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A: Urea is synthesized with ammonia and carbon dioxide. During the granulation process, when the temperature exceeds 133 ° C, the urea will undergo a condensation reaction to produce biuret. Biuret has permeability, can cause dehydration of seed cells, and inhibit seed germination. If the biuret content of urea is high or the application method is improper, it will cause damage to seeds or seedlings. Urea is a high-concentration nitrogen fertilizer suitable for various soils and crops. To be reasonably and safely applied, the following points must be noted: First, qualified products should be selected. Note that the amount of fertilizer applied should not be too large, and the soil should be covered after application, especially for sandy land. It is necessary to apply a small amount of times, and do not immediately irrigate the water after application. Second, if you are making foliar fertilizer, you must use superior products, and prepare the concentration strictly according to requirements. Third, if the base fertilizer is to be applied 1 to 2 weeks earlier, and then planted; if it is to be sown and fertilized, it can be covered with a thin layer of soil after the application or ditch application, or misplaced fertilization, so that urea is separated from seeds and seedlings. open.
Mr. Xiao from Xianyang, Shaanxi Province asked: The urea solution should be sprayed in the later stage of wheat. It is said that the biuret content of urea should not exceed 0.5%. Where can I buy such fertilizer?
A: First of all, we must use the superior urea as the foliar fertilizer. The national standard (GB2440-2001) stipulates that the biuret content of industrial urea superior products shall not exceed 0.5%, and the biuret content of agricultural urea superior products shall not exceed 0.9%. If it is used for foliar fertilizer or large-area spraying, urea should be used for industrial superiority; for individual farmers, it is sufficient to use urea for agricultural superiority. Secondly, it is necessary to prepare and use foliar fertilizer strictly as required. Since various urea products contain biuret more or less, if the application is unreasonable (such as excessive concentration), even the superior urea may cause harm to the crop.
Mr. Liu from Luoyang, Henan Province: I used to buy a ternary compound fertilizer produced by a certain manufacturer. It is quite good. When I went to buy this year, I found that the bag contained “biuret, which would cause harm to cropsâ€. How is this going? Is the quality of fertilizers reduced?
A: The new "Compound Fertilizer" national standard (GB15063-2009) stipulates that the compound fertilizer containing urea nitrogen must indicate the above warning on the packaging container. Fertilizers that use urea as a nitrogen source for compound fertilizer generally contain a certain amount of biuret. Now the national standard requires fertilizer manufacturers to indicate warning signs on fertilizer containers, not only to regulate the fertilizer market, but also to be responsible for farmers. With warnings, the quality of fertilizer has not declined, but it has been more secure. For example, some farmers used to apply the nutrient content of 30-5-5 high-tower melt granulation compound fertilizer, because it is not known that the fertilizer contains a large amount of urea, so it contains more biuret, which is used as a base fertilizer in the early spring greenhouse. The application amount is large, it is not fully mixed with the soil, and the shed is not exposed in time, causing the transplanted seedlings to be damaged to varying degrees.
Ms. Tang from Qiqihar, Heilongjiang asked: In the fertilizer market, some compound fertilizer bags are marked with chlorine, but they are not written in Chinese, they are chemical symbols, and they are written very small. Is this correct?
A: No. National standards stipulate that when the compound fertilizer contains more than 3% chlorine, it must be marked with chlorine in the fertilizer container, and when it contains high chlorine (greater than 30%), it must also indicate the crop suitable for the fertilizer and improper use. Warning signs such as injuries caused by crops. As for the use of chemical symbols instead of the Chinese word "chlorine", it is not allowed to deceive the peasants, and the quality and authenticity of the products are also very doubtful.
Mr. Zhou from Tianshui, Gansu asked: I used a compound fertilizer produced by a company very effectively. I found that I changed the packaging when I bought it this year. The logo content is the same as in previous years, but the bag is painted with corn and rice patterns. Is this a fake? ?
A: This is the propaganda method of fertilizer manufacturers. If the logo content, manufacturer and purchase channel have not changed, just add a pattern and you can buy it with confidence. However, the national standard stipulates that for the compound fertilizer labeled “chlorineâ€, there should be no pictures of chlorine, crops, etc. on the packaging to prevent misleading farmers.
(Senior Consultant of Sinofert, Professor of China Agricultural University Wang Xingren)
Farmers Daily
Fertilizer commodity knowledge questions (1)
Ms. Su from Xiaogan, Hubei asked: Why does urea contain biuret, what harm does it have? How should urea be applied reasonably?
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