Spatial Variability Of The Concentrations Of Available N,P And K In Soil On County Scales

Soil is fundamental material basis of human survival and development. Analysis ofthe spatial variation of soil characteristics can reveal the distribution of soil nutrients inspace effectively, providing a scientific basis for soil nutrient management. County is thebasic unit of the state administration. Available nitrogen, phosphorus and potassium in soilhas a very good characterization for the evaluation of soil fertility, in the study of soilspatial variability. The study of spatial variability of available nitrogen, phosphorus andpotassium and its balance has practical significance for formulate scientific fertilizationplan, improving the nutrient resource utilization and promoting development of the formulafertilization by soil test.However, traditional agricultural production hasn’t taken into account this spatialchangeability. In the same area the same quantities of fertilizer was applied to the wholefield, so the application of nitrogen, phosphorus and potassium fertilizers is much inappropriate. This traditional farming patterns lack direction, easily leading to nutrientimbalances and low utilization rate of fertilizer.In order to manage soil nutrients, taking Gaoyang County of Hebei Province as astudy area, geostatistics combined with GIS was applied to analyze the spatial structural,spatial distribution of soil nutrients in topsoil (0-20cm) in this area; grid calculation wasapplied to evaluate the balance of available N, P and K. The Spatial distribution maps ofavailable N, P and K content in cropland soil were produced by means of the universalKriging interpolation, it objectively reflected the abundance or deficiency of nutrients inthis study area. The evaluation map of AN, AP and AK balance was produced by gridcalculation. Results were as follows:1. In all the survey region, the average content of soil AN, AP and AK were71.30mg/kg、17.79mg/kg and126.15mg/kg, respectively. The content of soil AN and AK havehigh levels, AK have low levels. The coefficient of variation (CV) of AN, AP and AK were28.27%,81.06%and47.31%, belonged to moderate variability. These three availablenutrients took on normal distributions, which met the prerequisite for the study of spatialvariability of soil.2. Use the application of GS+software to make semi-variance analysis of nutrientdata and to obtain the theoretical model of each kind of soil nutrient. The best theoretical model of soil AN and AP was the exponential model, the best theoretical model of AK waslinear model. The C0/(C+C0) of AN was less than25%, had strong spatial self-correlations,structural factors were the main factors which affected the spatial variability of available Ncontents, the ranges of spatial dependence were16.21km. The C0/(C+C0) of AP contentwas between25%～75%, had moderates spatial self-correlations, the spatial variabilitywas caused by structural factors and random factors, and the range of spatial dependencewas21.57km. The C0/(C+C0) of AK content was more than75%, had weak spatialself-correlations, the spatial variability was caused by random factors, and the range ofspatial dependence was22.40km.3. The integrative comparisons of kriging prediction errors were carried out to fit thebest trend effect, the0-order trend effect was preferable. The Spatial distribution maps ofavailable N, P and K content in cropland soil were produced by means of the universalKriging interpolation, classified the data according to the abundance and deficiency’s indexof the concentrations of available nutrients. The concentration of AN was medium or high.The concentration of AP was low, the areas were less than25mg/kg AP accounted for91%of all the areas. The soil contained rather high AK, spatial distribution had no significantcharacteristics.4. The grid calculation was made to get evaluation map of nutrient balance, finallyapplied to evaluate the balance of AN, AP and AK. The evaluation map of nutrient balanceshowed that the areas of very imbalance, imbalance and balance accounted for40.46%,38.81%and20.73%of all the areas of investigative regions respectively. Theconcentrations of available N, P and K were high or medium in the balance areas. Thereare three balance conditions in plain areas, spatial distribution had no significantcharacteristics.