How should urea be applied correctly? Remember these seven precautions

1. It should not be mixed or applied at the same time as alkaline fertilizers

After application, urea 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-dressing fertilizer

During the production process of urea, a small amount of biuret is often produced. When the biuret content exceeds 2%, it will poison seeds and seedlings. When such urea enters seeds and seedlings, it will denature proteins and affect seed germination and seedling growth.

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 varies in duration depending on soil texture, moisture, temperature, and other conditions, and generally takes 2 to 10 days to complete. If it is irrigated immediately after application or applied before heavy rain in dryland, urea will dissolve in water and be lost. Generally, in summer and autumn, irrigation should be done 2 to 3 days after application, and in winter and spring, irrigation should be done 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 room temperature before it can be used, and most of the nitrogen is easily volatilized during ammonification, with the actual utilization rate 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 exerting the fertilizing effect. When used as a topdressing, it should be applied in holes beside the seedlings or in furrows at the side of the seedlings, at a depth of 10 to 15 cm. Tests have shown that deep application of urea in the dense root layer facilitates crop absorption and utilization and can increase the utilization rate by 10% to 30% compared with shallow application.

5. The dosage should not be too large

Urea has a high nitrogen content. Generally, 5 to 15 kg per mu is applied in field fields, and 15 to 20 kg per mu in paddy fields. If applied too much, it cannot be absorbed by the soil before it transforms into ammonium bicarbonate. On the one hand, it is easily leached away by rainwater and harms crops; on the other hand, it can enter groundwater, causing nitrogen pollution of water bodies and causing nitrite deposition, seriously affecting 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 urea solution concentration must never be too high, otherwise it will burn the leaves and poison the plants.

7. It should not be applied too late

Applying urea too late is not conducive to exerting the fertilizing effect and easily causes crops to stay green and mature late, so it should generally be applied 4 to 7 days earlier than other nitrogen fertilizers.