I. Preventive measures for soil pollution
1 Scientifically use sewage to irrigate farmland. There are many kinds of wastewater with complex components. Some industrial wastewater may be nontoxic, but when it is mixed with other wastewater, it becomes toxic wastewater. Therefore, when using sewage to irrigate farmland, it must meet different irrigation water quality standards; Otherwise, it must be treated before it can be used to irrigate farmland.
2. Rational use of pesticides and active development of high-efficiency and low-residue pesticides. Scientific use of pesticides can effectively eliminate crop diseases and insect pests and give full play to the positive role of pesticides. The rational use of pesticides includes: storage, transportation and use in strict accordance with the Regulations on Pesticide Management. Workers who use pesticides must know the relevant knowledge of pesticides, so as to reasonably choose the application scope, spraying times, application time and dosage of different pesticides and minimize the pollution of pesticides to the soil. It is forbidden to use pesticides with long residual time, such as HCH, DDT and other organochlorine pesticides. Developing high-efficiency and low-residue pesticides, such as pyrethroid pesticides, will help reduce the pollution of pesticides to the soil.
3. Actively promote biological pest control. In order to effectively control agricultural pests and reduce the pollution caused by chemical pesticides, it is necessary to actively promote biological control methods and use beneficial birds, beneficial insects and some pathogenic microorganisms to control agricultural and forestry pests and diseases. For example, protecting all kinds of beneficial birds that feed on insects; Use Trichogramma, ladybug, spider and other beneficial insects to control various pests and diseases of grain, cotton, vegetables, oil crops and forestry; Use microorganisms such as Bacillus and Cordyceps to control corn borer and Dendrolimus punctatus. Using biological methods to control agricultural and forestry pests and diseases has the characteristics of economy, safety, effectiveness and no pollution.
4. Raise public awareness of soil protection. The consciousness of soil protection refers to the thoughts, viewpoints, knowledge and psychology of specific subjects about soil protection, including their views on the nature, function and value of soil, their evaluation and understanding of soil, their understanding and measurement of soil utilization, their understanding of their rights and obligations in soil protection, and their ideas. In the development and utilization of soil, it is necessary to further strengthen the propaganda work of public opinion and let the broad masses of cadres and people know that the soil problem is a major event related to the prosperity of the country and the safety of the people. Let farmers and grassroots cadres fully understand the current severe soil situation and arouse their sense of urgency, urgency and historical mission.
Second, the control measures of soil pollution
1 bioremediation of contaminated soil. Soil pollutants can be purified by biodegradation or plant absorption. Earthworm is an animal that can improve the self-purification ability of soil, and can also treat urban garbage and industrial garbage, as well as harmful substances such as pesticides and heavy metals. Therefore, earthworms are known as "Hercules of Ecology" and "Purifier". Actively promote the use of microbial degradation agents contaminated by pesticides to reduce pesticide residues. Plant absorption to remove pollution: some non-edible plants such as flowers, trees and fiber crops can be replanted in heavily polluted soil, and some non-edible plants with strong heavy metal absorption ability can also be planted. For example, Adiantum Adiantum has a strong ability to absorb and aggregate heavy metals in soil, and its cadmium absorption rate can reach 10%. Continuous planting for many years can effectively reduce the cadmium content in soil.
2. Chemical methods of contaminated soil treatment. For the soil slightly polluted by heavy metals, the use of chemical amendments can transform heavy metals into insoluble substances and reduce the absorption of heavy metals by plants. The application of lime in acidic soil can increase the pH value of the soil and make cadmium, zinc, copper and mercury form hydroxide precipitation, thus reducing their concentrations in the soil and reducing the harm to plants. For the soil with excessive nitrate accumulation and flowing into groundwater, the application amount of nitrogen fertilizer should be greatly reduced, and chemical inhibitors such as urease inhibitor and nitrification inhibitor should be used to control the accumulation of nitrate and nitrite.
3. Increase the application amount of organic fertilizer. Adding organic fertilizer can increase the content of organic matter and nutrients in soil, which can not only improve the physical and chemical properties of soil, especially the colloidal properties of soil, but also increase the capacity of soil and improve its purification ability. In the soil polluted by heavy metals and pesticides, the application of organic fertilizer can increase the adsorption capacity of soil colloid, and at the same time, soil humus can complex pollutants, significantly improve the ability of soil to passivate pollutants, thus weakening its toxicity to plants.
4. Adjust soil redox conditions. Adjusting the redox state of soil greatly affects the behavior of heavy metal valence-changing elements in soil, which can transform some heavy metal pollutants into insoluble sediments and control their migration and transformation, thus reducing the harm degree of pollutants. Adjusting the soil redox potential, that is, the Eh value, is mainly achieved by adjusting the soil water-gas ratio. In production practice, it is often achieved through soil moisture management and farming measures, such as flood irrigation in paddy fields. When the Eh value can be reduced to 160mv, many heavy metals can generate insoluble sulfides, reducing their toxicity.
5. Change the rotation system. Changing the farming system will cause changes in soil conditions and eliminate the toxicity of some pollutants. According to research, the implementation of paddy-upland rotation is an effective measure to reduce and eliminate pesticide pollution. For example, the degradation rate of DDT and bhc pesticides in cotton fields is very slow, and the residue is very large, but the degradation of DDT and bhc can be greatly accelerated after changing water in cotton fields.
6 change the soil and turn over the soil. For lightly polluted soil, the method of digging deep or replacing pollution-free foreign soil is adopted. For heavily polluted soil, the method of removing topsoil or replacing foreign soil can be adopted. These methods have the advantages of thorough improvement and are suitable for small-scale improvement. However, the improvement of large-scale polluted soil is very troublesome and difficult to implement.
7. Implement targeted measures. For the treatment of heavy metal contaminated soil, the pollution can be reduced or eliminated mainly by bioremediation, using lime, adding organic fertilizer, adjusting soil Eh by irrigation, and changing soil. For the prevention and control of organic pollutants, measures such as increasing the application of organic fertilizer, using microbial degradation agents and adjusting soil pH and Eh can accelerate the degradation of pollutants, thus eliminating pollution. In short, according to the environmental protection policy of "prevention first", the primary task of preventing and controlling soil pollution is to control and eliminate soil pollution sources and prevent new soil pollution; For contaminated soil, all effective measures should be taken to remove pollutants in the soil, improve the soil and prevent pollutants from migrating and transforming in the soil.