表土粒度特征对风蚀荒漠化的响应

 为了阐明风蚀对表土粒度特征的影响，采用时空替代法选择毛乌素沙地5 种不同利用类型的土地（草地、新垦耕地、7~8 年耕地、>20 年耕地、沙丘），以其表层土壤（0~1、1~2、2~3、3~4、4~5 cm）为研究对象，通过野外实地采样和室内实验相结合的方法进行土壤机械组成与土壤颗粒分形分析。结果表明：1）5 个样地表层土壤机械组成均以细沙质量分数最高，为62.52%~80.40%，粗沙质量分数最低，仅为0.16%~0.43%，不同粒级土壤颗粒的质量分数高低排序为：细沙>中沙>极细沙+粉沙>粗沙，说明研究区土壤基质组成以细沙为主，沙物质分选好；2）5 个样地不同采样深度上的粗沙和中沙质量分数从大到小为0~1 cm>1~2 cm>2~3 cm>3~4 cm>4~5 cm；细沙质量分数各层次之间差异不显著（P=0.4558），以0~1 cm 层的质量分数最低；极细沙+粉沙的质量分数0~1 cm和1~2 cm层显著低于其他3层（P=0.0126），表明从草地到沙丘的演化是一个主要以极细沙+粉沙质量分数减少的风蚀荒漠化过程；3）土壤颗粒分形维数与极细沙+粉沙的质量分数呈极显著正相关关系，D=0.3661lnx+1.3409（P<0.0001）。5个样地的土壤颗粒分形维数存在极显著差异（P<0.0001），从大到小依次为：草地（2.579）、新垦耕地（2.479）、7~8年耕地（2.361）、>20年耕地（2.100）、沙丘（1.716）。因此认为土壤颗粒分形维数可替代土壤机械组成来表征土地风蚀荒漠化的程度。

Response of Surface Soil Grain Size Characteristics to Wind Erosion Desertification

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.