Vertical distribution of soil mechanical properties under different land use types in karst area

Soil erosion refers to a process that soil and soil parent materials are destroyed under the exogenic action. To understand impacts of land use type on soil mechanical properties and to provide scientific basis for soil erosion，the characteristic of distribution of soil mechanical properties at various soil depths (0-50 cm) under three land use types(woodland，shrub-grassland，slope cultivated land) at typical limestone site in Huaxi district in Guiyang city is researched by means of fields vegetation investigation，soil compaction and shear tests in this study. Guiyang city is located in east the slope of the Yunnan-Guizhou Plateau with well developed karst landform，and the soil types there are mainly yellow soil with sticky heavy- texture. In this study，slope cultivated land are bare slope land without crops，vegetation of shrub-grass land is dominated by Pyracantha fortuneana and ferns，vegetation woodland is dominated by Pinus massoniana. 30 sample plots are selected totally in the study including 10 plots of slope cultivated land，10 plots of shrub-grassland and 10 plots of woodland. Soil samples from 0-50 cm in depths with 10 cm for a layer that totaling in 5 layers are collected. It turns out that soil cohesion c increases along with depth，which significantly affected by land use types at 0-35 cm deep. The change of soil internal friction angle φ isn’t apparently different at 0-50 cm deep under different land use types and shows S-shaped on the whole，indicating that soil internal friction angle φ is affected by parent material. Soil compaction increases along with depth in different land use types，the soil compaction of the woodland and shrub-grassland are higher than slope cultivated land at 0-20 cm deep. The soil compaction，increasing with depth，in the shrub-grassland and the slope cultivated land has the same tend below 20 cm deep，which is higher than that in the woodland. Research shows the growth of vegetation can improve soil cohesion c and soil compaction. Therefore，protecting and recovering vegetation in karst area and changing land use of slope cultivated land are the main approaches to protect soil and control rocky desertification.