Urea is the first synthetic organism, widely found in nature, such as fresh manure containing urea 0.4%. Urea production accounts for about 40% of China's current total nitrogen fertilizer production, is second only to ammonium bicarbonate one of Urea the major nitrogen fertilizer varieties.
Urea molecular formula is CO (NH2) 2, because in human urine contains this material, so named urea. Urea nitrogen (N) 46%, is the highest nitrogen content of solid nitrogen fertilizer. Industrial use of liquid ammonia and carbon dioxide as raw materials, high temperature and pressure conditions in the direct synthesis of urea, the chemical reaction is as follows.
2NH3 + CO2 → NH2COONH4 → CO (NH2) 2 + N2O urea soluble in water, at 20 ℃ 100 ml of water can dissolve 105 grams, the aqueous solution was neutral reaction. There are two kinds of urea products. Crystalline urea is white needle-like or prism-like crystal, strong hygroscopicity. Granular urea for the particle size of 1 to 2 mm translucent particles, the appearance of smooth, significantly improved hygroscopicity, is conducive to preservation.
Urea can be applied to both basal and top dressing. Urea is a physiological neutral fertilizer, in the soil does not leave any harmful substances, long-term use without adverse effects. Urea is an organic nitrogen fertilizer, through the soil urease action, hydrolysis into ammonium carbonate or ammonium bicarbonate, can be absorbed by crops. Therefore, the urea should be applied 4 to 8 days before the crop needs.
Plant indispensable nitrogen fertilizer
Plant cell proliferation, organ construction, mainly rely on nitrogen nutrition. Nitrogen nutrition is an important component of chlorophyll, chlorophyll plays a major role in photosynthesis of fruit trees. Nitrogen nutrition is sufficient to help photosynthesis, increase tree nutrition, can make branches grow robust, leaf hypertrophy and thick; can improve the photosynthetic efficiency of leaves, increase the accumulation of organic nutrition, promote flower bud formation, flowering fruit set, the results increased quality excellent.
Urea Excessive and lack of urea are not appropriate
Excessive nitrogen in the plant body, it will cause the carbohydrate and nitrogen within the tree to lose balance or the relationship between the other elements of the imbalance, resulting in vegetative growth too long, branches and leaves long, flower bud differentiation, fruit drop fruit; delayed fruit ripening , The color of the fruit color, fruit flesh thick; sugar content and fruit hardness decreased, intolerant storage, physiological diseases, tree winter ability to reduce.
Urea chemical properties
Can be generated with acid salt. There is hydrolysis. In high temperature can be condensation reaction, generating biuret, biuret and cyanuric acid. Heated to 160 ° C decomposition, resulting in ammonia at the same time into isocyanic acid. Urea Because in human urine contains this substance, so
Named urea. Urea nitrogen (N) 46%, is the highest nitrogen content of solid nitrogen fertilizer.
Urea in the acid, alkali, the role of enzymes (acid, alkali to be heated) can produce ammonia and carbon dioxide hydrolysis.
Heat is unstable and heated to 150-160 ° C to deamination into biuret. Copper sulfate and biuret reaction was purple, can be used to identify urea.  if the rapid heating will be ammonia and trimer into a six-membered ring compound cyanuric acid. (Mechanism: first ammonia production of isocyanic acid (HN = C = O), and then poly-poly.)
With acetyl chloride or acetic anhydride can produce acetylurea and diacetyl urea.
In the role of sodium ethoxide and diethyl malonate reaction to produce malonyl urea (also known as barbituric acid, because it has a certain acid).
In the role of ammonia and other alkaline catalyst with formaldehyde reaction, polycondensation into urea-formaldehyde resin.
And hydrazine hydrate formation of semicarbazide.
Urea soluble in water, 100 ml of water at 20 ℃ can dissolve 105 grams, the aqueous solution was neutral reaction. There are two kinds of urea products. Crystalline urea is white needle or prism-like crystal, hygroscopicity, moisture after caking, moisture absorption rate 12 times faster than granular urea.  granular urea for the particle size of 1 to 2 mm translucent particles, the appearance of smooth, hygroscopic significantly improved. 20 ℃ when the critical moisture absorption point of 80% relative humidity, but 30 ℃, the critical moisture point dropped to 72.5%, so the urea to avoid the summer heat in the open storage. In the urea production by adding paraffin and other hydrophobic substances, the moisture absorption greatly decreased.