Characteristics of soil gravel distribution in karst small watershed and its influencing factors

In order to explore the influencing factors, formation mechanism and distribution of karst soil gravel content, 3,180 soil samples were collected to analyze the distribution features of soil gravel contents influenced by different factors in the Houzhai river basin; and the method of correlation analysis was employed to determine the primary influencing factors. The results show that the slope, lithology, soil thickness and vegetation type are the main factors influencing the soil gravel contents, among which the slope has the greatest influence on the soil gravel content distribution in karst areas. Under the condition of different slopes, the changes of the soil gravel content are as follows: When slope < 30 °, soil gravel content increases with the slope. When the slope > 30 ° soil gravel content decrease with the slope. The results also show that soil gravel content decreases with the increase of soil thickness. The order of soil gravel content in different vegetation types is: shrub > herb > tree. Different lithologies can form soils, in which the order of soil gravel content is: dolomite > limestone > argillaceous limestone > quaternary yellow clay > sand shale. The lithology of karst area has a great impact on the weathering rate and gravel volume of the soil, which is the material source of soil gravel content. The slope is the driving factor to promote migration and redistribution of soil gravel content, while vegetation types and soil-bed thickness are the response factors.