Abstract:

To provide a basis for the effective utilization of soil nutrients and agricultural management, the spatial variation rule of topsoil nutrients and its correlation with topographic factors were studied. The authors took Yanhe River Basin as the research object, the spatial distribution and variation of soil nutrients were studied by geostatistics and GIS. Based on DEM data, relevant topographic factors were extracted to analyze the influence of topographic factors on soil nutrient spatial distribution in watershed scale. The results show that the total nitrogen and organic matter in the topsoil of the study area are at a low level, the available potassium and available phosphorus are at medium level, and the pH is weakly alkaline. The spatial variation is in the following order: available potassium > available phosphorus > total nitrogen > organic matter >pH. The determination coefficients of the semi-variance function on soil nutrients are all more than 0.6, the spatial distribution of soil pH is the most fragmented, which are mainly influenced by structural factors. The nugget coefficient of soil available potassium and pH is less than 25%. With the influence of structural and random factors, soil total nitrogen, available phosphorus and organic matter have medium level of nugget effect. And the nugget coefficient of available phosphorus is the highest, indicating that human activities have greater influence on its spatial variation. The distribution of total nitrogen and organic matter increases first and then decreases from northwest to southeast. The distribution pattern of available potassium shows a wave of decreasing from northwest to southeast. The overall distribution trend of available phosphorus is reduced from middle to the upstream and downstream. The trend of pH change along a certain direction is not obvious. The correlation between soil nutrient spatial variation and topographic factors is consistent. In the region of low and flat terrain, the soil nutrients are more abundant, which is conducive to agricultural production. And the nutrient content is relatively low in the areas with large topographic relief at high altitude.

Key words: geostatistics, topsoil nutrients, spatial variation, topographic factors, Yanhe River Basin