关键词: 土壤全氮, 地统计学, 空间变异, Kriging

Abstract:

Nonpoint sources of nitrogen (N) in agricultural soils have been identified as one of the main causes of freshwater eutrophication. Studies have showed that decades of N fertilization at rates exceeding the amount removed by crops have resulted in widespread accumulation of N in agricultural soils in Taihu Lake basin, and the accumulation of N will increase the potential of soil N loss to surface and ground waters. Therefore studying the spatial variability of soil N at large scale will be helpful to develop optimal management practices for controlling agricultural nonpoint N pollution. Geostatistics has proven to be useful for characterizing and mapping spatial variability of soil properties. In this paper, a geostatistics method, combined with Geographic Information System (GIS), was applied to analyze the spatial variability of total soil N in topsoil in the typical area of Taihu Lake basin. The results showed that the spatial variability of total soil N was apparent in isotropy within the maximum lag extent of 40km, beyond which the anisotropy of spatial variability was increasing due to the change of soil parent materials in the direction of NE34°. The isotropic semivariograms showed that the ratio of nugget to sill of the total soil N was about 0.5,indicating that the total soil N had a relatively good spatial autocorrelation in the study area, and the range of autocorrelation extended to about 16km. The map of the total soil N interpolated through Block Kriging based on the fitted exponential model depicted that the soils in Jiangyin and Yixing counties generally had much more N than that in the other counties,which was mainly contributed to the different application levels of N fertilizers;and the "hot spots" of high soil N content were apparent in low-lying polderland, which probably was the results of interaction of topography and human factors such as fertilization.

Key words: total soil nitrogen, geostatistics, spatial variability, Kriging