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High potential toxic element (PTE) concentrations in soils that exceed local regulatory threshold values have been reported in non-polluted mountainous areas worldwide. However, there have been few studies that have comprehensively investigated the contribution of natural factors including the parental material, pedogenesis processes and physiochemical properties of soils on the distribution of PTEs in these soils. Therefore, in this study, we studied the distribution of 13 PTEs in sloping farmland soils collected from a mountainous watershed in Guizhou Province, Southwest China. The contributions of natural influencing factors were analyzed using a geostatistical analysis and a geographic detector method. All of the PTEs were unevenly distributed, especially Sb, and the average contents of V, Cr, Co, Ni, Cu, Zn, As, Mo, Cd, Sb, Tl, Pb and Hg were 57.15, 36.20, 4.61, 12.61, 13.36, 63.50, 11.94, 0.78, 0.37, 6.44, 0.48, 27.42 and 0.36mg/kg, respectively. The proportion of samples with Cd, Hg and As exceeding the screening value of the soil pollution risk of agricultural land in China was 46.7%, 5.9% and 4.4%, respectively. Except for Cd and Pb, the q values of the PTEs calculated from the geographical detector were above 0.05, indicating that altitude changes, which affect the pedogenesis process, have a great impact on the spatial distribution. Stratigraphic factors contributed greatly to the distribution of Co, Ni and Cu, which indicates their similarity in parental material. The combined effect of clay content, topographic factors and agricultural land types had the strongest explanatory power for V, Cr, Mo and Pb. The distributions of As, Sb, Tl and Hg are strongly associated with a potential source of mercury ore, and their accumulation is also enhanced by the adsorption on soil clay. Agricultural As also contributes to its distribution. [ABSTRACT FROM AUTHOR]

Rocky desertification of karst in Southwest China has seriously influenced the normal life of local people. Soil erosion is the key process for inducing rocky desertification. This paper analyzes the stability and variation of shear strength under different of water contents of the brownish clay soil in carbonate rock area Chenqi of Puding in Guizhou province. Results show that the cracking of brownish clay soil aggregates occurs in the early soaked stage. The lower the initial water content of soil aggregates, the faster and more completely large particles disintegrate. Stability of soil aggregates is stronger with higher water content, but the entire shear strength decreases significantly; it will collapse entirely in the rainy season. Therefore, for desertification prevention and control in carbonate rock areas, greater attention should be given to effective protection measures during the rainy periods after long-term dry weather. The control during this period is essential in the whole process of desertification mitigation. [ABSTRACT FROM AUTHOR]