Spatial variability of soil organic matter in the upper stream of the Hunhe River basin, northeastern China

This study examined the spatial dependency of soil organic matter (SOM) at a county level in the upper stream of the Hunhe River basin, northeastern China, using geostatistics and geographic information system (GIS) techniques. The SOM contents in topsoil samples were collected at 219 locations in cropland and forest land of the upper stream of Hunhe River basin, which covers 53% of the total area of Qingyuan County. The SOM contents followed a normal distribution, with an arithmetic mean of 3.83% and median of 3.62%. Semivariograms showed that the SOM contents and the pH values had strong spatial dependency, which might be attributed to intrinsic and extrinsic factors. The pH values had stronger spatial dependency than the SOM contents, which suggested soil management practices had more intensive influence on the SOM contents. The experimental variogram of SOM has been fitted with an exponential model. The SOM contents were the highest under secondary forest and lowest under dry farmland. Map of SOM was generated through interpolation of measured values by ordinary kriging.