Effect of Rock Film Mulching on Preferential Flow at Rock–Soil Interfaces in Rocky Karst Areas

Preferential flow is the most common form of water loss occurring at the interface between rock and soil (hereinafter referred to as “rock–soil interface”) in karst areas, and it is also one of the important factors causing soil water leakage into the underground. Therefore, it is of great significance to cut off the pathway of soil water loss through control of preferential flow. In this experiment, rock film mulching (RFM) was used to control the preferential flow at the rock–soil interface, and its influence on the soil water infiltration pattern and soil water content was analyzed by simulating rainfall, dye tracer tests, and digging soil profiles. The results show that: (1) the RFM can significantly control the soil water loss at the rock–soil interface, (2) so that the water intercepted by the above-ground rocks changed from longitudinal infiltration to transverse diffusion, more water moved into the surrounding soil patches, and (3) the soil water content was significantly increased. These results indicate that the RFM has an important blocking effect on preferential flow at the rock–soil interface, which has important guiding significance for reducing soil water erosion in karst areas.