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The application of urea (urea) is the most common nitrogen fertilizer application method in agricultural production, but the chemical properties of urea (such as easy hydrolysis, volatility, and strong moisture absorption) determine strict technical requirements for its application. If applied improperly, it can not only cause fertilizer waste, but also lead to crop burning, late ripening or quality decline. The following are key precautions for applying urea for reference:

1. Deep soil cover (core measure)

After urea is applied to the soil, it rapidly hydrolyzes under the action of urease to produce ammonium carbonate, which is then decomposed into ammonia gas (NH3). If the surface is not covered with soil, ammonia is easily volatile, causing nitrogen loss.

Dryland: It must be deeply applied, preferably 10-15 centimeters deep, and immediately covered with soil after application.

• Paddy fields: Urea should be sprayed and plowed into the soil before watering, or sprayed in shallow water and combined with tillage to mix fertilizer into the mud. Do not spread it on the surface of deep water layers, otherwise urea will be lost with water or undergo denitrification under anaerobic conditions.

2. Avoid “spraying with water”

Many farmers are accustomed to spreading urea on the soil surface and flooding it with water, which is wrong.

Urea is an amide nitrogen fertilizer. Before it is converted into ammonium nitrogen, soil colloids have weak adsorption capacity for it and are easily lost with water.

If it is necessary to apply with water, the amount of irrigation should be controlled, using a “small amount multiple times” method, and middle plowing should be carried out when the soil is slightly dry after fertilization to reduce volatilization.

3. Control the application period (early application)

After urea is applied to the soil, it needs to be converted into ammonium nitrogen by urease for the crop roots to absorb a large amount. The conversion process is affected by temperature:

Temperature 10 ℃: Conversion takes 7-10 days.

Temperature of 20 ℃: Conversion takes 4-5 days.

Temperature of 30 ℃: Conversion only takes 2 days.
Therefore, the application time of urea should be 4-7 days earlier than other ammonium nitrogen fertilizers (such as ammonium bicarbonate) to ensure that the peak period of crop fertilizer demand coincides with the peak period of fertilizer supply.

4. It is strictly prohibited to apply foliar sprays with excessively high concentrations

Urea molecules have a small volume and certain hygroscopicity, making it an ideal raw material for foliar fertilizers. But excessive concentration can burn the leaves, leading to ‘burning seedlings’.

Vegetables and fruit trees: The spraying concentration is generally controlled between 0.5% and 1.0%.

Field crops (rice, wheat): The concentration can be controlled between 1.5% and 2.0%.

Attention: Spraying should be avoided during high temperature periods (such as noon) to prevent rapid evaporation of water, which can cause an instantaneous increase in concentration and burn the leaves.

5. Avoid mixing with alkaline fertilizers

Mixing urea with alkaline fertilizers (such as lime, plant ash, calcium magnesium phosphate fertilizers, etc.) can accelerate the decomposition of urea and the volatilization of ammonia, resulting in nitrogen loss.

If combined application is required, the application time should be staggered, with an interval of 3-5 days or more.

6. Avoid using as seed fertilizer

Urea contains biuret and has strong hygroscopicity. If in direct contact with seeds, it will damage the protein structure of the seeds, causing them to lose their germination ability, or leading to root rot or dead seedlings after emergence.

If it must be used as seed fertilizer, the amount should be strictly controlled and the fertilizer should be kept at a certain distance from the seeds (usually 5-10 centimeters).

7. Prevent excessive use of biuret

Biuret is a byproduct of urea production and has toxic effects on crops.

When purchasing urea, the product label should be checked to ensure that the urea content meets the national standard (generally required to be ≤ 1.0%).

Long term use of urea that exceeds the limit of urea can cause crop leaves to curl, turn yellow, hinder growth, and even lead to death.

8. Cooperate with the application of phosphorus and potassium fertilizers

Urea belongs to high nitrogen fertilizers, and excessive application can lead to nutritional imbalance in crops, manifested as overgrowth, poor lodging resistance, susceptibility to pests and diseases, and late ripening.

According to the fertilizer requirements of crops, phosphorus, potassium fertilizers, and trace elements should be applied in combination to improve fertilizer utilization efficiency and crop yield.

summary

The core principles of applying urea are: deep soil cover, early application, strict concentration control, and avoidance of alkali and harm. Only through scientific and rational application can urea maximize its fertilizer efficiency and achieve high crop yield and quality.