Because of the heavy metal and other pollution of the agricultural ecological environment of the vegetable base, the use of chemical fertilizers and pesticides in the vegetable production process has caused problems such as heavy metal, nitrate, and pesticide contamination in vegetable products. At this stage, it is still quite outstanding. After vegetables are harvested, secondary pollution is also present to a certain extent due to unreasonable preservation, storage, and processing. There are heavy metals, nitrates, pesticides and other harmful substances in vegetables. It will affect the health and safety of consumers. Therefore, how to prevent and control vegetable pollution is an urgent problem to be solved in real life. Now we introduce the prevention and control technologies as follows, to the readers.
1 origin selection
(1) The place of production of vegetables should be far away from factories, hospitals, mining areas, living areas, main arterial lines, and dump sites.
(2) The value of relevant pollutants in environmental factors such as air, water, soil, etc. in the area to be selected does not exceed the relevant national standards.
(3) According to the current industry's technical level of heavy metal pollution treatment in soil-vegetable system, to determine the appropriate relaxation of the limits of soil heavy metal content, for the lower pollution of soil, after improved governance, as long as the output of heavy metal content of vegetables does not exceed the standard Is considered for use.
2 Selection of vegetable varieties (variety) According to our research, the order of nitrate content in different types of vegetables from the smallest to the largest is Solanaceous Fruits 3 Optimized fertilizer structure and improved application method.
(1) Apply organic fertilizer. Organic fertilizers have a slower, longer-lasting and richer balance of nutrient release, which helps to reduce the accumulation of nitrates in vegetables. At the same time, organic fertilizers are used to increase soil environmental capacity and the adsorption capacity of soil colloids to heavy metals and pesticides is increased. Organic matter is also a reducing agent. Promote the formation of cadmium sulfide precipitates in the soil and promote the conversion of high chromium (cr6+) to lower toxicity chromium (cr3+). The proportion of organic fertilizer application depends on the species, soil, and time, such as green leafy vegetables with high nitrate accumulation. The application ratio of organic fertilizers should be appropriately increased; conversely, for beans, melons, and solanaceous fruit with lower nitrate accumulation, the ratio of organic fertilizers can be appropriately reduced. Soil heavy metal pollution is more important, and organic fertilizer ratio is higher; Is low. When using each organic fertilizer continuously, the ratio can be appropriately reduced: otherwise. Increase.
(2) Fertilizer varieties selection. According to our research, the nitrate accumulation of vegetables with different amounts of N fertilizers and other N fertilizers was in the order of NH4N03> NH4HC03> CO(NH2)2> (NU4)2S04> NH4CI. In order to reduce the accumulation of nitrate in vegetables, production should be considered to avoid the use of nitrate-containing fertilizers, ammonium bicarbonate, reasonable development and utilization of ammonium chloride and ammonium sulfate. It is also possible to use Cl-fertilizer in combination with other nitrogenous fertilizers, and to use Cl- to inhibit the activity of nitrosating bacteria and reduce the soil nitrification intensity. Reduce nitrate accumulation in vegetables. Slow and controlled release fertilizers are beneficial to increase fertilizer utilization and reduce the amount of nitrate accumulated in vegetables. In addition, fertilization also affects soil ecological environment and heavy metal activity. Studies have shown that different forms of nitrogen, phosphorus, and potassium fertilizers have different effects on soil physicochemical properties and the rhizosphere environment. Some forms of chemical fertilizers are more conducive to reducing soil heavy metal activity and heavy metal concentrations in plants. For example, comparing various phosphorus fertilizers that reduce cd capacity in crops, calcium, magnesium, phosphorus, calcium dihydrogen phosphate, phosphate rock, and calcium. The occurrence and development of vegetable pests and diseases are also closely related to chemical fertilizers. Therefore, production should be based on the principle of overall consideration to choose suitable fertilizer.
(3) Controlling N and balanced fertilization, nitrogen fertilizer should be applied early and deeply in concentrated planting: Studies have shown that there is a significant positive correlation between nitrate content in vegetables and N application level, so production should be based on the N characteristics of vegetables, and reasonable control of N levels. To avoid excessive application of nitrogen fertilizer. At the same time, we must also avoid partial nitrogen fertilizers, increase phosphate fertilizers, promote sugar conversion and respiration, promote N metabolism, and accelerate the synthesis of amino acids and proteins. The role of K in the body is multi-faceted, it can not only promote NO, absorption, but also reduce NO-3, and mainly reduce, promote amino acid protein synthesis. Application of potassium is one of the measures to reduce vegetable NO3, but this effect of K+ only plays a role in the growth process and NK balance. Increasing the application of trace elements such as Mo can increase the activity of nitrate reductase in vegetables, thus reducing the accumulation of nitrate in vegetables. Nitrogen fertilizer as a base fertilizer should be applied in deep layers. Early application of seedling fertilizer should be promoted as early as possible. Strictly controlling the interval between the last application of fertilizer and harvesting of vegetables has a suitable safety interval to ensure that the absorption of N03 in vegetables is sufficient for metabolism in the body. time.
(4) Add nitrification inhibitors for nitrogenous fertilizers, use soil heavy metal deactivators (disinfectants) and soil amendments: Add nitrification inhibitors to reduce soil digestion and reduce N0-3 accumulation in vegetables. Our studies on a variety of inhibitors show that the effect of dicyandiamide is better. Production of dicyandiamide generally accounts for 6% to 8% of purified N fertilizers. Lime application rate of 20-25 kg per 667 m2 can adjust soil pH, disinfect and sterilize, and reduce soil heavy metal activity. Sulfur application of 1.5-2kg per 667 m2 is also effective in reducing soil heavy metal activity.
(5) The quality of sludge, waste fertilizer, pulverized coal ash, and organic fertilizer shall be used up or harmlessly treated. At the same time, the amount of sludge, waste fertilizer, and pulverized coal slag shall be strictly controlled, and the relevant requirements shall not be exceeded.
4 Reasonable irrigation and drainage vegetables are closely related to the absorption, transportation and conversion of nitrate nitrogen. The nitrate reductase activity of vegetables is affected under drought conditions. The accumulation of nitrate nitrogen significantly increased. in many circumstances. Irrigation during the first few days of harvest can reduce the nitrate content of vegetables. By controlling the moisture, adjusting the soil redox status can affect the existence of heavy metals. Such as Cd, Pb heavily polluted soil to replant aquatic vegetables, is conducive to reduce the harm of Cd, Pb. The use of deep-gaug and narrow-gauge compartments ensures that the interior of the cabin, the gutters, and the waist are connected to each other to prevent waterlogging and reduce the risk of vegetable pests and diseases.
5 Enhance ventilation and light transmittance is sufficient to increase the activity of nitrate reductase in vegetables and reduce the accumulation of vegetable N03. At the same time, it is also conducive to the growth of vegetables and robust, improve the resistance to diseases and insect pests, so greenhouse vegetables should pay attention to promptly cover the ventilation and light, maintain the shed Internal air circulation.
6. Intercropping for interplanting between crops. Scientific arrangement of cornices. Use the reciprocal and antagonistic effects between species to reduce the risk of pests and diseases. Under the crop rotation system, the former soil flooded rice is conducive to the formation of insoluble sediments such as Cd, Pb, etc., to reduce its harm to the subsequent vegetables.
7 Strengthen pest forecast and forecast, accurately use pesticides to make field investigations of pests and diseases, master the occurrence and development of pests and diseases, and prescribe the right medicine. For pesticide selection, biopesticides and biochemicals are preferred; followed by low-toxicity and low-residue pesticides; once again encountering pests and diseases, the medium-toxicity and low-residue pesticides with good efficacy are selected. Strictly control the dosage of pesticides according to the use requirements and master the safety interval of pesticides.
8 Vegetables should be stored and processed immediately after harvest. The N0-3 in the body can be further transformed into NO, which will increase the harm to the human body. Therefore, the vegetables are not easy to store for a long time and should be treated in time. Our research shows that, after harvesting of contaminated vegetables, the residual NO3 and pesticides in the body are washed out by washing with water, but the content of NO3 remains unchanged. After salting and cooking, the content of N03 in vegetables decreased by nearly 50%, but the content of N03 in vegetables after salting had doubled, and only after cooking, the content of NO3 in vegetables decreased. The vegetables should be submerged and flooded to be eaten.
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