The purpose of comprehensive evaluation of agricultural geological environment quality is to reflect the overall situation and regional distribution of agricultural geological environment quality, provide geochemical basis for macro-management and planning of land at all levels in provinces and cities, and serve the sustainable use of land; At the same time, it plays a guiding role in adjusting agricultural planting structure, developing characteristic and high-quality agricultural products, promoting scientific and rational fertilization and soil pollution control. Therefore, the evaluation needs to comprehensively consider various elements of agricultural geological environment, including geological background, soil geochemistry, water geochemistry, safety and suitability of agricultural products and climate environment. Through multi-factor data integration, information mining and extraction, the key factors and index factors affecting agricultural geological environment quality and agricultural production are revealed.
Second, establish an evaluation system.
There are many models of comprehensive evaluation methods in agriculture, environment and ecology. The commonly used methods in the past include graphic superposition method, analytic hierarchy process, grey correlation method, comprehensive index method, expert system method, neural network method and so on. With the deepening of the national eco-geochemical investigation, China Geological Survey put forward the geochemical evaluation of land quality, and formulated the Technical Requirements for Geochemical Evaluation of Land Quality (Trial) (DD 2008-06). Based on the multi-objective regional geochemical investigation, according to the geochemical index factors such as land beneficial elements, toxic and harmful elements, organic pollutants and their effects on the basic production functions of land, The evaluation index mainly reflects the geochemical factors of land quality such as soil fertility index and soil environmental health index, supplemented by air quality, water quality and agricultural product safety, and comprehensively considers various factors related to land use to realize the geochemical evaluation of land quality.
In view of the gradual maturity of the theoretical basis, methods and technical experience of comprehensive evaluation of land quality geochemical evaluation, based on the data characteristics of this study, the comprehensive evaluation of land environmental quality was carried out in accordance with the Technical Requirements for Geochemical Evaluation of Land Quality (Trial), based on the comprehensive quality of soil (environmental quality and fertility quality), the comprehensive quality evaluation of shallow groundwater and the safety evaluation of regional agricultural products.
The first step, according to the technical requirements of evaluation, beneficial elements, harmful elements, pH value, organic matter and other internal indicators affecting land quality are screened out, which constitute the internal factors of comprehensive environmental quality of land. Taking every 4km2 as the evaluation unit, the participating indexes are weighted by AHP, the membership function value of the indexes is calculated by membership function model, and the comprehensive score (i.e. comprehensive index) is calculated by addition model. According to the comprehensive index value, the "color block diagram" of comprehensive evaluation of land environmental quality is made to realize the zoning of comprehensive evaluation of land environmental quality.
Secondly, shallow groundwater and crop quality are external indicators that indirectly reflect land quality. Shallow groundwater enters the soil through agricultural irrigation and drinking, which will cause changes in land quality, and crop safety indicators can indirectly reflect land quality. Based on the geochemical research results of shallow groundwater and agricultural products, the environmental quality of shallow groundwater and agricultural products is evaluated according to the water environmental quality standard, the classification standard of agricultural products' edible safety and the corresponding evaluation methods, and the external factors of land comprehensive environmental quality are constructed to realize the comprehensive evaluation and classification of land environmental quality.
Thirdly, the shallow groundwater and crop quality representing external factors are superimposed on the color blocks of the evaluation unit by mathematical representation to form a comprehensive evaluation map of land environmental quality, which comprehensively evaluates the land area, proportion, distribution range and management suggestions of each grade.
(a) Assessment of soil fertility
Soil nutrient elements can be divided into three categories according to their contents: ① Essential macroelements: N, P, K, S, Ca, Mg and organic matter. ② Essential trace elements: iron, manganese, zinc, copper, boron, molybdenum and chlorine. ③ beneficial elements: silicon, cobalt, nickel and sodium.
According to the screening principle of soil fertility indicators in Technical Requirements for Geochemical Evaluation of Land Quality (DD 2008-06), the above indicators were screened. Indicators with suitable areas and rich areas accounting for 80% ~ 90% of the total evaluation area do not participate in the evaluation, while indicators with poor correlation coefficient among multivariate statistical elements participate in the evaluation, and indicators with relatively small correlation distance (α) and relatively large C0/(C0+C) are selected to participate in the evaluation by using semi-variance function value. Finally, the comprehensive fertility evaluation indexes are determined as follows: essential elements of nitrogen, phosphorus, potassium and calcium, organic matter, essential trace elements of molybdenum, boron, manganese and zinc, and beneficial elements cobalt and silicon.
In the evaluation process, AHP (yaahp4.0 1 software) is used to give weight to the participating indicators (Table 4-4 1), and the membership function value (fi) of the indicators is calculated by using the membership function model.
Table 4-4 1 comprehensive fertility index weight assignment (Ci) results table
According to the above index screening, the weight threshold results and the membership function value calculation model, the weight and membership degree of the measured values of each evaluation index are calculated by using the addition model to obtain the comprehensive index of soil fertility;
P=∑fi×Ci(i= 1，2，3，4……，n) (4-5)
Among them: P is the comprehensive fertility index; Fi is the membership function value of the i-th evaluation index; Ci is the weight of the i-th evaluation index. According to the comprehensive index P of soil fertility, the comprehensive fertility is divided into three grades, and when P≥0.7 is the first grade, it is defined as the nutrition and beneficial elements rich area (high fertility area); 0.3 < P < 0.7 is the second grade, which is defined as the middle area of nutrition and beneficial elements (middle fertility area); P≤0.3 is the third grade, which is defined as partial nutrition and beneficial elements deficiency area (low fertility area).
(2) Evaluation of soil environmental health quality
Soil environmental health indicators mainly refer to elements or indicators that are directly or indirectly harmful to plant growth and human health. It can be divided into: ① pH; ② Environmental indicators: copper, zinc, cadmium, mercury, lead, arsenic, chromium and nickel; ③ Health indicators: F, I, Se; ④ Indicators of organic pollutants: organochlorine pesticides, etc.
According to the test index range of this study, the soil environmental health index will be selected from the first three items. Health indicators have double thresholds for crop growth, so the health indicators choose elements with abnormal (too high or too low) se, I and F contents in the soil; According to the results of environmental zoning of heavy metal indicators in the previous chapter, the soil in this area can basically be regarded as clean soil, and 90% of the soil in the study area belongs to the same type of soil, so Cu and Zn are combined as fertility indicators for discussion. See Table 4-42 for index screening results and index weight distribution.
Table 4-42 Weight Assignment Results of Soil Environmental Health Quality Indicators
(3) Establish the membership function model of evaluation index.
Membership function is a mathematical tool used to represent fuzzy sets, which mainly includes linear models and nonlinear models. According to the principle of practicality and simplicity of the evaluation work, this study adopts the peak model, the top model and the bottom model based on the linear model (Figure 4-43).
Figure 4-43 Various membership function models and membership value calculation formulas
In Figure 4-43, u is the upper limit of evaluation index; L is the lower limit of evaluation index; O 1 and O2 are the optimal values of the evaluation index, and X is the measured value of the evaluation index.
The principle of using membership function model for various geochemical evaluation indexes is as follows:
1) Soil pH, texture and soil health index are modeled by peak membership function.
2) beneficial elements of soil N, P, K, B, Mo, Mn, etc. adopts the upper-ring membership function model to evaluate the areas with high N and P content and serious water eutrophication, and the soil P and N can adopt the peak membership function model.
3) The membership function model is adopted for harmful elements such as arsenic, cadmium, mercury and lead in soil.
All geochemical indicators are counted by SPSS software. For data that do not obey normal distribution or lognormal distribution, the abnormal data are eliminated by the third average deviation until they obey normal distribution or lognormal distribution. For the data with normal or lognormal distribution, the evaluation index is scored according to the cumulative percentage values of 20%(L), 40%(O 1), 60%(O2) and 80%(U). See Table 4-43 for the limit value of each membership function and the corresponding relationship between the limit value of membership function and the scoring standard.
Table 4-43 Corresponding Table of Limit Values of Grading and Membership Functions
(4) Comprehensive evaluation
According to the technical requirements of geochemical evaluation of land quality, the comprehensive zoning of land environmental quality is divided into "equal" and "equal". Grading is the result of comprehensive division of soil environmental health quality and fertility quality. Using the hierarchical superposition scheme shown in Table 4-44, the land environmental quality of the evaluation plot is graded. * * * is divided into five grades: excellent, excellent, good, medium and poor, which are represented by color blocks. High quality is dark green, excellent is green, good is yellow, medium is pink, and poor is red. Based on the classification of land environmental quality, the comprehensive classification system of land environmental quality, that is, the comprehensive evaluation results of land environmental quality, is established by superimposing the quality of water environment (irrigation water) and the ecological effect index of plants (wheat is the key sampling plant in this area).
Table 4-44 Agricultural Geological Environment Quality Classification and Superimposing Scheme Table
The comprehensive grade of agricultural geological environment quality of each evaluation unit is represented by 3 digits. The agricultural geological environment quality is classified as excellent, good, medium, poor and poor 5. , respectively, represented by the numbers 1, 2, 3, 4 and 5, and placed in the first place of the evaluation index code. The quality evaluation index of irrigation water (shallow groundwater) is placed in the second place of the evaluation index code. If it does not exceed the standard, it is indicated by the number 1, and if it exceeds the standard, it is indicated by the number 2. The evaluation index of plant (wheat) ecological effect ranks third, with the number "1" indicating "not exceeding the standard" and the number "2" indicating "exceeding the standard". In this way, the quality of agricultural geological environment in this area can be divided into 5 grades and 20 grades (Table 4-45). Using this method to classify the quality of agricultural geological environment can directly reflect the internal and external environmental quality and ecological effect of land. After the database and information system are established, the evaluation results can be easily queried, which is very practical for land planning and utilization and land ecological management and protection.
Table 4-45 Comprehensive Classification Scheme and Code of Agricultural Geological Environment Quality (Grade 5 and Grade 20)
sequential
Third, the evaluation results
Soil fertility zoning
According to the evaluation results of soil essential macro elements, essential trace elements, beneficial elements and heavy metal elements, the regional map of agricultural soil geochemical environmental quality (Figure 4-44) is compiled:
Figure 4-44 Agricultural Soil Geochemical Environmental Quality Zoning Map
1. beneficial elements is rich in nutrition.
The total area is 8572.50km2, accounting for 15.78% of the study area. It is distributed in Yishu fault zone and its vicinity, western Gaomi, northern Weifang and parts of Qingdao and Yantai, mainly for river alluvial deposition and lake deposition. The area is relatively flat, with fertile land and abundant rainfall. Mainly planting wheat and corn crops, peanuts and fruits, it is the main grain-producing area in eastern Shandong. The heavy metal content in this area is low, and beneficial elements is rich in nutrients such as potassium, sulfur, magnesium, manganese, sodium, iron, boron, calcium, chlorine, cobalt and copper. Its good production conditions and high output are suitable for modern agricultural production, and it is also a favorable area for vigorously developing agriculture, animal husbandry and fishery.
2. Nutrition suitable area in beneficial elements.
The total area is 3 1 123.98km2, accounting for 57.30% of the study area. It is distributed in most areas of Jiaolai Basin and parts of Yantai, Weihai and Rizhao, and is characterized by basins, hills and mountains. Mainly distributed in Quaternary strata, some Mesozoic strata, and a small number of Neoproterozoic and Mesozoic granites. It is a suitable area for soil nutrition such as boron, calcium, chlorine, potassium, magnesium, sodium, sulfur and silicon in beneficial elements, with low content of heavy metal elements, good production conditions and high yield, which is suitable for modern agricultural production. Wheat, corn and other staple crops are mainly planted in Jiaolai Basin or some hilly areas, while forests, apples, pears, hawthorn and peanuts are mainly planted in mountainous areas and hilly areas, which are suitable for forest, agriculture and animal husbandry.
3. Nutrient deficiency areas (fertile areas) in beneficial elements.
The total area is 9847.65km2, accounting for 18. 13% of the study area. It is distributed in the south of the study area, east of pingdu city, Rushan-Weihai and coastal areas, characterized by low hills or marine alluvial plains, and mainly exposed granite and marine quaternary strata. In exposed rock areas or coastal plain areas, vegetation is scarce, soil and water conservation is poor, and human pollution is less. beneficial elements lacks nutrients such as N, P, K, B, Mo, Ca, Mg and organic matter, and the land is barren. Generally, it is necessary to fertilize the soil and apply trace element fertilizers appropriately, which can develop some cash crops and famous and special agricultural products.
4. Nutritional beneficial elements is deficient, and some heavy metal elements are high.
The total area is 4449. 12km2, accounting for 8. 19%, including Yantai, Rizhao, northern Jiaozhou Bay, Wendeng-Chengshanjiao and Linqu-Yishui, which are mainly distributed in hilly areas and small areas in plain areas. These areas are mainly polluted by heavy metal elements (three types of soil). Except for the comprehensive pollution of heavy metals such as Cu, Cd and Ni, most other areas in Yantai are polluted by single element of Ni. In addition, some nutrients such as organic matter, nitrogen, phosphorus, molybdenum and boron are also lacking. It is necessary to strengthen the research on pollution control and crop suitability in this area. According to the stress tolerance of crops, targeted measures can be taken to develop agriculture in a limited way.
5. Some areas are polluted by heavy metals (more serious than the three types of soil)
The total area is 325.74km2, accounting for 0.60%. It is distributed in Rizhao, Linqu, Yishui, Yantai and the northern part of Rushan City, mainly showing "point source" pollution. The contents of heavy metal elements such as Ni, Cu, Cd and Hg in these areas are high, and the soil is polluted to a certain extent (worse than the three types of soil), which is the forbidden area for some crops. Fertilization can block or reduce the activation and transfer of heavy metal elements in soil to crops, such as applying lime to improve pH value; Or apply organic fertilizer to increase the content of organic matter in the soil, or improve the soil through agricultural engineering, such as changing soil, dumping soil, deep ploughing and other methods, in order to reduce the harmful effects of heavy metal elements entering the work object and passing through the food chain. At the same time, we can also screen out the varieties of planting products suitable for soil pollution and physical and chemical properties, adopt low-enrichment rotation mode, make rational use of land resources, and also plant flowers, trees and grass.
(B) the results of comprehensive evaluation of land environmental quality
The present situation of land geochemical quality is shown in Table 4-46 and Figure 4-45. The land area of11and 12 1 which can be used as green food production bases is * * *1938.69 km2, accounting for 3.65%, and distributed in Juxian-Changyi and Laixi-0. The land area of Grade 1 12 caused by soil acidification and excessive irrigation water is 34.90km2, accounting for only 0.07%, which is distributed in Yantai City. Strengthening management and protection can also be used as a green food production base.
Table 4-46 Geochemical Evaluation Results of Land Quality in Eastern Shandong Province
Figure 4-45 Suggestions on Land Ecological Management and Protection
2 1 1 and 22 1 which can be used as pollution-free food production bases have the largest land distribution area, reaching 3 1 255.72km2, accounting for 58.95%, mainly distributed in Jiaolai basin and local urban areas. The land area of 2 12 and 222 is 1620.75km2, accounting for 3.06%, which is mainly distributed in Anqiu and the southwest of Yishui, followed by Rizhao and Yantai. Strengthening the management and protection of this land can also be used as a pollution-free food production base.
3 1 1 and 32 1 land, with a land area of 8084.38km2, accounting for 15.24%, distributed in the north of Changyi, southwest of Qinghai, Pingdu and Mu Ping-Rushan areas; The area of plots 3 12 and 322 is 162.85km2, accounting for 0.3 1%, which are distributed in the north of Changyi, the north of Rushan and some areas of Yantai, so the management and protection of these plots should be strengthened.
The land area of Grade 4 1 1 and Grade 42 1 is 5300.4 1km2, accounting for 10%, and none of the agricultural products planted at present exceed the standard. The land area of Grade 4 12 and Grade 422 is 3 136.82km2, accounting for 5.92%. 4. In some areas, soil acidity, soil heavy metals and irrigation water exceeded the standard, and heavy metals in some agricultural products exceeded the standard, mainly distributed in central Yantai, eastern Weihai, eastern Linqu, Linqu-Yishui, Rizhao and other places.
The land area of 5 1 1 and 52 1 is 12 17.50km2, accounting for 2.30%, and none of the agricultural products currently planted exceed the standard. The land area of 5 12 and 522 is 267.54km2, accounting for 0.50% of the study area. Grade 5 land is mostly located in various mining areas (gold mine, graphite mine, copper-iron mine), around villages and towns or adjacent to villages and towns. The soil is acidic and heavy metals exceed the standard, so it is very likely that the agricultural products planted will exceed the standard. Grade 5 soil in the north of Changyi City is strongly alkaline, with excessive irrigation water and extremely low nutrient content, which is not suitable for crop planting.