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There are two main ways to fertilize vegetables: one is to directly pollute vegetables or soil through harmful substances contained in fertilizers, such as heavy metals, pathogenic microorganisms, poisonous gases, etc. Second, the vegetables are produced by applying a large amount of nitrogen fertilizer. Excessive accumulation of nitrate. In order to reduce the pollution of vegetables by fertilization, the following points should be noted in fertilization:
Re-application of organic fertilizer and organic fertilizer will not lead to the accumulation of nitrate in vegetables, but also improve the quality of vegetables. The organic fertilizer is preferably applied after being fermented by high temperature stacking or biogas fermentation, which can kill germs and eggs, reduce the application amount of pesticides, and increase the yield and quality of vegetables. Vegetables grown with biogas fertilizer are the best pollution-free vegetables.
No or little application of nitrate-nitrogen fertilizer and nitrate-containing compound fertilizer can easily cause nitrate accumulation in vegetables, so it is not suitable for use on vegetables. Ammonium nitrogen fertilizer and ammonium amide fertilizer, such as ammonium sulfate and carbonic acid, can be used. Ammonium hydroxide, urea, etc.
The amount of nitrate in vegetables controlled by nitrogen application increased with the increase of nitrogen fertilizer application rate. The amount of nitrogen applied per mu should be controlled within 30 kg, of which 70% to 80% is applied as a base fertilizer and 20% to 30% is used as a deep application.
Nitrogen fertilizer should be applied early as a base fertilizer or as a base fertilizer in seedling stage, which is beneficial to the early growth of vegetables and is beneficial to reduce the accumulation of nitrate in soil and vegetables. The deep application of nitrogen fertilizer to the soil layer of 10-15 cm can reduce the loss of nitrogen and increase the utilization rate of nitrogen fertilizer. In deep soil, the soil air is in an anaerobic condition, and the nitrification is slow, which can reduce the accumulation of nitrate in vegetables.
Due to the high fertility of the soil due to the season, the soil rich in organic matter, vegetables tend to accumulate nitrate, should be applied or less nitrogen fertilizer. In low-fat vegetable fields, the nitrate accumulated in vegetables is lighter, and nitrogen fertilizer and organic fertilizer can be applied to fertilize the soil. In general, vegetable land, such as taking soil balance fertilization, is conducive to high quality and high yield, but also makes it difficult for vegetables to accumulate nitrate, and is also conducive to fertility. The high temperature in summer and autumn is not conducive to the accumulation of nitrate, and the amount of nitrogen fertilizer can be applied. In winter and spring, the temperature is low, the light is weak, the nitrate reductase activity is decreased, and nitrate is easily accumulated. Nitrogen fertilizer should not be applied or applied.
Because different types of vegetables are fertilized by vegetables, the degree of absorption and accumulation of nitrate is different. Cabbage and green leafy vegetables tend to accumulate nitrate, and nitrate fertilizer cannot be used. Solanum, fruit and root vegetables have higher nitrate accumulation. Less, can be applied properly, but the application of nitrate nitrogen fertilizer should be stopped 15 to 30 days before harvest.
Leafy vegetables should be sprayed with nitrogen fertilizer and nitrogen fertilizer for foliar fertilizer directly in contact with air. Ammonium ions are easily converted into nitrate ions and absorbed by leaves, and nitrate accumulation increases. Therefore, foliar application of nitrogen fertilizer should be prohibited in the production of pollution-free leafy vegetables, especially in the first month before harvest.
It is easy to be polluted by pouring sewage into sewage without using sewage. Any sewage discharged from factories and mines contains more toxic substances such as chlorine, arsenic, tin and lead, and should not be used for watering vegetables. Urban domestic sewage should be treated harmlessly, and after killing germs and eggs, it can be mixed with clear water.
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