The Comprehensive Evaluation And Research On Spatial Variability About Soil Fertility In Chengdu Plain

The soil fertility criteria and evalution methods were sleected to evaluate the soil quality in Chengdu plain and the changement of soil nutrient was analysised quantitively based on Markov chain principle. Spatial variability of soil fertility quality and its component at different scale and different direction have been stuied quantitively by the combination method of GIS and geostatistics to discover the principle of soil properties' distribution at regional scale.The results of soil qualiy evaluation show that: soil quality was well at most regions. In the past 20 years the nutrients' content have increased at different intensity. Total nitrogen increased 3.6%, total potassium increased 2.8%, available nitrogen increased 28.0%, available phosphorus increased 19.6%, available potassium increased 6.0%. But some physical and chemical properties that determined nutrients' availability are degrading in some region. The ratio of pH<5.5 and <6.5 increased from 3.8% and 31.2% to 11.2% and 60.5%, soil bulk density decreased 18.5%, soil microaggregate decreased 13.3%.The results of geostatistical analysis show that: the semivarigram for pH and the logarithm conversion value of physical clay, available phosphorus (P), microaggregate, CEC well fitted by spherical model. The semivarigram for soil organic matter, soil bulk density and the logarithm conversion value of total nitrogen (N), available nitrogen, available potassium (K), total potassium well fitted by exponential model. The spatial heterogeneity soil organic matter and CEC are relatively simple in small range, but physical factors and pH vary strongly in small range. The significant variance about semivariance for pH, soil organic matter, physical clay, total potassium, available phosphorus, and available potassium indicate these factors were controled by some important process at different scale. The spatial variability of soil organic matter, available potassium, and total potassium were produced by random factors. The spatial variability of physical clay, available nitrogen, available phosphorus, total nitrogen, pH, soil bulk density, microaggregate were produced by structural factors. All soil properties were in anisotropy through the whole research range. The spatial variability of available nitrogen, soil bulk density, available phosphorus, available potassium, total potassium, CEC focused on 0. The spatial variability of total nitrogen, soil bulkdensity, physical clay focused on 45. The spatial variability of soil organic matter focused on 90. The spatial variability of pH focused on 135. Every soil property exhibited the disffrent isotropic range of physical clay, available nitrogen, available phosphorus, total potassium, total nitrogen, pH were wide, and which of soil organic matter, microaggregate, available potassium, soil bulk density, CEC were narrow. With isotropy the fractal dimension of soil organic matter was highest; respectively the ratio of nugget to sill was highest to 38.2%. The fractal dimension of soil bulk density was lowest; respectively the ratio of nugget to sill was lowest to 0.01%. With anisotropy the difference between fractal dimensions at every way of pH was most significantly. The difference between fractal dimensions at every direction of microaggregate was least significantly. The puctual Kriging that was used to optimal linear estimate the soil properties can show the distribution of soil properties accurately.