GIS-BASED SOIL LOSS ESTIMATION WITH USLE FOR SOIL CONSERVATION PLANNING IN HILLY AREAS OF PURPLISH SOILS

Estimating soil loss quantitatively and spatially is essential for identifying high erosion risk areas, and is helping to adapt soil conservation measures to specific sites. Because soil loss estimation is time-consuming and costly, using physical models on a regional scale, the Universal Soil Loss Equation (USLE), and integrating with a geographic information system (GIS), was applied in this study, making soil loss estimation and its spatial distribution feasible with reasonable costs and greater accuracy. A case study was conducted in the Jieliucun watershed as a representative of hilly areas of purplish soils in China. Rainfall data, a soil map, DEM, and a land use and land cover (LULC) map were used as primary data, and then USLE factors were generated by given methods. To investigate the relationship between predicted soil loss and environmental factors, the values of soil loss were also divided into a number of categories according to soil loss classes, slope zones, LULC types and soil types. Average of annual soil loss was 8.52 t ha(-1) yr(-1) for the whole watershed. More than 20% of the watershed fell into the soil loss classes over very low where average annual soil loss was more than the soil loss tolerance (7) value. The highest values were found in dry croplands with a slope between 15 degrees and 25 degrees as well as the purplish soils. In con-clusion, there is a strong need for adopting effective and affordable soil conservation measures to avoid an irrever-sible state of soil degradation in these areas.