Effects of rainfall intensity and underground pore density on the soil erosion mechanism of sloping maize farmland in a typical karst area of SW China

The rainfall intensity, slope, and underground pore density are major factors affecting the soil erosion of maize-covered karst slopes. We studied the erosion process of maize-covered karst slopes and the influencing mechanism of soil erosion on these slopes under different rainfall intensities, slopes, and underground pore density via simulated rainfall tests. The results are as follows: (1) No runoff was observed on the slope surface under light rainfall (30 mm hr(-1)); instead, subsurface flow was predominant. However, runoff from the surface and subsurface flows under moderate rainfall (60 mm hr(-1)) increased with the rainfall intensity. The average surface runoff under extreme rainfall (90 mm hr(-1)) was 2.3-times that under moderate rainfall. In addition, the average subsurface runoff under extreme rainfall was 1.6- and 3.5-times that under moderate rainfall and light rainfall, respectively. The total amounts of surface and subsurface soil losses increased as the rainfall intensity increased. The surface and subsurface soil losses from light to moderate and extreme rainfall events increased by 258% and 151%, respectively. The soil loss from the surface was 5.3-times greater than that from the subsurface, indicating that the erosion of maize-covered karst slopes mainly occurs on the surface and that the subsurface loss is relatively small. (2) As the slope angle increased, the runoff, sediment yield, and proportion of erosion on the surface increased, and vice versa. (3) The subsurface runoff and sediment yield increased as the underground pore density increased, while the opposite occurred on the surface. Multiple regression analysis showed that the rainfall intensity is the most critical factor affecting the soil erosion of maize -covered slopes in karst areas, followed by the slope, while the influence of the underground pore density is small.