urea

Agricultural urea and vehicle urea

  Urea

Molecular formula: CO (NH2) 2, with nitrogen content of 46%, belongs to neutral chemical fertilizer and has certain hygroscopicity. Long-term application has no adverse effect on soil. It can be used as base fertilizer and topdressing, suitable for all kinds of soil and crops, and is the most common and main nitrogen fertilizer at present.

When the temperature of urea is below 20 ℃ and the relative humidity is below 70%, it will not only not absorb moisture, but also evaporate water and reduce its water content; When the temperature exceeds 20 ℃ and the relative humidity is higher than 80%, it starts to absorb moisture, and becomes paste when it is serious. When the air is dried again, it will re agglomerate, which is only inferior to ammonium nitrate. When the urea aqueous solution is at 80 ℃, hydrolysis and decomposition reactions will occur, forming ammonium carbamate, ammonia gas and carbon dioxide respectively. Under acid and alkaline conditions, urea will decompose faster when it is heated. Urea is easy to combine with straight chain carbohydrates to form crystalline additional compounds; It forms a variety of double salts with various inorganic compounds, such as Ca (NO3) 2 · 4CO (NH2) 2, NH4Cl · CO (NH2) 2, CaChemicalbookSO4 · 4CO (NH2) 2, MgSO4 · 4CO (NH2) 2 · 3H2O, Mg (NO3) · 4CO (NH2) 2 · 2H2O, etc; It is easy to form urea phosphate, dicalcium phosphate and water with monocalcium phosphate, namely Ca (H2PO4) 2 · H2O+CO (NH2) 2 → H3PO4 · CO (NH2) 2+CaHPO4+H2O; With nitric acid, it is easy to form urea nitrate, CO (NH2) 2+HNO3 → CO (NH2) 2 · HNO3, which combines and relaxes the two; It can combine with formaldehyde to form urea formaldehyde compounds (uric acid rubber shrinks), in which the higher proportion of formaldehyde is urea resin, and the lower proportion is slow-release (effective) urea.

Urea is an important nitrogen fertilizer with high quality and efficiency. At the end of World War I, Germany began to use urea as fertilizer. Practice has proved that urea has a high nitrogen content and no side components, which shows a good yield increase effect on all crops. Since the 1950s, it has become a key nitrogen fertilizer variety developed by various countries. In the 15 years from 1960 to 1975, the global urea output has increased by 10.5 times, and it has gradually replaced ammonium nitrate since the 1970s, becoming the most widely used nitrogen fertilizer variety in the world. After urea is applied to the soil, a small part of it is absorbed by plants in the form of amide, and most of it is ammoniated under the action of urease, converted into ammonia, and then absorbed by plants. The decomposition rate depends on the soil quality, temperature and water content, generally in 3 to 10 days. Therefore, the fertilizer efficiency of urea is longer than other nitrogen fertilizers, and the nitrogen loss is less. Urea is an ideal fertilizer for topdressing outside the root, because it does not contain harmful ingredients to crops, is neutral, does not burn the stems and leaves, has strong moisture absorption, and is easy to penetrate into the leaves with water and be quickly absorbed by crops. The concentration of topdressing outside the root is generally 0.5%~2% in Chemicalbook. In order to improve the effect of urea utilization, in addition to correctly mastering the properties and application conditions of urea, attention should be paid to rational application. Urea is a neutral fertilizer and contains no harmful components. Hydrolysate NH+4 and HCO-3 can be absorbed and utilized by crops. It is applied year after year, and generally has no adverse effect on soil properties. It is applicable to all kinds of crops and soils, and its fertilizer efficiency is similar to that of ammonium sulfate with equal nitrogen content; The effect is better than that of ammonium sulfate when it is used in the "aged" paddy field which lacks active iron and is prone to hydrogen sulfide poisoning. Too much urea or too high biuret content will easily cause ammonia and biuret toxicity to crops; The higher the urease activity of crops, the more sensitive to the toxicity of urea and biuret. Urea can be used as a supplementary feed for anti nestling animals. In industry, urea is the raw material for the synthesis of urea formaldehyde, melamine formaldehyde resin, etc. Medically, it is used to manufacture tetracycline, phenobarbital, caffeine and other drugs. The dye industry uses it to produce vat brown BR, phthalocyanine blue B, etc. Urea is packed with plastic film inside and woven bag outside. It shall be stored in a dry warehouse, and shall not be stored and transported together with acids