Spatial variability of soil properties and evaluation index for degradation in gold placer deposit mined land, Tibet plateau

To reveal the laws of spatial variability of soil properties and to find out the evaluation index for degradation degrees of soil in gold placer deposit mined land, the spatial variability of soil properties and the evaluation index for degradation degrees of soil in Segong gold placer deposit mined land in Ritu County, Tibet plateau were studied in the paper. The soil samples were collected from 0-40 cm surface layer, and after the field measurement and laboratory analysis, the methods of cluster analysis and principal component analysis were applied to study the soil variability and the evaluation index for soil degradation degrees, by using soft wares as SPSS and ARCVIEW. The results showed that: 1) the soil samples could be divided into four clusters, namely non-disturbance, slight disturbance, moderate disturbance and severe disturbance, corresponding to the four different soil degradation degrees, respectively. They were distributed as one concentric circle centered by the severe disturbance zone in the horizontal surface, whose boundaries could be identified clearly. And the closer to the inner circles, the more severely the soil deteriorated, and thus the greater the degradation degree was. 2) Soil gravel content, which was easily measured in field, was found to have significant correlation with other soil properties such as soil organic matter. Thus it was determined as the evaluation index for the soil degradation degrees. According to the gravel content, the classification criterion of various soil gradation degrees was identified as: the soil, whose gravel content 0, 45% belonged to non-degradation,（45%, 55% belonged to slight degradation,（55%～60% belonged to moderate degradation and （60%, 100% belonged to severe degradation. These results provide scientific basis for restoration and improvement of degraded soil in mined land.