Spatial Heterogeneity of Soil Thickness and Factors Controlling It in a Karst Basin

Soil is a fundamental component to an ecological system. This study is aimed to clarify the spatial heterogeneity of soils in the Houzhai River basin and the factors controlling it. Overall, 2755 sites designed using ArcGIS were studied; soil thickness, vegetation, land use (human disturbance), and topographic characteristics were analyzed. Soils in the basin are characterized by the high spatial heterogeneity. Soils on the elevated convex elements of topography are thinner than those in the depressions and on flat lands. Soils in the western part of the Houzhai River basin are generally thicker than soils in the eastern part of the basin. The mean soil thickness of forestland, paddy fields, arid land, and grassland is 37.40, 84.43, 69.08 and 56.03 cm, respectively. Based on the present study, soil thickness in the Houzhai River basin is closely associated with landscape, land use, and vegetation. It is interesting that soils of croplands, including paddy fields and arid lands, are generally thicker than soils of other land uses under similar environmental conditions. The major reason for this—either the choice of soils with initially greater thickness for cropland or the result of soil protection measures by land owners—remains open to arguments and needs to be clarified.