How do Microtopography Act in the Pedogenic Characteristics of Mudstone-derived Soils in Hilly Mountainous Regions?

The topography is a critical factor that determines the characteristics of regional soil formation. Small-scale topographic changes are defined as microtopographies. As a characteristic topographic condition in hilly mountainous regions, the redistribution of water and soil materials caused by microtopography is the main factor affecting the spatial heterogeneity of soil and the utilization of land resources. In this study, the influence of microtopography on pedogenesis was investigated using soil samples formed from mudstones with lacustrine facies deposition in the middle of the Sichuan Basin and developed into hill landforms by erosion of flowing water. Soil profiles were sampled along the slopes at the summit, shoulder, backslope, footslope, and toeslope positions. The morphological, physiochemical, and geochemical attributes of profiles were analysed. The results showed that the soil thickness increased significantly with changes in the soil profile configuration from the summit to the toeslope, and the profile configuration changed from A-C to A-B-C. The migration direction of Ca and Na at the summit, backslope, and footslope changed from enrichment to leaching, whereas that of Al, Fe, and Mg changed from leaching to enrichment. At the summit and shoulder of the hillslope, weathered materials are transported away by gravity and surface erosion, and new rocks are often exposed; therefore, the characteristics of soil development is relatively weak. However, in flat areas such as the footslope and toeslope with sufficient water conditions, the long-term contact between water, soil, and sediment leads to further chemical weathering, resulting in highly developed characteristics. Microtopography can affect physicochemical properties, chemical weathering, and redistribution of water and materials, resulting in differences in pedogenic characteristics at different slope positions.