Study On The Geochemical Assessment Model Of Soil Quality

Since 1999, multi-objective investigation of geochemistry has made a great achievement and got a great deal of high quality geochemical data in China. Analyzing the entironment information contained in geochemical data can supply scientific basic for local agriculture development. This article based on the multi-objective geochemistry investigation data, evaluation index of the geochemical soil quality was determined firstly, then the fuzzy mathematics method was used to assess the soil texture, the fertility, the environment quality and pH; the IAHP was used to determine the weight of factors and soil quality was synthetically assessed integrating various single-factor appraisal result.In the factors that effect on the soil quality, there are direct or indirect relation between soil texture, soil fertility, soil environment quality, soil pH value and geochemical data. The quality of these factors are determined by clay minerals, organic content, large nutrient elements, trace nutrient elements, heavy metal element, atmospheric absorbed dose rate, pH and the contents of Se, F, I etc. Therefore, these factors are selected as assessment indexes.Soil texture is determined by the composition of variant size of solid particles and clay fractions mainly consist of clay mineral and colloid. Different clay minerals have a great difference in water-holding, fertility-holding and fertility-supplying capacity, thereby the mineral composition of soil and total clay are important factors which can affect soil texture.Oxides in soil exist as minerals or compounds. Except polymorphs, each mineral has particular composition of oxides. By testing 60 typical soil samples from Miluo-Xiangyin Area in Hunan, species of the mineral in soil are confirmed, based on mass balance between oxides components and mineral components, using the linear programming, contents of minerals in soil are confirmed utilizing oxides content. The results show that this method is more accurate, easy to achieve and has less influencing factors.The suitability of the soil mineral composition and the clay total quantity to the crops growth was measured by "appropriate" indicators. "Appropriate" means the range of make a better yield of a crop, above or below this range is not suitable the crops growth. "Appropriate" is a fuzzy concept, uses the membership degree describes "appropriate" degree, describes "appropriate" difference of intermediate values with the membership function. The membership function is measurement that has the certainly subjective factor to the fuzzy object. Membership function parameters should be determined by reference to the corresponding national standards; without the national standard, use the local as far as possible the high production, the high quality crops area target of statistic value to determine the parameter; difficult to identify high-yield and high-quality area, use the statistic value of the entire evaluation region of soil quality to determine membership function parameters could get good results.The fuzzy logic system is one of soil quality geochemistry appraisal effective methods. The system includes fuzzy generator, fuzzy inference machine and defuzzification. While the fuzzy inference machine is the core part of the system, the fuzzy inference is the computation process that refers assigns the input space to map through the fuzzy logic method to a specific output space. The process includes fuzzy logic computation, fuzzy implication and output aggregation.The suitability of the soil mineral composition quantity to the crops growth followed "limiting factors law" and the fuzzy logic system was established according to the law. First, the corresponding membership function to use of soil clay minerals into the input fuzzy sets. Secondly, the fuzzy logic operations using "and" Operation "minimal", obtained synthesized fuzzy sets. Thirdly, according to "If mineral composition 'appropriate', Then suitable the crops to grow" the principle, use "minimal" carries on fuzzy implication computation, obtains the conclusion fuzzy set. Finally, using "takes the minimum value from biggest membership set" carries on defuzzification computation. The soil mineral composition to crops growth being suitable membership degree could be obtained. According to the above membership degree and the clay total quantity, uses the similar method, obtains the soil texture to crops growth being suitable membership degree.This method avoids the problem of determining the weight factor and reduces the subjective factor during the evaluation process.The soil fertility appraisal of geochemistry index has the soil organic content, large nutrient elements, trace nutrient elements, and pH.When content of soil organic matter higher, the soil fertility is the better. Soil organic matter content indicators could be calculated using soil organic carbon content using a conversion factor of 1.724. The suitability of the soil nutrient elements to the crops growth should use "appropriate" indicators to measure,above or below this range will lower the yield and quality of crops. The soil pH influence nutrient elements effective content, too acid or too alkaline crops can be used to reduce the nutritional content. According to the state classification criteria to determine the organic matter, large nutrient elements and pH of membership function's parameters. The micro nutrient elements membership function parameter may use the soil average value to add or to reduce two time of standard difference multiplied by the K-value method. K value is the national soil mean value and soil average background value ratio.These indexes obey "limiting factors law", according to the above establishment and soil mineral composition same fuzzy logic system. And the membership degree of suitability of soil fertility and crop growth could be gotten.The soil heavy metal, the soil radioactive contamination and pH are affecting factors to the agricultural production output and quality. Se, F, I element and endemic disease is mutually related, Se, F and I may affect human health. Heavy metal and radioactive element content higher, pollution more serious, the agricultural product quality is worse; when soil pH is suitable, the crops are easy to survive and grow, the peracid or the peralkali would cause the crops death. According to the relation between radioactive element content of the soil and surface with one-meter height of the absorbed dose rate in air, the absorbed dose rate in air was calculated. Based on the entire area mean value, membership function parameter was obtained and radioactive pollution could be determined. According to the national standard, membership function parameters of the heavy metals and pH harm to the crop was determined.These factors obey "tolerance law", according to the above establishes the fuzzy logic system. First, transforms using the membership function various targets as the system input fuzzy set. Secondly, carries on the fuzzy logic operation, the use "or" in the operation "maximum" the law, obtains the synthesis the fuzzy set. Thirdly, according to "If pollution degree serious, Then agricultural product receives the harm bigger" the principle, use "minimal" carries on the fuzzy implication computation, obtains the conclusion fuzzy set. Finally, using "takes the minimum value from biggest membership set" carries on defuzzification computation. obtains the soil environment quality to crops harm membership degree, it and soil environment quality to crops advantageous membership mutually for complementary set.Se, F and I are the healthy environment quality index that may cause endemic disease. It is beneficial to human health when the contents of them are appropriate, while endemic diseases may be led by excessively high or low content. The membership function parameter may use the soil average background value to add or to reduce one time of standard difference multiplied by the K-value method. They satisfy "limiting factors law" to the human health, establishes the fuzzy logic system. Membership degree of human health could be gotten by the same fuzzy logic algorithm to soil mineral composition. The pH also affects the soil quality such as causticity. According to national grading standards, membership function is determined and the degree of membership is confirmed.According to various factors having different effect on soil quality, weight coefficients are confirmed by improved AHP. Improved AHP overcome the disadvantage that there are more factors in conventional AHP and make the calculation of weight coefficients and consistency check simpler.The geochemical fuzzy evaluation model of Soil quality is applied in Miluo-Xiangyin Area of Hunan and the satisfying effect was obtained. The result shows that the model can make the full use of the data of multi-objective geochemistry investigation and assess scientifically soil quality, so scientific suggestion could be put forward for the proper exploration of local land.