中文摘要：

采用试验践踏与模拟降水控制试验，对16个不同试验组合样区表土（0～15cm）质地的机械组成进行分析，结果表明，随着践踏强度增加，土壤颗粒表现出不伺程度的粗化趋势，降水具有双向调节的作用。利用分形模型计算了土壤粒径分形维数，计算结果表明，分形维数指标与践踏强度呈负相关关系。但分形维数递减幅度与模拟降水处理水平相关，在模拟降水处理水平依次为干旱、自然降水、平水、丰水时，粒径分形维数递减幅度依次为4．33％，2．61％，1．34％和1．23％。降水与践踏的匹配关系，对形成确定的分形维数具有决定性作用。由于具有较高分形维数的土壤更易发生放牧侵蚀，若管理不善则会发展为荒漠化。因此，在此种意义上来说，土壤分形维数的测算对进一步研究放牧侵蚀机理和荒漠化形成过程可能具有推动作用。

英文摘要：

Soil particle size distributions in the 0-15 cm soil layer were analyzed in a two-factor （experimental trampling and simulated precipitation） controlled field experiment of 16 treatment combinations. The characteristics of soil particle size distributions were reflected in progressively coarser textured soils from low to high trampling intensities. Precipitation also regulates the process of soil particle size formation. The fractal dimension of soit particles were calculated using a fractal model and soil particle size distribution was negatively correlated with trampling intensity. However, reduced average fractal dimension size was related to precipitation. In a precipitation sequence of dry, natural precipitation, moderate rainfall, and abundant rainfall, the fractal dimension values declined in the sequence 4.33%, 2.61%, 1.34%, and 1.23 respectively. Fractal dimension values were determined by the interaction between precipitation and trampling. Because of high fractal dimension values, soils are susceptible to grazing-induced erosion, and could become desertified if not properly managed. Calculation of fractal dimension is a reliable indicator in monitoring grazing-induced erosion processes and predicting desertification. Therefore, soil fractal dimension measurement could be meaningful for evaluating grazing-induced erosion and the formation of desertification processes.