Is it effective to spread urea after rain on a sunny day? Timing the topdressing is key

It is effective to spread urea after rain on a sunny day. But it is recommended to wait three or four days before spreading, because urea is a fertilizer with extremely strong water solubility, and it can even absorb moisture from the air and dissolve, and on top of that it is not easily adsorbed by the soil. If it is spread right after rain, the fertilizer will be lost with the water flow, causing the loss of fertility so that it cannot exert its fertilizing effect, and at the same time it will cause fertilizer damage in low-lying areas.

The ten taboos of using urea

1. Do not mix it with ammonium bicarbonate

After urea is applied to the soil, it must be transformed into ammonia before it can be absorbed by crops, and its transformation speed is much slower under alkaline conditions than under acidic conditions. After ammonium bicarbonate is applied to the soil, it shows an alkaline reaction, with a pH of 8.2 to 8.4. Mixing ammonium bicarbonate and urea in farmland will greatly slow down the speed at which urea is transformed into ammonia, easily causing the loss and volatilization loss of urea. Therefore, urea and ammonium bicarbonate should not be mixed or applied at the same time.

2. Do not broadcast it on the soil surface

When urea is broadcast on the soil surface, at room temperature it takes 4 to 5 days of transformation before it can be utilized, and most of the nitrogen is easily volatilized during the ammonification process. Generally, the actual utilization rate is only about 30%. If it is broadcast on alkaline soil and soil with high organic matter content, the loss of nitrogen will be faster and greater.

Moreover, when urea is applied shallowly, it is easily consumed by weeds. When urea is applied deeply, the fertilizer is blended into the soil, keeping the fertilizer in a moist soil layer, which is conducive to exerting 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 utilize. Experiments have proved that deep application can increase the utilization rate of urea by 10% to 30% compared with shallow application.

3. Do not use it as a seed 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, so it is not suitable as a seed fertilizer. If it must be applied as a seed fertilizer, contact between seeds and fertilizer should be avoided, and the amount used should be controlled.

4. Do not irrigate immediately after application

Urea belongs to amide nitrogen fertilizer. It must be transformed into ammonium nitrogen before it can be absorbed and utilized by crop roots. The transformation process takes a long or short time depending on soil quality, moisture, temperature and other conditions, and generally can be completed only after 2 to 10 days. If irrigation or drainage is carried out immediately after application, or if it is applied to dry land before heavy rain, urea will dissolve in the water and be lost. Generally, in summer and autumn it should be irrigated only 2 to 3 days after application, and in winter and spring it should be watered only 7 to 8 days after application.

5. Do not mix it with alkaline fertilizers or apply them at the same time

After urea is applied, it must be transformed into ammonium nitrogen before it produces a fertilizing effect, and under alkaline conditions most of the ammonium nitrogen will become ammonia gas and volatilize. Therefore, urea cannot be mixed with alkaline fertilizers such as lime, plant ash, and calcium magnesium phosphate, or applied at the same time. 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.

6. Do not apply it to celery

Celery needs a large amount of nitrogen fertilizer as topdressing throughout its growth period, but urea must not be applied. Because when urea is applied as topdressing, celery fibers increase and become coarse, the plants age, growth slows, and when eaten it has a bitter taste and poor quality. Celery is suitable for ammonium bicarbonate, ammonia water and organic fertilizers, which helps improve quality.

7. Do not use too large an amount

Urea has a high nitrogen content, so the application amount should not be too large, so as to avoid unnecessary waste and "fertilizer damage." Generally, 5 to 15 kg is applied per mu, and 15 to 20 kg per mu for paddy fields. If too much is applied, it cannot be absorbed by the soil before being transformed 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 is lost and enters groundwater, which will lead to nitrogen pollution of water bodies, causing the deposition of nitrite and seriously affecting the safety of people and livestock.

8. Do not spray it 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 also poison the plants. Usually, for corn, wheat, rice and cotton, a concentration of 2% is appropriate; for vegetables and melons and fruits, 0.5-1% is more suitable; for fruit trees, 0.5-1.5% is appropriate.

9. Do not apply it too late

Applying urea too late is not conducive to exerting its 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.

10. Do not apply it alone

The effective component of urea is nitrogen, and its nutrients are single, while crop growth and development require multiple nutrients. Therefore, urea should be applied together with organic fertilizers and phosphorus, potassium fertilizers, etc., to meet the needs of crops for various nutrients. Moreover, reasonable mixed application of urea with organic fertilizers and chemical fertilizers can also effectively improve its utilization rate. For example, mixed application of urea and superphosphate can transform unstable ammonium bicarbonate into stable ammonium phosphate, thus greatly reducing the natural volatilization of nitrogen. Mixed application of urea and organic fertilizers produces organic acids during the fermentation process, which can also accelerate the transformation and decomposition of urea, allowing it to be quickly absorbed by crops and improving the utilization rate of urea.

The above is the relevant introduction on whether it is effective to spread urea after rain on a sunny day. I hope it is helpful to everyone.