Abstract:

Danjiangkou Reservoir Region is the water source area of the SouthtoNorth Water Transfer Project (Middle Route). Soil erosion is one of the major environment problems in this area. An indicator of soil susceptibility to erosion is referred as the soil erodibility factor K and it indicates vulnerability of soil to detachment and transport driven by raindrops and runoff. The soil erodibility factor K varies spatially according to variations of some soil properties on the surface. The objective of this study was to quantify the soil erodibility factor K and get some information 〖JP2〗necessary for conservation advice on how to prevent further soil erosion. The study was carried out in the Danjiangkou Reservoir Region with an area of in 6 486 km2 in the upper reach of the Han River basin, China. Soil classifications are often used to derive K factor value at the large scale. In this study, another method of calculating the K factor value in a large area with no soil classifications map was attempted. Firstly, a total of 198 topsoil samples (20 cm) were collected in August, 2009, and their locations were recorded using GPS. Soil mechanical composition was measured following the method put forward by Kettler in the laboratory. Soil organic carbon content of the samples were determined by the K2Cr2O7H2SO4 digestion method. Erosion/Productivity Impact Calculator (EPIC) model was used to calculate the soil erodibility factor K index value with soil property data obtained from the laboratory analysis. Then the soil erodibility factor K index value of the sampling sites was obtained. Secondly, the Ordinary Kriging interpolation module of the ARCGIS was applied to map K value in the study area. Then the K factor value was categorized into five classes. The results showed that the K value ranges between 0022 4~0046 8 t·hm2·h/hm2·MJ·mm, and the average K value was 0034 8 t·hm2·h/hm2·MJ·mm with a standard deviation of 0004 7, consistent with the estimates from previous studies in yellowbrown soil in China. There was certain spatial variation coefficient (CV) in the K value of the study area, but it was not too large (1351%). Most of the study areas (account for 9172%) belongs to medium susceptibility to erosion soil (0026 4<K<0046 1). The area of low K factor value (K≤0026 4) (difficult to erosion) accounts for 796％ and the area of high K factor value (K≥0046 1) (easy to erosion) only accounts for 033%. Spatially, there are greater values of K factor in the east than the west of the study area. Typically, there are larger K factor values in cultivated lands and they vary with cultural practices. Most of the west of the study area is covered with broadleaf forests and broadleaf and coniferous mixed forests with relatively high content of organic matter; while in the east, most of the land is cultivated field with low content of organic matter, and this leads to increase in soil erodibility. Accordingly, the east should be the key harnessment areas. The study will help prioritize critical areas for soil erosion prevention measures.