THE EFFECT OF SOIL WATER EROSION ABOUT CONVERSION OF CROPLAND TO FOREST ON THE LOESS HILLY REGION-TAKING WUQI COUNTY AS AN EXAMPLE

Conversion of cropland to forest for the quantitative evaluation of soil and water conservation benefits to the country retreat with typical county also forest engineering construction as the research object,based on 3S technology RUSLE soil erosion model,analyze and evaluate the time and space the county returning farmland to forest soil erosion changes. The results show that: Wuqi County Returning Farmland to Forest for 10 years,the effect of soil erosion control,a higher intensity of soil erosion land area in the substantial reduction. ① returning farmland to forest soil erosion distribution up to moderate erosion,the area accounted for 43. 62% of the total land area of Wuqi County,returning farmland before the soil erosion mainly to pole strength erosion accounted Wuqi County total land area of 42. 76% the county average soil erosion in ② returning farmland to 5 285 t /( km2·a) belong to the intensity of erosion,the average soil erosion on its returning farmland to 9 779 t /( km2·a) 1. 85 times after returning farmland to forest 17. 04 million tons( 3) of the study area,returning farmland to forest county per year to reduce the amount of soil erosion unused average soil erosion modulus of 19 513 t /( km2·a),the steep upland soil erosion modulus 12 449t /( km2·a) its erosion modulus were equivalent to returning arable land average soil erosion modulus 2 458 t /( km2·a) 7. 94 times and 5. 06 times( 4) of the study area also needs to strengthen the moderate erosion area of governance to be more effective to control soil erosion in the region.