer with the increase in rainfall. The depth of soil affected by rainfall infiltration was 0-200cm in the drought year and 0-300cm in the rainy year. During the period of water consumption under natural conditions, the deepest layer of soil influenced by evapotranspiration (ET) rapidly reached a depth of 200cm on July 21, 2002, and soil water storage decreased by 48mm from the whole 0-200cm soil layer. However, during the same investigation period under simulated rainfall conditions, soil water storage in the 0-400cm soil layer increased by only 71mm, although the corresponding rainfall was about 640mm. The extra-simulated rainfall of 458mm from May 29 to August 10 did not result in the disappearance of soil desiccation in the 200-400cm deep soil layer. Most infiltrated rainwater retained in the top 0-200cm soil layer, and it was subsequently depleted by ET in the rainy season. Because very little water moved below the 200cm depth, there was desiccation in the deep soil layer in drought and normal rainfall years.