Correlation degree analysis of soil fractal dimension and physical and chemical properties under different land use types in debris flow prone areas

In this study, we used Jiang Jia River as an example to comprehensively evaluate soil structural stability of different land use types. Cultivated land, grassland, forest land, and bare land were chosen as research materials. Based on fractal theory, the fractal characteristics of soil under different land use types were analyzed, the main influencing factors of soil structural stability were analyzed using the principal component analysis method, and the coupling model between fractal dimension and physical and chemical properties of soil was constructed by means of correlation coupling degree method. The results showed that the fractal dimension of soil under different land use types ranged from 2.71 to 2.75, and the soil particle content of 0.5～2 mm determined the fractal dimension of soil under different land use types. The fractal dimension of soil particles was significantly correlated with the content of alkaline nitrogen, bulk density, and organic matter in soil, and the physical and chemical properties and fractal dimension were moderately correlated. The effect of soil physical and chemical properties on the fractal dimension was bulk density > alkaline nitrogen > organic matter. The coupling degree between fractal dimension and physical and chemical indexes of soil was weak, and they did not reach the optimal state. The degree of system coupling coordination of different land use types was sorted by size as follows: forestland > grassland > cultivated land > bare land. It was beneficial to increase vegetation cover and decrease anthropogenic disturbance for the formation of stable soil structure. These findings can provide some theoretical basis for vegetation restoration and soil structure description in watersheds.