[Soil nutrient distribution and its relations with topography in Huangshui River drainage basin]

By using GIS and geostatistic techniques, this paper studied the spatial distribution patterns of soil nutrients and their relationships with topographic factors in Huangshui River drainage basin, a water source of Danjiangkou Reservoir. In the study area, the soil total nitrogen, total phosphorus, and organic matter varied spatially at medium level, with the variation coefficients being 51%, 66%, and 85%, respectively, whereas the soil available phosphorus displayed a strong spatial variation, with the variation coefficient reached 161%. The soil total nitrogen and organic matter exhibited a spatially positive autocorrelation, while the soil total and available phosphorus presented a spatially weak autocorrelation. Altitude was one of the main topographic factors affecting the spatial distribution patterns of the soil nutrients, having significant effects on the spatial distribution of total nitrogen, total phosphorus, and organic matter. Slope and profile curvature also had significant effects on the spatial distribution of the soil total nitrogen and organic matter. Based on these, the regression prediction models of topographic factors and soil nutrient spatial distribution were established, and the digital mappings of the soil nutrients were made, which provided data support for the precise management of soil resources in the study area.