Soil aggregates and fractal features under different land use types in a frequent debris flow area

The stability of soil aggregates and the fractal characteristics of four typical land use types (farmland, grassland, woodland, and bare land) in the Jiangjiagou Ravine (Yunnan, China), a frequent debris flow occurring area, were studied according to the normal mean mass diameter and fractal theory. The present research showed that the stability of the soil aggregates was different for the different land use types. When the soil depth was 0–30 cm, farmland soil formed more aggregates with diameters greater than 0.25 mm, i.e., the farmland soil was more stable than that of the other three land uses. When the soil depth was 30–45 cm, the order of stability of the soil aggregates was woodland > grassland > farmland > bare land. The fractal dimensions had a significant linear positive correlation with the amount of soil particles with diameters of <0.25 mm, and a significant negative linear correlation with the amount of soil particles with diameters of 0.25–0.5 mm, 0.5–1 mm and 1–2 mm. Smaller fractal dimensions of the soil particles correlated with more stable soil aggregates. The fractal dimensions had a positive linear correlation with the soil bulk density and a negative correlation with the concentration of organic matter. These results showed that soil aggregates can be used as a parameter for characterizing the soil structures and properties. According to these results, the soil particle fractal dimensions could not only objectively characterize the stability of the soil structure but also could be used to indicate soil structure and properties. In addition, these results have great significance for the discussion of the comprehensive evaluation of soil.