Variability and driving factors of the soil saturated hydraulic conductivity along the horizontal and vertical directions in the upper catchment of Benggang

Benggang is a unique soil erosion landform in the subtropical hilly granite area of South China that seriously endangers the local ecology and environment. In this study, a developing Benggang in South China was selected to explore the spatial variability and the driving factors of the soil saturated hydraulic conductivity (Ks). The results demonstrated that the soil properties of Benggang landforms varied with the soil layer depth and slope position. Only the sand content increased with decreasing distance from the collapsing wall, while the soil organic matter (SOM) content, free iron oxide (Fed) content and cation exchange capacity (CEC) exhibited the opposite trend. Particularly, these parameters exhibited the most significant variation between the middle slope (MS) and lower slope (LS) I and II positions. The Ks values at the LS positions were significantly higher than those at the upper slope (US) and middle slope (MS) positions, and the Ks values first decreased and then increased as the soil layer depth increased. Among the slope positions, the variation in Ks values followed the order of LS II > LS I > US > MS. The Ks values in different directions exhibited notable multifractal characteristics, and the heterogeneity was stronger in the vertical direction than in the horizontal direction. The soil Ks values significantly differed between the different directions at four slope positions, and the values along the vertical direction were higher than those along the horizontal direction at the US and MS sites. However, the values along the horizontal direction were higher than those along the vertical direction at the LS I and LS II sites. Especially at the LS II site, the difference in the soil Ks values between the two directions was extremely significant (P < 0.01). The correlation coefficient values between Ks and the number, area ratio and mean volume of soil macropores were > 0.8. Path analysis revealed that the mean volume of macropores was the main factor affecting the Ks variation. The difference in the soil Ks values at the LS positions could effectively explain the mechanism of headward erosion on the Benggang slope. This study provides a theoretical basis for Benggang erosion control and the prevention of soil erosion in South China.