| Based on geostatistics and geographic information system (GIS), the characteristics of spatial variability of soil organic matter. pH. cation exchange capacity and slowly available potassium of cultivated land in Tong-an county were quantitatively described by semi-variogram. On the base of the best semi-variogram, the maps illustrating four soil chemistry properties in studied area were made by interpolators and deterministic interpolators, then the effects of different interpolation methods were analyzed and compared, and the last distribution maps of four soil chemistry properties were generated by the optimal spatial interpolation method. The objective of study was to estimate spatial heterogeneity law of four soil chemistry properties and provided the scientific direction for soil amelioration and utilization, fertilizer application in Tong-an county. The main results were as follows:The average values of organic matter, pH, cation exchange capacity and slowly available potassium were 15.96g/kg, 5.85,4.55cmol(+)/kg, 177.19mg/kg respectively, it indicated that organic matter content in studied area was in a medium level, the soil was mostly acidic, the capacity of nutrient preserving and supplying and potassium potential supplying basically belonged to a low level. In addition, the coefficients of variability of all the chemistry properties belonged to middle intensity. The coefficient of variability of pH was lowest, while slowly available potassium was highest. The organic matter, pH and cation exchange capacity were normal distribution, while slowly available potassium was lognormal distribution, this indicated that the studied properties satisfied geostatistical requirement.The semi-variograms of soil organic matter, pH, cation exchange capacity in cultivated land were best described by exponential model, expect for that of slowly available potassium which was best fitted by spherical model. The definitive coefficients (R2) of four chemistry properties ranged from 0.729 to 0.961, and their nuggets were positive and ranged from 0.15 to 17.88. Nugget/sill of organic matter and slowly available potassium were 36.3% and 39.1% respectively, this showed that their spatial variability was mainly produced by structural factor, while that of pH and cation exchange capacity was primarily caused by random factor, because their nugget/sill were 49.9% and 50%. The results also indicated that the spatial correlation of four chemistry properties was moderately dependent. In addition, the correlation distances of four chemistry properties were different. The range of slowly available potassium was just 3480m, which showed that its spatial variability was great, the ranges of pH, cation exchange capacity and organic matter were 10650m,48840m, and 97800m respectively, which showed that they were spatially homogeneous comparatively.
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