Improper or excessive use of fertilizers not only reduces fertilizer utilization, wastes resources, reduces fertilization benefits, but also causes soil salinization. The most important thing is to reduce the quality of vegetables. In the pollution-free production, we must rationally apply fertilizer to minimize the impact of fertilization on the quality of vegetables.
1 The main problem of vegetable fertilization
1 . 1 Â Large amount of fertilization to form salt damage: According to the survey, the average ( mu ) of local greenhouse greenhouse vegetable production is about 4 cubic meters of high-concentration agricultural fertilizer such as chicken manure and pig manure , urea 35 kg, diammonium phosphate 100 kg, and potassium fertilizer 100 kg. It is also necessary to apply hundreds of kilograms of urea or ammonium nitrate . According to the test results of soil nutrients in vegetable fields and greenhouses in Datun Township in the past two years, the soil available nitrogen in greenhouse soil is 240 mg/kg or more, the available phosphorus is 150 mg/kg or more, and the available potassium is 450 mg /kg or more. The total amount is 5 . 29 g / kg. Relevant research has proved that one ounce of vegetables ( mu ) is 425 kg of ammonium nitrate , the soil water-soluble salt is up to 3 g/kg, and the total salt content of soil for growing greenhouse vegetables for many years is 20 g/kg. This has exceeded the salt content of salt soil, so the amount of fertilizer applied should be given enough attention.
1 . 2 The method of topdressing and fertilization is unreasonable: the application of base fertilizer in solar greenhouse adopts deep application and layered application technology, which is still a relatively scientific method. This will not only meet the needs of different plant nutrients period, and also prevents the loss of nutrients. However, the method of topdressing is extremely unreasonable. The main performance is that the fertilizer is placed in the water inlet, and the water is washed away when the water is discharged. This causes uneven fertilization, and the nutrients are lost, transformed, and volatilized with water, causing losses. At the same time, the topdressing variety is single, and only ammonium nitrate or urea is traced throughout the growth period, resulting in high levels of nitrate and nitrite in the seven soils and vegetables, which affects the quality of the vegetables.
1 . 3 insufficient attention to other elements and micro-fertilizers: the growth of vegetables requires not only a large amount of nutrients such as nitrogen, phosphorus and potassium, but also essential elements such as calcium, magnesium and sulfur. As long as one of the nutrients is lacking during the growth of vegetables, it will have an impact on the yield and quality of vegetables. However, many vegetable farmers pay insufficient attention to medium and trace elements, and the application of less or no application makes the greenhouse vegetables often prone to certain elemental deficiency, thus affecting the yield and quality of vegetables.
2 Main techniques for fertilization of pollution-free vegetables
2 . 1 Use a reasonable fertilization method: first select the fertilizer variety that has no or little effect on the quality of the vegetables after application. For example, potassium fertilizer should be applied with potassium sulfate fertilizer, and potassium chloride fertilizer should not be applied; ammonium nitrogen or amido fertilizer should be selected for nitrogen fertilizer application, and nitrate fertilizer should be used less or not. This can not only achieve high yield, but also reduce the nitrate and nitrite content in vegetable products, improve the quality of vegetables, and reduce the soil pollution caused by nitrate. In addition and in order to reduce the influence of excess nitrate soil and vegetables control recommendations to reduce the Nitrate and nitrite nitrogen having inhibitory properties of lime nitrogen, and carbon disulfide in vegetable production. Second, we must use a reasonable fertilization method. For the base fertilizer, deep application and shallow application should be combined to meet the needs of fertilizers in different growth stages of vegetables. Purse taken and centralized administration combined to meet the needs of the fertilizer and seedling improve the utilization rate. Summer and fertilizer for fertilizing preferably used, and for alternately applying fertilizers and urinary human excrement, be applied after watering way to improve the utilization of fertilizer and reduced nitrate, nitrite accumulation in the soil. For the greenhouse vegetables in the greenhouse due to the use of submerged dark irrigation in the winter can not be ditch or hole application, the fertilizer can be dissolved in a container, and then a thin tube is taken out into the water to make the fertilizer evenly applied to the person.
　　 2 . 2 Application of decomposed organic fertilizer: organic fertilizer not only contains various nutrients needed for vegetable growth, but also improves soil; adding organic fertilizer can not only meet the needs of vegetables for various nutrients, but also reduce vegetable pollution and improve vegetable quality. . When applying organic fertilizer, attention should be paid to full decomposing to prevent the contamination of vegetables by harmful microorganisms. Commonly used organic fertilizers are manure and manure, green manure, and soil fertilizer.
   2 . 3 Moderate reduction of chemical fertilizer use: Chemical fertilizers are appropriate and less applied, especially chemical fertilizers containing nitrogen, which is the main factor causing the accumulation of nitrate in vegetable plants. Therefore, in the production of pollution-free vegetables, the application amount of chemical fertilizers, especially nitrogen fertilizers , should be minimized , and the use of nitrate nitrogen fertilizers is prohibited. The total application rate of nitrogen fertilizer is generally controlled within 30 kilograms per ( mu ) , and it should be applied early and deep, pay attention to the combination of base fertilizer and top dressing, nitrogen fertilizer combined with phosphorus and potassium fertilizer application , and cover soil after application.
   2 . 4 Application of biological fertilizer: Biological fertilizer is different from organic and inorganic fertilizers. It does not provide the nutrients needed by plants, but can improve the nutrient conditions of the soil through the products of microbial activities, so that the soil can exert potential fertility or stimulate plant growth and development. Improve the disease resistance of plants and thus increase yield. Biological fertilizers should be applied in conjunction with other fertilizers to give full play to the effects of biological fertilizers. Azotobacter biological fertilizer comprising fertilizer, fertilizer decomposing bacteria, antibiotic fertilizer, compound fertilizer and the like.
   2 . The 5 types of vegetables and planting season application: easy to accumulate nitrate in vegetables such as spinach, cabbage, spinach, lettuce, should minimize nitrogen fertilizers on nitrate accumulation lighter vegetables such as tomato, eggplant, pepper, radish, carrot Such as fruit and vegetable root vegetables, cabbage, lettuce, etc., can be suitably applied. Klein summer growing season in a high temperature, the faster the growth rate of plants, metabolism, less accumulation of nitrate nitrogen fertilizer may be appropriate, a low temperature growing season of winter Haruna, weak light, the plant of nitrate reductase activity decreased easily To accumulate nitrate, less or no nitrogen fertilizer should be applied. Further, leafy vegetables can foliar fertilizer, nitrogen fertilizer can not do foliar spray.
   2 . 6 Control sewage irrigation: The sewage contains a large number of germs, eggs, heavy metal ions and toxic substances. Direct irrigation will pollute the vegetables, which must be used after harmless treatment, combined with irrigation with clear water, when the temperature is low in the morning and evening. get on.
   2 . 7 Targeted application of fertilizers for micro-fertilizers and other elements: Due to the long growth period of greenhouse vegetables, it is easy to cause lack of various nutrients. Therefore, in addition to the application of zinc, iron, boron and other micro-fertilizers in the base fertilizer, Spraying compound fertilizer and other elements from time to time during the growth period will not only increase the yield, but also improve the quality of the vegetables.  Â
   2 . 8 Promotion and application of vegetable special fertilizer: Vegetable special fertilizer is a kind of high-efficiency compound special fertilizer prepared according to the fertilizer requirement of each variety of vegetables. It has the advantages of nutrient, fast fertilizer, easy absorption, convenient application, etc. It can change the blind fertilization of vegetable farmers , excessive application of a certain nutrient without the disadvantage of applying other nutrients, and can reduce the production cost and increase the yield and quality of vegetables. . Improve the economic efficiency of solar greenhouses.
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