Urea is a kind of high concentration nitrogen fertilizer, which belongs to neutral quick-acting fertilizer and can also be used to produce a variety of compound fertilizers. No harmful substances remain in the soil, and long-term application has no adverse effects. Animal husbandry can be used as feed for ruminants. However, when the granulation temperature is too high, a small amount of biuret, also known as biuret, will be produced, which will inhibit crops.
As a neutral fertilizer, urea is suitable for all kinds of soils and plants. Easy storage, convenient use and little damage to soil. It is a chemical nitrogen fertilizer with a large amount of use at present. Urea is synthesized from ammonia and carbon dioxide in industry under certain conditions.
Urea is easily soluble in water, and 105g is soluble in 100 ml water at 20℃, and the aqueous solution is neutral. There are two kinds of urea products. Crystalline urea is a white needle-like or prismatic crystal, which has strong hygroscopicity and caking after hygroscopicity, and its hygroscopic speed is 12 times faster than that of granular urea. Granular urea is translucent, with a particle size of 1 ~ 2 mm, smooth in appearance and obviously improved in hygroscopicity.
At 20℃, the critical moisture absorption point is 80% of the relative humidity, but at 30℃, it drops to 72.5%. Therefore, urea should be avoided to be stored in the open air in humid climate in midsummer. After adding hydrophobic substances such as paraffin wax in urea production, its hygroscopicity is greatly reduced.
Urea is suitable for base fertilizer and topdressing, and sometimes used as seed fertilizer. Urea is a molecule before transformation and cannot be absorbed by soil, so it should be prevented from losing with water. Ammonia formed after conversion is also volatile, so urea should also be covered with soil.
A small part of the soil transformation applied to the soil is dissolved in the soil solution in the form of molecules, adsorbed by the soil through hydrogen bonds, and most of the rest is hydrolyzed into ammonium carbonate under the action of urease, thus producing carbonic acid and ammonium hydroxide.