Spatial variability of soil fertility quality indices in red soil region

Geographical information system(GIS)combined with geostatistics was applied to reveal the spatial variability of soil fertility quality indices including soil pH,organicmatter,available N,available P,available K,Total N,Total P and Total K in the topsoil(0-20 cm)of southeastern Hunan province.The results showed that theoretical semivariogram models of soil pH,available P,Total N and Total K were best described with an spherical model,whereas the organic matter,available N and available K were best fitted with a exponential model,Total P was best described with an gaussian model.The ratios of nugget to sill of available N and Total P were 13.6%,19.0%,respectively,indicating there existed strong spatial correlation.The ratios of nugget to sill of pH,organicmatter,available P,available K,Total N and Total K were 28.7%,29.9%,54.7%,53.1%,55.6%,73.0%,respectively,indicating a moderate spatial correlation.In the red soil region,the soil IFI(integrated fertility index) was closely related with parent material,based on which the fertility quality of the soil in north of Guanshanping village and south of Shulingsi village developed from limestone parent material belonged to theⅠ,Ⅱ and Ⅲ degree,which was high,the fertility quality of soil in Xingfuqiao village developed from slate parent material belonged to Ⅳ degree and the fertility quality of soil in south of Guanshanping village developed from quaternary red earth parent material belonged toⅤdegree.