Soil structure and nutrient contents in underground fissures in a rock-mantled slope in the karst rocky desertification area

Abstract

Near-surface karst fissures are filled with soils. These soils are often derived from the erosion and transport of surface soil but have different properties than the surface soil in karst rocky desertification regions. This study was undertaken to determine the soil structure and nutrient contents in underground fissures with different grades of rocky desertification (no, potential, mild, moderate and severe). Based on field surveys, near-surface karst fissures were selected in a typical karst plateau area. Soil particle compositions, particularly nutrient characteristics, were determined through field sampling and laboratory experiments. The results indicated that the higher the rock desertification grade was, the higher the soil sand (0.02–2 mm) content and the lower the clay (< 0.002 mm) content. The soil in both limestone and dolomite fissures was basically neutral to weakly alkaline. The surface soil in dolomite fissures presented a higher soil organic matter content than that in limestone fissures, but the opposite was true for the subsurface soil. From the surface to the lower layer, the total nitrogen content generally decreased, and the total phosphorus content generally decreased in dolomite fissures but exhibited a more complex pattern in limestone fissures. The total phosphorus content of the surface soil was higher than that of the subsurface soil, but the total potassium content was lower. There was no significant difference among different soil layers. Near-surface fissures are a good place to promote vegetation restoration projects, because they provide good soil structure and nutritional conditions for plant growth.