Establishment of the harmonious mechanism of water and soil to ensure the sustainable development of agriculture

The contradictions in water and soil resources and its impacts on agriculture in China are analysed，and the mechanisms of precipitation runoff,vegetation and waterenriching layers of soil in water detainment,and the functions of reservoirs in preserving and storing water also are dissected.The threshold value of water and soil loss,the mechanism of harmonizing the contradiction in water and soil,and the countermeasure of sustainable developmental agriculture are proposed.