Fractal Features of Soil Particle Size Distributions and Their Implications for Indicating Enclosure Management in a Semiarid Grassland Ecosystem

Soil particle size distribution (PSD) is becoming an increasingly useful tool for the objective description of soil structure and intrinsic links between soil and the environment. Here we examined the fractal features of PSD and its correlation with soil physiochemical properties in grasslands under grazing and protected from grazing (enclosure) animals, before and after plant growing periods in a semiarid grassland ecosystem, in northern China. Our results showed that sand content was significantly higher in grassland soils under grazing compared with the enclosure at both sampling times (May and September), whereas their silt and clay contents followed the reverse pattern. The fractal dimensions of PSD (Dm) under enclosure were significantly greater than those found under grazing. The soil clay, silt contents and Dm were positively correlated with soil total N, total C, soil pH, and moisture content. By contrast, the soil sand content declined with increasing total N, total C, pH, and moisture content of soil. The soil fractal dimension of PSD had a positive correlation with soil clay and silt content, whereas it had a negatively correlated with sand content. From these results, we conclude installing enclosures can promote soil clay, silt, and soil particles' fractal dimension, with the latter could be used as a quantitative indicator of soil fertility characteristics. But it is unnecessary to use the fractal dimension of PSD as an index to evaluate the effects of enclosure management on degraded grassland.