Impact of slope position on soil erodibility indicators in rolling hill regions of northeast China

The position of the rolling hill slope has considerable effects on soil properties and crop growth via the spatial heterogeneity of erosion intensity, which in turn probably impacts soil erodibility. However, few studies have been carried out to quantify the potential effects of slope position on soil erodibility indicators on long gentle slope. This study aimed to quantify the spatial variations in soil erodibility indicators of soil cohesion (Coh), saturated hydraulic conductivity (K-s), mean weigh diameter (MWD), mean number of drop impact (MND), soil penetration resistance (PR), soil structural stability index (SSI), soil erodibility of K factor, slaking rate (SR), organic matter content (SOC) and a comprehensive soil erodibility index (CSEI) on two typical rolling hill slopes in northeast China. Soil properties, root mass density (RMD) and litter mass density (LMD) were determined to explain the spatial change of soil erodibility indicators with slope position. The results showed that Coh, MWD, MND, PR and SOC declined from upper to middle, and then increased continuously until to lower position. The distinctly opposite changes were found in Ks and SR with slope position. No distinct variation was observed in K factor and SSI with slope position. For both two slopes, CSEI increased from upper to middle, and then decreased quickly to lower position. Compared to middle position, the mean reduces of two tested hillslopes were 51.72%, 14.74%, 24.28% and 72.52% for upper to lower positions, respectively. The results of Path analysis showed that SOM was the main factors contributing to the variation of CSEI with slope position. This study confirmed that the middle position is the most susceptible area to erosion on long gentle rolling hillslope. The results are helpful to understand the spatial variation in soil erosion intensity and design soil conservation measures on long gentle slopes.