Spatial distribution characteristics of soil thickness and soil nutrient content in karst slopes

Grikes and cutters are common karst features in karst slopes which leading to high spatial heterogeneities of soil-rock structures. However, there is still lack of knowledge on spatial patterns of both soil types and related soil physical and chemical properties which in turn affected the rational planning and efficient use of limited water and soil resources in karst areas. In this study, 12 trenches (perpendicular to contour lines with a length of 24m and a width of 1m) were dug from downslope to upslope direction in a karst slope. The trenches were divided into three groups namely shallow soil type, middle soil type, and deep soil type according to their soil-rock structure and soil thickness. A typical trench was selected from each groups to investigate the spatial patterns of both soil thickness distribution and the main soil nutrients. The results are as follows.Soil thickness in karst slopes showed a high spatial variability ranging from 0 to 430 cm with the variation coefficient between 12.0% and 85.3%. The soil fertility was generally low, and the comprehensive fertility coefficient gradually decreased with the increase of soil depth. The soil fertility level of the 0-10 cm depth was relatively high, in contrast to the extremely poor soil fertility level below 10 cm. It is indicated that the soil nutrients mainly concentrate at the surface soil layer. Among all of those soil fertility index, total nitrogen, total phosphorus, and available potassium were significantly negatively correlated with soil depth. This study accumulated detailed field survey data for deepening the knowledge of soil properties spatial patterns and soil formation processes in karst hillslopes. The results can provide a theoretical basis for the improvement of the ecological service function and the optimal layout of land resources in the karst area.