How to apply urea correctly? Keep these eight taboos in mind
1. It should not be mixed or applied at the same time as alkaline fertilizers. After urea is applied, it must be converted into ammoniacal nitrogen before it produces a fertilizing effect, and under alkaline conditions most of the ammoniacal nitrogen in ammoniacal nitrogen will turn into ammonia gas and volatilize away, so urea cannot be mixed or applied at the same time as alkaline fertilizers such as lime, plant ash, and calcium magnesium phosphate fertilizer. Generally speaking, in summer and autumn, urea and alkaline fertilizers should be applied 3 to 4 days apart, and in winter and spring they should be applied 7 to 8 days apart.
2. It should not be used as a seed-mixing fertilizer. During the production process, urea often produces a small amount of biuret, and when the biuret content exceeds 2%, it will poison seeds and seedlings. Such urea entering seeds and seedlings will denature proteins and affect seed germination and seedling growth, so it should not be used as a seed fertilizer. If it must be applied as a seed fertilizer, contact between seeds and fertilizer should be avoided, and the dosage should be controlled.
3. It should not be irrigated immediately after application. Urea is an amide-form nitrogen fertilizer. It must be converted into ammoniacal nitrogen before it can be absorbed and used by crop roots. The conversion process takes different lengths of time depending on soil quality, moisture, temperature, and other conditions, generally taking 2 to 10 days to complete. If irrigation or drainage is carried out immediately after application, or if it is applied before heavy rain in dry land, urea will dissolve in water and be lost. Generally, in summer and autumn, irrigation should be carried out only 2 to 3 days after application, and in winter and spring, irrigation should be carried out 7 to 8 days after application.
4. It should not be broadcast on the soil surface. When urea is broadcast on the soil surface, it takes 4 to 5 days of conversion at normal temperature before it can be used, and most of the nitrogen is likely to volatilize during ammonification. The actual utilization rate is generally only about 30%. If it is broadcast on alkaline soil and soil with high organic matter content, nitrogen loss will be faster and greater. Moreover, shallow application of urea makes it easy for weeds to consume it. Deep application of urea integrates the fertilizer into the soil, keeping the fertilizer in a moist soil layer, which is conducive to giving play to the fertilizing effect. As a topdressing, it should be applied in holes beside the seedlings or in furrows at the side of the seedlings, with a depth of about 10 to 15 cm. In this way, urea is concentrated in the dense root layer, making it easy for crops to absorb and use. Experiments have shown that deep application can increase the utilization rate of urea by 10% to 30% compared with shallow application.
5. The dosage should not be too large. Urea has a high nitrogen content, and the application amount should not be too large, so as to avoid unnecessary waste and "fertilizer damage." Generally, 5 to 15 kg per mu is applied, and 15 to 20 kg per mu is applied in paddy fields. If too much is applied, it cannot be absorbed by the soil before being converted into ammonium bicarbonate, is easily leached away by rainwater, and easily harms crops. At the same time, if too much urea is applied, most of it will be lost and enter groundwater, which will cause nitrogen pollution of water bodies, cause nitrite deposition, and seriously affect the safety of humans and livestock.
6. It should not be sprayed on leaves at high concentration. Among all nitrogen fertilizers, urea is the most ideal foliar fertilizer. When urea is sprayed, the amount and speed of protein synthesis by crops exceed those of other nitrogen fertilizers. However, when spraying on leaves, the concentration of the urea solution must not be too high, otherwise it will burn the leaves and also poison the plants. Usually, for corn, rice, and others, the suitable spraying concentration is 2%; for vegetables and melons, 0.5% to 1.5% is suitable.
7. It should not be applied too late. Applying urea too late is not conducive to giving play to the fertilizing effect and easily causes crops to remain green and mature late, so it should generally be applied 4 to 7 days earlier than other nitrogen fertilizers.
8. It should not be applied to celery. Celery requires a large amount of nitrogen fertilizer as topdressing throughout its entire growth period, but urea must not be applied. This is because topdressing with urea will increase and thicken celery fibers, age the plants, slow growth, and give it a bitter taste when eaten, resulting in poor quality. Wang Aiping