Urea, which is diamine carbonate, has a nitrogen content between 44% and 46%, and biuret should be between ≤ 0.9% and 1.5%. At present, China's solid ammonia fertilizer contains the highest amount of nitrogen in the fertilizer, pure white or slightly yellow crystals or small particles, add anti-wetting agent, moisture absorption is small, easily soluble in water, for the neutral nitrogen fertilizer. Urea has high nutrient content and is suitable for all kinds of soils and a variety of crops. It is most suitable for topdressing, especially for applying fertilizers outside the roots.
Urea is applied to soil and can only be absorbed and utilized by crops in large quantities only after it is converted into ammonium bicarbonate. Due to the process of transformation, the effect of fertilizer is slow, and it is generally 4 to 6 days ahead of schedule. At the same time, it is also required to apply deep cover soil, and do not apply water immediately after application to prevent nitrogen from leaching into deep layers and reduce fertilizer efficiency.
When topdressing with urea, especially foliar, the absorption of nutrients in urea is very fast, and the utilization rate is also high, and the yield increase effect is obvious. When spraying urea, the concentration requirements are more stringent. Generally, the concentration of the grass crop is 1.5% to 2%, the fruit tree is 0.5%, the exposed vegetable is 0.5% to 1.5%, and the greenhouse vegetable is between 0.2% and 0.3%. For highly productive crops or adult fruit trees, the concentration of urea applied can be appropriately increased.
Use urea should pay attention to the following questions:
(1) It is generally not directly used as seed fertilizer. Because urea contains a small amount of biuret, usually less than 2%, the biuret is harmful to the germination and growth of the seed. If it is necessary to make fertilizer, seeds and urea can be separated from the ground, and urea can not be used for seed soaking or seed dressing.
(2) When the biuret content is higher than 0.5%, it cannot be used as a top dressing.
(3) After urea is converted into ammonium bicarbonate, it is easily decomposed and volatilized on calcareous soil, causing loss of nitrogen. Therefore, it is necessary to deeply cover the soil.
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