Zhang XingYi;Sui YueYu;Zhang XuDong;Meng Kai;Herbert S J

;Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin 150081, China.

arable soils;black soils;nitrogen;nutrient availability;phosphorus;potassium;soil fertility;soil organic matter;soil parent materials;soil structure;soil surveys;soil types;spatial variation;statistical analysis;terrain;vertisols;water table

A total of 1400 soil samples from the plough layer (0-20 cm) at an approximate interval of 5 km were collected in the autumn of 2002 over the entire black soil arable crops region of Northeast China to determine the spatial variability of seven variables, such as total organic matter content (OMC), total N, total P, total K, alkali-dissolvable N (AN), available P (AP) and available K (AK). Classical statistics and geostatistical analysis was performed across the entire black soil area in Northeast China. In non-sampled areas ordinary kriging was utilized for interpolation of estimated nutrient determinations. Classical statistics revealed highly significant (P<=0.01) correlations with all seven of the soil properties, except for OMC with AP and total K with AK. In addition, using coefficients of variation, all soil properties, except for total K, were moderately variable. A geostatistical analysis indicated that structural factors, such as parent material, terrain, and water table, were the main causes of the spatial correlations. Strong spatial correlations were noted with OMC, total N, total P, AN, and AP, while they were moderate for total K and AK. The effective spatial autocorrelation of OMC, total N, total P, and AN ranged from 1037 to 1353 km, whereas the ranges of total K, AP, and AK were only from 6 to 138 km. The fit of the experimental semi-variograms to the theoretical models indicated that except for AN, kriging could successfully interpolate other six variables. Thus, the geostatistical method used on a large scale could accurately evaluate the spatial variability of most black soil nutrient properties in Northeast China..