Spatial Variance of Soil Organic Matter and Total Nitrogen in Pinggu of Beijing

1 076 soil samples were collected from Pinggu county of Beijing and analyzed for concentrations of soil organic matter(SOM) and total nitrogen(TN) in topsoil(0～20 cm) and subsoil(20～40 cm)respectively.The statistical results indicate that the mean values of SOM and TN are higher level in two soil layers and their coefficients of variation belonged to the middle degree.The contents of SOM and TN topsoil are higher than in subsoil.The result of semivariance analysis show that topsoil SOM and subsoil TN fitted for spherical model,and topsoil TN and subsoil SOM are described by exponential model.In topsoil,SOM and TN content have the smaller spatial correlation distance,which are 18.32 and 19.0 km,respectively.However,the SOM and TN content in subsoil have a large spatial correlation distance,which are 131.9 and 51.0 km,respectively.The spatial variance is mainly induced by structural factors.The Kriging method is applied to calculate the unobserved points and is used to generate the contour map.SOM and TN contents show the same distributed patterns,which decline from east-north to west-south.And their spatial distribution is affected by topology,soil type,fertilization and land use types.