Urea is suitable for use as a base fertilizer and topdressing, and sometimes as a seed fertilizer. Urea is a molecular state before conversion and cannot be adsorbed by soil, so it should be prevented from losing with water. The ammonia formed after conversion is also volatile, so urea should also be deeply coated. (Soil transformation) A small part of the applied soil is dissolved in the soil solution in a molecular state and adsorbed by the soil through hydrogen bonding, while the rest is hydrolyzed to ammonium carbonate under the action of urease, which in turn produces carbonic acid and ammonium hydroxide. Then ammonium ion can be absorbed by plants and soil colloid adsorption, bicarbonate ion can also be absorbed by plants, so urea does not remain any harmful components after application into the soil. In addition, biuret contained in urea can also be decomposed into ammonia and carbonic acid under the action of urease. The conversion of urea in soil is affected by soil PH value, temperature and water, and the reaction is neutral in soil. The higher the soil temperature is when the water is appropriate, the faster the conversion will be. When the soil temperature is 10 ° C, it takes 7-10 days for urea to be completely converted into ammonium nitrogen, 4-5 days at 20 ° C, and 2-3 days at 30 ° C. Urea hydrolysis produces ammonium nitrogen, and surface application will cause ammonia volatilization, especially on alkaline or alkaline soil, so urea should be applied deep in the cover soil, and the paddy field should be applied deep to the reduction layer.)