An Approach to the Changes of Black Soil Quality(IV)——Spatial Variability of Soil Fertility Indices in Gongzhuling

Geographical information system(GIS) combined with Geostatistics was applied to reveal the spatial variability of soil fertility indices including soil pH,organic matter,available P,available K and clay in the topsoil(0~20cm) in Gongzhuling Area.The results showed that theoretical semivariogram models of soil pH?organic matter?available K?clay were best described with a spherical model,whereas the available P was best fitted with a pure nugget effect model.The ratios of nugget to sill of clay,available K,organic matter,pH were from 37.27% to 49.66%,indicating that the spatial correlation of the four fertility indices was moderately spatially dependent,and the spatial variability was affected by structural and random factors together.Based on the current criteria of classification,the soil pH and organic matter were mainly distributed in the grade of 2~3,and the available P and available K were in the grade of 2~4,whereas clay was in the grade of 3~4,which showed that the fertility indices in this region were in medium grades.