Because of the large amount of fertilizer in greenhouses, the winter and spring seasons are closed tightly, and the temperature is low and the light is weak. The activity of nitrate reductase in vegetables is low and nitrates are easily accumulated. How to reduce the accumulation of nitrate in vegetables by topdressing is a problem that should be paid attention to when fertilizing vegetables without pollution: 1. It is forbidden to use nitrate nitrogen fertilizer. Ammonium nitrate, potassium ammonium sulfate, phosphorus nitrate, potassium nitrate, and compound fertilizers containing nitrate nitrogen can easily accumulate nitrate in vegetables after application. Because 80% of the body's ingested nitrate comes from vegetables, nitrates are converted to nitrite under reducing conditions. Nitrite and human amines in the intestine and stomach synthesize carcinogenic substances—nitrosamines, which cause gastric cancer and esophagus. Cancers and other cancers and diabetes, blood poisoning, and brain, heart and other organs are deprived of oxygen, causing difficulty in breathing, nausea or even death. In addition, it is not suitable to apply chlorinated fertilizers such as potassium chloride and ammonium chloride. Chloride ions can reduce the starch and sugar content of vegetables, degrade quality and reduce yield, and residues in the soil can cause soil decalcification and cause compaction. Such as magnesium sulfate, ammonium sulfate and other fertilizers, applied to the soil, the decomposition of sulfate ions, not easily absorbed by vegetables and stay in the soil, endangering the growth of vegetables. Ammonium bicarbonate is prohibited from being used because of the high volatility of ammonia, which can easily cause ammonia damage. 2, control the amount of nitrogen fertilizer. Nitrogen fertilizer is an indispensable fertilizer for vegetable production, but it cannot be used excessively. To make vegetables meet national and international pollution-free standards, the nitrate content in vegetables must be reduced. To reduce the amount of nitrogen fertilizer, it should be based on the amount of fertilizer required by different vegetables, usually 10-12 kilograms of pure nitrogen per acre is appropriate, nitrogen fertilizer should be deep, and with the phosphorus and potassium fertilizer application or application of ternary Compound Fertilizer. After covering the soil in time, it is best to use chemical fertilizer infiltration or combined with drip irrigation under the membrane to apply to the roots, reduce the loss, increase the utilization rate, and stop top dressing before the harvest. 3, the application of ecological Organic Fertilizer. Eco-organic fertilizer produced by fermentation using livestock manure. If targeted with different elements, it will form a series of special fertilizer. The organic matter content of ecological organic fertilizer can reach 45%, and it can play a role in nitrogen fixation, phosphorus release, and potassium release for vegetables, and can also decompose residues of pesticides and chemical fertilizers. One ton of ecological organic fertilizer is produced, such as 2 to 2.5 cubic meters of fresh chicken, 0.2 to 0.3 tons of straw powder, 5 kg of corn flour, and 8 kg of multi-dimensional complexes. The first step is to mix the chicken dung and the straw powder and mix it with water, squeeze it into groups and squeeze water into your fingers, but do not drip, loosen your hands and loosen it. The water content is 45%, then add corn flour and multi-dimensional complex bacteria, Mix and blend again, leaving no blocks. They were piled up and covered with insulation film. In the spring, summer and autumn, it can be matured in 5-6 days, and it takes 7-10 days in winter to mature. Generally within 1-3 days, when the temperature in the heap rises to 80°C to kill E. coli and eggs, the odor of chicken droppings can be eliminated. Afterwards, the compost became loose and dried. After the compost has matured, lightly dry it for easy work. In addition, the use of bio-organic compound fertilizers, humic acid fertilizers, soil improvement, increase fertility, create a good environment for the growth of pollution-free vegetables. 4, the implementation of formula fertilization According to the characteristics of different vegetables need fertilizer and soil fertilizer conditions, determine the appropriate amount of nitrogen, phosphorus, potassium and Trace Elements and the corresponding fertilization techniques. According to the research results of the relevant departments, the maximum demand period of nitrogen, phosphorus and potassium in greenhouse vegetables is: cucumbers are grown in 30-52 days in 75-140 days after planting and sweet peppers are in 30-60 days. The optimal fertilizer (nitrogen, phosphorus, potassium) application ratio was 1:0.67:1.83 for cucumber, 1:0.38:1.75 for tomato, and 1:0.38:1 for sweet pepper. Although micronutrients are rarely needed for vegetables, they are indispensable. When using micro-fertilizers for surface spraying, good dosage standards, such as ferrous sulfate 0.1%-0.3%, zinc sulfate 0.05%-0.2% borax 0.3, should be used. %-0.5%, ammonium molybdate is 0.02%-0.05%, and copper sulfate is 0.02%-0.04%, which can be combined with disease prevention and spraying of Bordeaux multi-solution to treat both diseases and increase fertility. Or spray plus urea 0.1% -0.4%, potassium dihydrogen phosphate 0.2% -0.3%. Note that foliar vegetables should not be sprayed on the leaves to avoid increasing the nitrate content. Do not apply more diammonium phosphate, vegetables in general need a lot of nitrogen and potassium, less phosphorus, before and after flowering need potassium most, then gradually reduce. 5, limit the use of hormones. Some vegetable farmers do not talk about the quality of vegetables. In order to pursue high-yield, early-maturing, and early-morning markets, gibberellin (920), ethephon, paclobutrazol, and other hormones are used to promote long-lasting ripening, which greatly reduces the quality of vegetables. People will eat for a long time. Extremely unfavorable. China Agricultural Network Editor
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