To reduce the nitrate content of vegetables, the first is to apply reasonable fertilization, control the type and quantity of fertilization, and master the methods of fertilization. The second is to regulate the water, temperature, light and Other environmental conditions, so as to achieve the purpose of controlling the absorption rate of the root system of plants, reduce the absorption, and then accelerate the metabolism of nitrate in the plant, the key technologies are briefly summarized as follows:
First, a reasonable fertilization
1, select the appropriate nitrogen fertilizer varieties. The nitrate nitrogen absorbed by the vegetable plant from the soil is reduced to ammonia and then participates in the synthesis of amino acids to form proteins. If nitrate nitrogen does not have time to convert, it will cause the accumulation of nitrate. It can be seen that nitrate nitrogen fertilizer has a greater impact on the content of vegetables. Ammonium nitrogen fertilizer can also be converted to nitrate nitrogen by nitrification in dry land, with good ventilation and other suitable conditions. In addition, the improper use of urea and organic matter also tends to cause nitrate accumulation. Different kinds and forms of nitrogenous fertilizers have a great influence on the nitrate content of vegetables (ammonium nitrate> urea> ammonium bicarbonate> ammonium sulfate> ammonium chloride). When applying nitrogenous fertilizers generally, it is necessary to use urea, ammonium chloride, or nitrate nitrogen fertilizer (ammonium nitrate) ammonium nitrogen (ammonium chloride) in combination (a ratio of about 3:7), which can reduce the nitrate concentration, but also To make vegetables grow well, nitrate nitrogen fertilizer should be applied as little as possible.
2, appropriate control of nitrogen fertilizer. The application of nitrogen fertilizer was significantly correlated with nitrate accumulation in vegetables. Therefore, to ensure the quality of vegetables, it is necessary to properly control the amount of nitrogen fertilizers in vegetable fields. More organic fertilizer, humic acid fertilizer, and microbial fertilizer should be applied in the soil, and nitrogen fertilizer should be less applied. Reasonable organic and inorganic ratios can promote a lasting balance of nutrient supply, improve the nutritional environment of vegetables, and reduce nitrate accumulation. For example, the nitrate content of edible parts such as Chinese cabbage and spinach after application of organic fertilizer is reduced from 1000 mg/kg to about 600 mg/kg of single fertilizer. However, organic fertilizers should be applied after high-temperature heaping and decomposing to kill pathogens and eggs. The ability of different types of vegetables to absorb and accumulate nitrates is also different. Leaf vegetables> melons> eggplants are common.
3, nitrogen fertilizer should be used in conjunction with phosphorus and potassium. Phosphorus and potassium can promote the synthesis of proteins and important nitrogen compounds and reduce the accumulation of nitrate. When sufficient phosphorus is available, it can promote nitrate reduction and assimilation, and also increase the absorption of nitrate nitrogen by vegetables. Potassium is beneficial to the reduction and utilization of nitrate nitrogen, which can make the nitrate content in vegetables reach the minimum. Therefore, the balanced application of nitrogen, phosphorus and potassium has an important position in controlling the nitrate content of vegetables. The suitable ratio of nitrogen, phosphorus and potassium can not only increase the yield of vegetables, but also make the content of nitrate in vegetables reach the minimum.
4, strictly control the application of nitrogen fertilizers. Nitrogen fertilizer should be applied deeply and early. Deep application can reduce nitrogen volatilization, extend fertilizer supply time, and increase nitrogen fertilizer utilization. Early application promotes early and long-term growth of vegetable plants, prolongs fertilizer efficiency, and reduces nitrate accumulation. Fertilization should also be applied according to the type of vegetables, cultivation conditions, and climatic conditions.
In the production of pollution-free vegetables, the nitrate content is constantly changing. According to the study, as the time of topdressing with nitrogen fertilizers, nitrate content in vegetables has gradually decreased. For vegetables, the topdressing time should be arranged 30 days before harvest, and the principle of topdressing is “a small number of timesâ€.
5, increase nitrogen fertilizer synergist. Nitrogen fertilizer can inhibit the activity of nitrifying bacteria in soil and slow down the reaction rate of ammonium nitrogen in soil into nitrate nitrogen to reduce the accumulation of nitrate in vegetables. Commonly used are: N-pyrroline (CP) and dicyandiamide (DCD) consumption generally accounts for 0.5-3% of pure nitrogen in nitrogen fertilizers.
Second, a reasonable adjustment of water, temperature and light conditions
Nitrate content varies with the same vegetable under different environmental conditions. Generally, there is less accumulation of nitrate under adequate soil moisture, high temperature and strong light. On the contrary, there is a large accumulation of nitrate in the soil with low water content and low temperature and low light. Reasonable irrigation, reasonable dense planting, intercropping and other measures can improve the growing environment of vegetables and reduce their nitrate content. For greenhouses, greenhouses and other facilities, effective measures such as auxiliary light sources or timely updating of greenhouse films can be adopted.
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