GAO Junliang, GAO Yong, LUO Fengmin, DANG Xiaohong, FENG Wei, MENG Zhongju
To illustrate the effect of wind erosion on the grain size characteristics of the surface soil, five different land use types of Mu Us sandy land were chosen by a space-time substitution method. The soil mechanical composition and fractal dimension of top soil (0-1, 1-2, 2-3, 3-4, 4-5 cm) were analyzed through field sampling and laboratory experiments. The results show that the mass fraction of fine sand was the highest compared with that of other types of sand, and the mass fraction of coarse sand was the lowest among the five sample plots. The mass fraction of soil grains with different size fraction was in the following order: fine sand, middle sand, extremely fine sand+ silt sand, coarse sand, indicating fine sand is the main element in soil matrix composition in the studied area, and the sand has good sorting. The mass fraction of coarse sand and middle sand from high to low at different sampling depths was in the following order: 0-1, 1-2, 2-3, 3-4, 4-5 cm. The mass fraction of fine sand did not have significant difference at different sampling depths (P=0.4558), but the minimum content of it appeared at 0-1 cm. The mass fraction of extremely fine sand + silt sand at 0-1 cm and 1-2 cm was significantly lower than that at the other three layers (P=0.0126). It indicates that the evolution process from grasslands to sand dunes is a wind erosion desertification process, and the mass fraction of extremely fine sand + silt sand has been reduced. There was a highly significantly positive correlation between the fractal dimension and the mass fraction of the extremely fine sand + silt sand (P<0.0001). The fractal dimension of the five sampling plots has highly significant differences (P< 0.0001), and the order is the grassland (2.579), the newly cultivated land (2.479), 7-8 a farmland (2.361), >20 a farmland (2.100), and sand dune (1.716). Therefore, the fractal dimension could replace the soil mechanical composition to represent the degree of land desertification.