Film Covering of Rock Outcrops Improves Soil and Vegetation and Reduces Runoff and Sediment on Abandoned Karst Slopes

To address severe soil erosion and ecological restoration difficulties on abandoned karst sloping farmland, this study proposed and tested an innovative micro-topography modification strategy—film covering of rock outcrops. Field experiments were conducted on typical abandoned karst slopes with 20 standard runoff plots (10 covered, 10 uncovered). Compared with non-covered plots, film covering significantly improved soil properties: bulk density decreased by 6.6%, total porosity increased by 6.0%, non-capillary porosity by 29.6%, macro-aggregates (>2 mm) by 11.6%, soil organic carbon by 14.5%, and volumetric water content by 26.0%. Vegetation also benefited: aboveground biomass increased by 39.9%, root biomass by 45.3%, vegetation coverage by 12.2%, and root vertical pullout resistance by 29.7%. Consequently, surface runoff depth was reduced by 23.9% and sediment concentration by 24.8%. Correlation analysis revealed significant correlations between soil–vegetation indicators and runoff/sediment yield. Specifically, runoff depth was closely linked to bulk density and total porosity, while sediment concentration correlated strongly with total porosity, root pullout resistance, aboveground/root biomass, capillary porosity, and bulk density. This study confirms that film covering of rock outcrops improves soil–vegetation conditions at the microscale and effectively reduces runoff and sediment generation.