The spatial heterogeneity of soil nutrients in a mid-subtropical Castanopsis kawakamii natural forest

The spatial heterogeneity of soil nutrients and soil pH in Castanopsis kawakamii natural forest of Sanming City, Fujian Province was studied by the method of Geostatistics coupled with Geographical Information System (GIS) technique. The experimental results showed that pH had a weak variation, and the soil nutrients exhibited medium spatial variability. The variation intensity of soil nutrients and soil pH ranked from high to low as follows: available phosphorous (43.54%), available potassium (32.84%), hydrolyzable nitrogen (31.03%), total nitrogen (29.41%), total potassium (25.25%), total phosphorous (22.14%), pH (3.39%). In terms of different soil layers, the value of pH and total potassium raised with increase in soil depth, while total nitrogen, total phosphorous, hydrolyzable nitrogen, available phosphorous, available potassium reduced with increasing soil depth. Analysis of variance showed that soil nutrients and soil pH reached an extremely significant levels. Parameters of theoretical variogram models for soil nutrients and soil pH showed that pH, total potassium and available phosphorous fitted exponential model, total nitrogen fitted Gaussian model, total phosphorous and hydrolyzable nitrogen can be best described by spherical model and available potassium was well fitted by linear model. The effective ranges of total potassium and available potassium were 1806 m and 549 m, respectively, while the values for pH, total nitrogen, total phosphorous, hydrolyzable nitrogen and available phosphorous were 267 m, 130 m, 120 m, 182 m, and 117 m, respectively. In terms of spatial structure, pH, total nitrogen, total phosphorous, hydrolyzable nitrogen and available phosphorous showed high spatial autocorrelation, which was greatly affected by soil structural factors, such as stand structure, topography, microhabitat of forest gap and soil aggregate structure. Total potassium indicated moderate spatial autocorrelation, which was resulted from both soil structural factors and random factors. Available potassium indicated weak spatial autocorrelation. The spatial heterogeneity of available potassium was primarily affected by random factors, such as site preparation, change of land use, the rapid development of the ecotourism, the planning and construction of scenic areas. The spatial distributions of soil nutrients had different characteristics. Total nitrogen and total phosphorous were increased from south to north. The total potassium emerged circle distrib