The environmental quality evaluation of reclaimed soil is a quantitative description of reclaimed soil quality, which should be based on its suitability for human production, life and development and crops. Reclaimed farmland filled with coal gangue and fly ash may gain social and ecological benefits, but it may lead to unusable reclaimed soil due to environmental problems, such as the heavy metal content in reclaimed soil may exceed the standard and the pH value may be too high or too low. Farmland soil is a complex system, and the main factors affecting the environmental quality of reclaimed soil are soil acidity and toxic pollution. The former is evaluated by soil pH value, while the latter includes the evaluation factors of fluorine and heavy metal elements such as cadmium, mercury, arsenic and lead [149, 150] (see Table 6-5). The soil quality of reclaimed farmland is usually the result of a variety of soil environmental factors. Therefore, it is obviously inappropriate to use single factor pollutants to evaluate whether the soil is polluted, and it should be changed to multi-factor comprehensive evaluation [15 1]. According to the comprehensive methods of evaluating soil pollution at present, Nemerow's water index method is selected to calculate the comprehensive index of soil environment and evaluate the degree of soil health. The calculation formula is as follows:
Table 6-5 Evaluation Index of Soil Environmental Quality (mg/kg)
Study on landscape evolution and regulation of reclaimed farmland in coal mining area
Where: p is the comprehensive pollution index of soil; Pi is the pollution index of a pollutant, while Pi=Ci/Si, Ci is the measured value of a pollutant, Si is the evaluation standard of a pollutant, and it is the index average of various pollutants in the soil, and max(Pi) is the maximum pollution index of a single pollutant in the soil. According to the outline of environmental quality assessment of green food producing areas of China Green Food Development Center, the pollution grade standard is: P < 0.7 Very healthy; 0.7 ≤ P < 1 healthy; 1 ≤ P < 2 is healthy; 2 ≤ P < 3 is generally morbid; P≥3 disease.
The soil adopts the secondary standard in GB15618-1994 Soil Environmental Quality Standard (Table 6-6); The limit value of "Hygienic Standard for Food Inspection" shall be adopted for grain (Table 6-7); Vegetables are subject to Food Hygiene Limit Standard (Table 6-8).
Table 6-6 Secondary Standard Value of Soil Environmental Quality (mg/kg)
Table 6-7 Limits of Hygienic Standards for Food Testing (mg/kg)
Table 6-8 Limits of Hygienic Standard for Vegetable Detection (mg/kg)