| The shortage of soil and water resources and deteriorate of ecological environment has been a serious problem that has been of worldwide critical concern, Which make people realization that it is importance to saving water and protecting environment. To ensure the food safe and make the ecological environment good development, it should be enhanced the research on management of soil and water resources in farmland and reconstruction of ecological system. And dealt with the relationship between water resources use and ecological environment reconstruction, popularized the techniques of saving-water irrigation and the practice of skywater use. In accordance with the water resources, adjusting the dimension of agricultural industrialization structure, transforming the irrigation from traditional "sufficient water high yield" into "saving water increasing yield", to improve the yield efficiency of agricultural water use and actualize strategy of water resources sustainable use and ecological environment sustainable development.Soil erosion and arid agriculture are simultaneity existence in the areas on Loess Plateau, which make serious effect on agriculture production and ecological environment, and great increase the watercourse controlling and water resources availability difficulty. Hence, carrying on the transformation mechanism and affecting factor of rainfall, infiltration and runoff under different underlayer and planting crop in farmland of loess hilly areas. And quantificational simulating the processes of transformation, which can make clear the law of rainfall-infiltration-runoff, then hunting the measures and mechanism of artificial control, increasing infiltration and soil water holding, decreasing runoff and soil erosion, pertinently counterchecking soil and water losses. Especially in loess hilly areas where cannot irrigate the farmland and the only water resources is the precipitation, can supply the scientific foundation for reasonable harnessing the local skywater resources to develop agriculture and modifying ecological environment. In this paper, grounded on the research background as noted previously, complied with the features of loess area, based on a great deal of field and laboratories experiments with advanced instruments. The laws of hillslope water exchange under different underlayer surface and planting crop conditions have been further studied, and a numerical model has been presented to quantitatively describe the interrelation of rainfall-infiltration-runoff on hillslope. The main results are showed as follows: First, taken advantage of TDR, the soil water movement trends before and after rainfall, the soil water movement developments under different underlayer surface and evaporated condition in farmland, soil water movement during infiltration and soil water redistribution process after infiltration have been systematic observed in 1996 and 1997. Simultaneously, the amount of runoff and sediment in the plots under the rainfall have been measured, which can act as the important basis data for systematic research on the laws of water transformation in farmland under different underlayer surface of loess hilly areas. Second, the data of rainfall, infiltration and runoff in 1996 and in 1997 have been analyzed. The law of rainfall, infiltration, runoff in farmland under different underlayer surface condition of runoff, no runoff have been studied and systematic researched the soil water movement trends in farmland under the long-term without rainfall condition. Third, analyzed the law and affecting factor of runoff and sediment in the runoff plots and pointed out that the intensity of precipitation was the most main factor that affected the amount of runoff and sediment in the plots. And the time of precipitation, the covering, the slop, the length of slop and the initial soil water content in the plots are also affecting factor. Especially, the initial soil water content doesn't affect the amount of runoff and sediment in the plots but the starting time of runoff...
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