Comparison of Kriging interpolation precisions in different topographical units and number of samples:a case study of spatial distribution of soil total nitrogen in the Shucheng County

A total of 611 soil samples were taken from top soil(0～20cm deep) for examining the concentration of soil total nitrogen in Shucheng County,Anhui Province.Our objectives were to analyze the variation in the precision of Kriging interpolation in different topographical units and number of samples.Semivariograms of geostatistics indicate that the total soil nitrogen had a relatively good spatial autocorrelation in the study area.With the increasing sampling densities, the Normalized Root Mean Square Error(NRMSE) decreased,and precision of Kriging interpolation increased.Under the same sampling density,the accuracy of Kriging interpolation in the mountain area,hilly land,mound area and plain area increased orderly,indicating that the accuracy decreased with the increase in complicated degree of the topography.An analysis of the value of average development of the NRMSE shows that the growth of precision of Kriging interpolation differed significantly among four topographical units,with the highest value in the mountain area and the lowest in the plain.It can be concluded that topography and sampling densities are important factors affecting the accuracy of Kriging interpolation in large land areas.