① Nitrogen fertilizer. Nitrogen fertilizer applied to watermelon includes inorganic nitrogen fertilizer and organic nitrogen fertilizer. Proper amount of nitrogen fertilizer is an essential nutrient for the growth and development of watermelon. However, excessive nitrogen fertilizer not only changes the physical properties of soil and pollutes water sources, but also has a direct impact on nitrate accumulation in watermelon, and different nitrogen forms have different effects. For example, the nitrate content in watermelon fruit with nitrate nitrogen application is significantly higher than that with ammonium nitrogen application. Therefore, when a small amount of nitrogen fertilizer is needed, it is best to apply urea or ammonium sulfate.
② Phosphate fertilizer. The pollution of phosphate fertilizer to the environment mainly includes three aspects, namely, heavy metal, fluorine and radioactive pollution contained in phosphate fertilizer. First of all, phosphate fertilizer used all over China contains many kinds of heavy metals. According to the investigation, the average milligrams of various heavy metals in one kilogram of phosphate fertilizer are as follows: arsenic 34.2, cadmium 2.6, chromium 1 18, copper 57.8, nickel 12.8, lead 332.5, strontium 4 12.8 and titanium/kloc. Judging from the content, it is not harmful to the environment at present, but its potential harm can not be ignored. Secondly, no matter what type of phosphate fertilizer, the fluorine content is basically proportional to the phosphorus content, and long-term application will increase the fluorine content in the soil. In addition, natural radioactive elements such as uranium, radium and thorium are often associated with phosphate rock and enter phosphate fertilizer together in the process of phosphate fertilizer production. Chloral in phosphate fertilizer is also harmful. When using phosphate fertilizer containing chloral, it should be dried in advance to volatilize some of it, and it is better to sprinkle it when using it.
③ Silt. China rural areas are used to using river mud, pond mud, reservoir mud or ditch mud as fertilizer. Sludge contains a lot of organic matter (> 20%) and is rich in nitrogen, phosphorus, potassium and trace elements. It is a good soil improver and fertilizer, but it also contains a lot of heavy metal elements such as chromium, nickel, cadmium and lead. After these heavy metal elements are absorbed by crops, they will cause poor growth of crops and endanger the health of people and livestock.
④ Municipal garbage. There is a large amount of municipal solid waste, which is used as fertilizer in many areas. Garbage manure has a certain fertility, which has a good effect on improving soil total nitrogen and available nutrients. However, garbage manure contains some heavy metals, which will cause soil pollution when applied to Gua Tian. Therefore, the use of municipal solid waste fertilizer must be strictly controlled. It is best to apply it in heavy soil, which can not only increase nutrients and fertilize the soil, but also will not deteriorate the physical properties of the soil. China has also made corresponding regulations on the use of municipal waste fertilizer.
⑤ Organic fertilizer. Refers to human, livestock and poultry manure, which is the main fertilizer used in agricultural production. Organic fertilizer contains a lot of organic matter and various inorganic nutrients needed by crops. Generally, the utilization rate of nitrogen, phosphorus and potassium in decomposed human urine and chicken and duck manure is 20% ~ 40%, pig manure is 15% ~ 30%, and soil fertilizer is only 5% ~ 30%. Pollutants in organic manure, mainly manure itself or its decomposition products, such as a large number of pathogenic bacteria, malodorous components and products such as hydrogen sulfide, alcohols, phenols, aldehydes, ammonia and amines produced by decomposition under anaerobic conditions, will cause serious pollution to water, air and soil environment. So it must be composted to reduce pollution before it can be used. (2) The first principle of pollution-free watermelon fertilization is to balance fertilization according to the soil nutrient content and the law of watermelon fertilizer demand. 2. The types of fertilizers allowed to be used include: farmyard manure (cake manure, compost, biogas manure, green manure and crop straw), commercial organic manure (including humic acid manure and treated human and animal manure) registered or exempted from registration by the agricultural administrative department, microbial manure (including microbial agents and fertilizers treated by microorganisms) and chemical fertilizers (including nitrogen fertilizer, phosphorus fertilizer and chemical fertilizer). Third, it is forbidden to use fertilizer varieties that have not been registered by the administrative department of agriculture, urban garbage that has not been treated harmlessly, and garbage containing heavy metals. Avoid using chlorine-containing compound fertilizer. (3) Fertilization technology of pollution-free watermelon ① Organic fertilizer should be the main fertilizer, supplemented by inorganic fertilizer; Pay attention to reasonable base fertilizer and topdressing. Farmhouse manure used in pollution-free watermelon production should be fermented at high temperature, such as 50 ~ 70℃/kloc-0 ~15 days or more, to decompose organochlorine pesticides and kill pathogenic bacteria, eggs and weed seeds. Among them, high-temperature composting is better than composting, and the combination of organic fertilizer and inorganic fertilizer can obviously reduce nitrate content. Besides using organic fertilizer to improve soil fertility, topdressing is also needed. In order to avoid environmental pollution and nitrate accumulation in watermelon fruit, we should pay attention to the types, dosage and period of topdressing. The specific fertilization method is: medium fertility soil, the application amount and application method per 667m base fertilizer are: 4,000-5,000 kg of high-quality organic fertilizer (taking high-quality decomposed pig manure as an example), 6kg of nitrogen fertilizer), 3 kg of phosphorus fertilizer (P2O5), 7.3 kg of potassium fertilizer (K2O), or the compound fertilizer transformed from it. Half of the organic fertilizer is scattered, half is put in the melon ditch, and all the chemical fertilizer is put in the melon ditch. Fertilizer goes deep into the soil and mixes with it. The application amount and method of topdressing per 667㎡ are as follows: topdressing 5 kg of available nitrogen fertilizer (N) at the initial stage of grape jointing; When the eggs begin to fall off, 2.7 kg of phosphate fertilizer (P2O5), 5 kg of potash fertilizer (P2O5) or 75 kg of cake fertilizer should be applied topdressing every 667 meters. Fertilizer is mainly applied with water to avoid damaging the stems and leaves of watermelon. When topdressing, nitrogen fertilizer is only used in the early stage of watermelon growth to promote the rapid formation of watermelon nutrient areas; In order to avoid the bad effect of nitrogen fertilizer on watermelon quality, only phosphorus and potassium fertilizer should be applied when topdressing.
② Popularize formula fertilization technology. The central content of formula fertilization is "formula" and "fertilization". The formula is to estimate how much nitrogen, phosphorus and potassium crops need according to soil fertility, crop status and target yield, and then calculate soil supply parameters according to the measured values of soil nutrients. The difference between them lies in the application amount of nitrogen, phosphorus and potassium fertilizer. "Fertilization" is to reasonably arrange the proportion, frequency, cycle, dosage and method of base fertilizer and topdressing according to the fertilizer variety, dosage and soil and crop characteristics determined by the formula.