First, the characteristics of urea
Urea is an amide nitrogen fertilizer, is currently the main varieties of nitrogen fertilizer, nitrogen fertilizer used in the varieties, urea accounted for more than half. Its main features are:
(1) the highest nitrogen content in solid nitrogen fertilizer. Generally nitrogen (N) 46%.
(2) water-soluble quick-acting nitrogen fertilizer. Urea in the soil before the application, its chemical stability, unlike ammonium bicarbonate as easy in the air decomposition, Urea is the majority of farmers favorite nitrogen fertilizer varieties. Urea to do topdressing, with less, quick.
(3) urea is a neutral, molecular state of organic nitrides, crop roots can directly absorb the molecular state of urea, but the number is very small. Urea into the soil, only in the soil under the action of urease, was hydrolyzed into ammonium nitrogen, the crop can be a large number of root absorption.
(4) urea need to be transformed into a large number of crops can be absorbed. Urea in the soil of the product is ammonium carbonate and ammonium bicarbonate, therefore, urea into the soil after the chemical properties of agriculture and ammonium bicarbonate similar, Urea it will also occur the loss of ammonia loss, so deep cover soil. The kind of urea that is not "gas fat" can be a misunderstanding.
Second, the application of technology
Urea can be used as basal and top dressing application, generally do not directly do fertilizer. Because the master is not good, high concentrations of urea will affect the seed germination and root growth. If you must do seed fertilizer application, to separate with the seeds, Urea and the amount of urea should not be more.
1, basal fertilizer
Urea as base fertilizer application, the application of the amount of careful planning, because urea nitrogen content is high, high concentration of nitrogen fertilizer, the amount must be appropriate, otherwise it will cause malnutrition, reduce nitrogen utilization. Urea With urea as a base fertilizer must be applied to a certain depth of the soil, especially in the slightly alkaline calcareous soil, if the table urea, ammonia volatilization loss than ammonium bicarbonate even more serious, up to 30% to 60 %.
2, top dressing
Crops in the sowing period or jointing application, can be used ditch facilities or facilities, after fertilization covered with cover to prevent ammonia after hydrolysis of volatile. Urea in the soil for topdressing, fertilization period than ammonium sulfate, ammonium bicarbonate and other quick nitrogen fertilizer varieties in advance a few days before the application, Urea because urea can only be converted into ammonium nitrogen can be a lot of crop absorption. How long is the day ahead, depends on the season and temperature, early spring weather (low temperature 10 ℃) to advance 6 to 7 days, late spring and early summer (16 ~ 20 ℃) 3 to 4 days ahead of the summer 1 to 2 days in advance. In the sand on the leaking leakage of water is more serious, each fertilizer should not be too much.
Scientific application of urea should note the following:
(1) urea for topdressing, both soil applied to the tip of the crop, but also suitable for foliage spraying.
(2) Urea is suitable for foliar spraying of various crops. The appropriate concentration is generally between 0.2% and 2.0%, Urea which varies depending on crop species and growth period. Urea foliage spraying, we must pay attention to the side of the biuret content of less than 0.5%.
(3) urea is not suitable for seed fertilizer, mainly because of high nitrogen content, and the use of seeds at the same time easily lead to missing seedlings and seedlings. Urea Some of the quality of urea is not good, containing a certain amount of biuret on the kind of germination and seedling toxic effects.