How to use urea reasonably? Why is it good to use urea as extra-root topdressing?

Urea contains 46% nitrogen, which is the highest in solid nitrogen fertilizer. It is also a physical neutral fertilizer, which is the most commonly used high-quality nitrogen fertilizer in production at present. So how to use urea rationally? Why is it good to use urea as extra-root topdressing?

The form of nitrogen in urea is different from that of ammonium bicarbonate and ammonium sulfate. after it is applied to the soil, some of it can be directly absorbed by crops, but most of it is hydrolyzed into ammonium bicarbonate or ammonium bicarbonate by urease. The hydrolysis rate is related to temperature. The soil temperature is high, the transformation is fast, the fertilizer effect is short; the soil temperature is low, the transformation is slow, but the fertilizer effect is long. In addition to nitrogen literacy, urea also contains carbon dioxide, which contributes to crop photosynthesis. In recent years, fluidized bed technology has been used to produce large granular urea with a diameter of 1.8 to 4.5 mm, or larger particles due to the need of agricultural production. It has good compression and moisture resistance, slow release and long fertilizer effect, so it is a good raw material for bulk mixed fertilizer (BB fertilizer).

It is best to apply urea as base fertilizer, such as in paddy field, it should be applied deeply before irrigation, because urea is not easy to be absorbed by soil and is easy to be lost with water. Urea should also be applied deeply as topdressing. The nitrogen content of urea is high, so the dosage should not be too much each time, and the high concentration will affect the growth of crops. Urea should not be directly used as seed fertilizer, because the high concentration of urea is in direct contact with the seed and can often penetrate into the protein of the seed cell, denaturing the protein and affecting the seed germination.

PS: why is it good to use urea as extra-root topdressing?

The effect of urea used for foliar spraying is better than that of other nitrogen fertilizers, because:

① urea is a neutral organic nitrogen with low ionization degree and small molecular volume, so it is easy to enter into leaves and is not easy to cause damage to crop stems and leaves.

② diffuses faster than ammonium ion and nitrate ion. After entering the body, it can quickly participate in the nitrogen metabolism of crops.

③ urea has a certain hygroscopicity. When the water of the spraying solution evaporates and the urea remains on the leaf surface, it can still absorb moisture and dissolve again, so the utilization rate is higher.

④ urea aqueous solution is neutral and stable, and can be sprayed mixed with many kinds of pesticides, which can not only provide nutrients, but also control diseases and pests and improve work efficiency. The concentration of urea as extra-root topdressing is 0.2%-1.0%. If the concentration is too high, it will damage the leaves and even cause the death of crops.

The suitable spraying concentration for various crops is 1% for rice and wheat, 0.5% for vegetables and fruit trees, 0.2% and 0.3% for cucumbers, tomatoes and eggplant in strawberries, flowers and protected vegetables. Usually spray once every 7 days, continuously spray 2 times 3 times, every 667 square meters each spray 50 kg 75 kg, with the leaf spray wet for degrees.