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Urea is the most widely used nitrogen fertilizer in agricultural production, but when mixed with other fertilizers, chemical and agronomic principles should be followed to avoid chemical reactions that may reduce fertilizer efficiency or cause toxicity. The following are the main taboos and reasons for mixing urea with other fertilizers:

1. Avoid mixing with alkaline fertilizers for application

After urea is applied to the soil, it hydrolyzes under the action of urease to produce ammonium carbonate, which is then decomposed into ammonia. If mixed with alkaline fertilizers, it will accelerate the volatilization of ammonia and cause nitrogen loss.

Taboo fertilizers: lime, plant ash, calcium magnesium phosphate fertilizer, kiln ash potassium fertilizer, steel slag phosphate fertilizer, etc.

Consequence: After mixing, the pH value increases, ammonia volatilization intensifies, resulting in a significant decrease in fertilizer efficiency.

Suggestion: If combined application is required, the application time should be staggered, with an interval of 3-5 days or more, or layered application (one layer of urea and one layer of alkaline fertilizer) should be used.

2. Avoid mixing and composting with immature organic fertilizers

Untreated organic fertilizers will generate high temperatures and organic acids during the composting process, and microbial activity will be vigorous.

• Consequences:

High temperature will accelerate the decomposition of urea, resulting in ammonia volatilization loss.

Microorganisms will extensively utilize nitrogen in urea for reproduction, temporarily “fixing” nitrogen and reducing the nitrogen supply capacity of crops during the season.

Suggestion: Organic fertilizer should be decomposed before being mixed with urea for application, or used as needed to avoid prolonged composting.

3. Avoid direct contact with seeds (used as seed fertilizer)

Although this is not strictly a ‘mixed application’, in practical operation, fertilizers are often mixed with seeds, which is a major taboo for urea.

• Consequences: Urea has strong hygroscopicity and can take away moisture from seeds when in contact with them. Additionally, the urea containing biuret has a toxic effect on seeds, damaging their protein structure and leading to reduced germination rate, rotting seeds, and dead seedlings.

Suggestion: Urea should be kept 5-10 centimeters away from the seeds or strictly prohibited from being used as seed fertilizer.

4. Avoid long-term mixing with strong acidic fertilizers

If urea is mixed with strong acidic fertilizers and stored for a long time, chemical reactions may occur to produce insoluble substances or cause moisture absorption and clumping.

Taboo fertilizers: superphosphate (especially untreated), heavy superphosphate, etc.

Consequence: After mixing, it is prone to moisture absorption and clumping, leading to deterioration of physical properties and difficulty in application.

Suggestion: If mixing is required, it should be applied as it is mixed and should not be stored for a long time.

5. Avoid mixing and spraying with certain pesticides

When foliar spraying, urea is often mixed with pesticides, but not all pesticides are suitable.

Taboo pesticides: alkaline pesticides such as Bordeaux mixture and stone sulfur mixture; Some fungicides or insecticides that are sensitive to urea.

• Consequences: Alkaline pesticides can cause urea to decompose and produce ammonia, which can burn leaves; Some pesticides may undergo chemical reactions when mixed with urea, reducing their efficacy or causing precipitation.

Suggestion: Before mixing, a small-scale test should be conducted to confirm that there is no precipitation or drug damage before using it on a large scale.

6. Avoid excessive mixing with chlorine containing fertilizers (for chlorine sensitive crops)

Although urea itself does not contain chlorine, a small amount of urea or other impurities may be mixed in during the production process. If mixed excessively with chlorine containing fertilizers (such as ammonium chloride and potassium chloride), it will exacerbate the toxicity to chlorine resistant crops.

Taboo crops: tobacco, potatoes, sweet potatoes, watermelons, grapes, citrus, etc.

Consequence: Accumulation of chloride ions will reduce starch and sugar content, affecting quality; Excessive nitrogen can exacerbate the harm of chlorine.

Suggestion: Chlorine free crops should be treated with urea separately or the amount of chlorine containing fertilizers should be strictly controlled.

7. Summary

The core principles of urea mixed application are: avoiding alkali, preventing heat, planting separately, and applying as mixed. As long as these principles are followed, it is possible to avoid fertilizer efficiency losses and maximize the benefits of fertilizers