Responses of soil aggregate stability and soil erosion resistance to different bedrock strata dip and land use types in the karst trough valley of Southwest China

Soil aggregate stability is an important index that reflects soil quality and anti-erosion ability and strongly affects soil processes and functions. Bedrock strata dips (dip and anti-dip slopes) and land use types primarily influence soil aggregate stability, whereas the detailed mechanisms are unclear in karst trough valley. Therefore, to explore the effects of bedrock strata dip and land use type on soil aggregate stability in karst trough valleys, soils were collected from five major land use types (abandoned land, grassland, pepper fields, corn fields and forest) on dip and anti-dip slopes. The soil was fractionated into macroaggregates and microaggrates using dry and wet sieving analysis. The soil particle size distributions in the macroaggregates and microaggregates were measured in conventional laboratories. The results showed significant differences in soil aggregate stability among different bedrock strata dips, slope positions, and land use types (P < 0.05). The variation ranges of macroaggregates and microaggregates in the pepper fields of the dip slope were higher than those on the anti-dip slope. Comparing all land use types, the forest of the anti-dip slope had >0.25 mm water-stable aggregates (85.31%) and mean weight diameter (2.67 mm) on the upper slope compared to that in the other slope positions of the dip slope. In addition, the dip slope had a higher percentage of aggregate destruction (35.57%) than the anti-dip slope (29.81%), and the soil erodibility factor value of the natural forest of the dip/anti-dip slope was significantly lower than that of the other land use types (P < 0.05). When the content of large macroaggregates was larger, the soil macroaggregate weight was greater. When the failure rate of the soil aggregates was lower, the stability of the soil structure was better. Overall, these results suggest that natural forests can significantly improve the stability of soil aggregates, thereby improving soil erosion resistance. Therefore, natural recovery measures should be implemented on dip/anti-dip slopes of karst trough valleys.