Study On The Soil Erosion Control Benefit Of Converting Cropland To Forest For The Small Watershed In The Loss Plateau

Converting cropland to forest has been a basic measure in preventing soil and water losses, increasing water conservation function, improving the ecological environment of west China, and promoting the eco-economy sustainable development, and improving ecological environment effect is the key of converting cropland to forest. But there has been no few systematic quantitative studies about the soil erosion control benefit,which has affected assessment work of converting cropland to forest. The paper is a part of the project-the Land Use and Ecological Process, supported by the National Scientific Fund. The paper discussed the soil erosion control benefit of converting cropland to forest innovatively in Yangjuangou small watershed of Loess Hilly and Gully Region based on GIS, RS and GPS and USLE. The paper supplies scientific basis about assessment and research of the soil erosion control benefit of converting cropland to forest in Loss Plateau; the research of soil erosion rules supplies theoretical basis for water and soil conversation and the Planning of Forestry Eco-construction in Loss Plateau.The area of slope farmland was made up of 29.58% of total small watershed, arbor forest 10.18%, shrub land 0.19%,in 1984 before converting cropland to forest; while the area of slope farmland only was made of 0.12% of total small watershed, arbor forest 28.18%,shrub land 6.55% in 2006 after converting cropland to forest. The value of erosion force of rain fall was 1843.62 MJ mm/(hm2 h) before converting cropland to forest, while it was 1183.48 MJ mm/(hm2 h) after converting cropland to forest. The soil erosion was estimated, and the critical areas of soil erosion in the watershed were identified. Average soil erosion amount was 14801 t/km2 a in 1984 before conversing farmland to forest, which falls into the category of highest intention erosion. Highest intention category occupied percent 36.48% of the total watershed areas. Average soil erosion amount was 4116.7 t/km2 a in 2006 after conversing farmland to forest, which falls into the category of middle degree erosion. Slight erosion category occupied percent 28.97% of the total watershed areas; light erosion category, 23.10%. Highest intention erosion mainly distributed in sports and Liang Yuan slope of steep slope which has a gradient 20 to 25 degree. High erosion also distributed in the larger trenches , sleep slopes or bed surface with a gradient of 35 degree or higher where there was no vegetation. By 1984 compared with 2006 data derived through the implementation of soil erosion returning works to reduce soil erosion 21794.41t in the same time.Land use pattern had been changed greatly between pre- and post converting cropland to forest. The land use of single slope farmland in steep slope had been converted to comprehensive model, such as arbor forest and shrub land, shrub land and grassland, grassland, shrub land and terrace.The soil erosion control benefit of converting cropland to forest is obvious. The comprehensive model of combining arbor forest, shrub land, grassland and water to soil conversation engineering is used in preference in the converting cropland to forest project.