Spatial variations of soil organic carbon and nitrogen in peak-cluster depression areas of Karst Region

Classical statistics and geo-statistics were used to analyze the spatial variations of soil organic carbon (SOC), total nitrogen (TN) and C/N in three ecological areas of a peak-cluster depression with the Karst topography. The results show that SOC, TN and C/N increase with the succession level from artificial forest (I) to secondary forest (II), to primary forest (III). CV. of SOC, TN and C/N vary from 10.40% to 80.94% which show medium variations. Nugget/Sill of SOC and TN in I and III, and Nugget/Sill of C/N in I are less than 25%, which indicates there are high spatial autocorrelation. Nugget/Sill of SOC and TN and C/N in II, and Nugget/Sill of C/N in III are in the range of 32.6% and 41.7%, which implies the medium spatial autocorrelation. The distances of SOC, TN and C/N in I are longer than those in II and III. Kriged maps show that the spatial distribution of SOC is similar to that of TN in the three ecological areas. However, the spatial distribution of C/N seems irregular. There are sliced smooth distributions of SOC and TN in I and III, while there are fragmentized distributions of SOC, TN and C/N in II. The spatial distributions of SOC, TN and C/N are determined by the high heterogeneity of environment, and spatial heterogeneities in human badly disturbed I and non-disturbed III become lower than that in II.