Urea is the most widely used nitrogen fertilizer in agricultural production. However, when mixed with other fertilizers for application, it is necessary to follow chemical and agronomic principles to avoid reducing fertilizer efficiency or causing toxicity due to chemical reactions. 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 into ammonium carbonate under the action of urease, and then decomposes into ammonia. If mixed with alkaline fertilizers, it will accelerate the volatilization of ammonia, resulting in nitrogen loss.
• Forbidden 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.
• Recommendation: If combined application is necessary, the application times should be staggered with an interval of at least 3-5 days, or layered application (one layer of urea, one layer of alkaline fertilizer) can be adopted.
2. Avoid mixing and composting with unripe organic fertilizer
During the composting process, unripe organic fertilizer will generate high temperatures and organic acids, accompanied by vigorous microbial activity.
• Consequence:
◦ High temperature will accelerate the decomposition of urea, resulting in ammonia volatilization loss.
Microorganisms will utilize a large amount of nitrogen from urea for reproduction, temporarily “fixing” the nitrogen and reducing the nitrogen supply capacity of the current crop.
• Recommendation: Organic fertilizer should be fully decomposed before being mixed with urea for application, or applied immediately after mixing to avoid prolonged composting.
3. Avoid direct contact with seeds (as seed fertilizer)
Although this is not strictly “mixed fertilization”, in practical operations, fertilizers are often mixed with seeds, which is a major taboo for urea.
• Consequences: Urea has strong moisture absorption capacity. When it comes into contact with seeds, it can absorb moisture from the seeds. Additionally, the biuret contained in urea is toxic to seeds, damaging the protein structure of the seeds and leading to reduced germination rates, seed rot, and seedling death.
• Recommendation: Urea should be kept at a distance of 5-10 cm from seeds, or it should be strictly prohibited from being used as seed fertilizer.
4. Avoid long-term mixing with strongly acidic fertilizers
When urea is mixed with strong acidic fertilizers, if stored for a long time, it may undergo chemical reactions, resulting in the formation of insoluble substances or causing moisture absorption and agglomeration.
• Prohibited fertilizers: superphosphate (especially untreated ones), triple superphosphate, etc.
• Consequence: After mixing, it is prone to moisture absorption and caking, leading to deterioration of physical properties and difficulty in application.
• Recommendation: If mixing is necessary, it should be applied immediately after mixing and not stored for long periods.
5. Avoid spraying in combination with certain pesticides
When conducting foliar spraying, urea is often mixed with pesticides, but not all pesticides are suitable.
• Prohibited pesticides: Alkaline pesticides such as Bordeaux mixture and sulfuric acid; certain fungicides or insecticides that are sensitive to urea.
• Consequences: Alkaline pesticides can decompose urea, releasing ammonia gas which can burn leaves; some pesticides may undergo chemical reactions when mixed with urea, reducing efficacy or producing precipitates.
• Recommendation: Before mixing and using, conduct a small-scale test to ensure there is no sedimentation or phytotoxicity, and then apply it on a larger scale.
6. Avoid excessive mixing with chlorine-containing fertilizers (for chlorine-sensitive crops)
Although urea itself does not contain chlorine, a small amount of biuret or other impurities may be mixed in during the production process. If it is mixed with chlorine-containing fertilizers (such as ammonium chloride and potassium chloride) and applied excessively, it will aggravate the toxicity to chlorine-sensitive crops.
• Prohibited crops: tobacco, potato, sweet potato, watermelon, grape, citrus, etc.
• Consequence: Accumulation of chloride ions can reduce the content of starch and sugar, affecting quality; excessive nitrogen can exacerbate the harmful effects of chlorine.
• Recommendation: Urea should be applied separately to chlorine-sensitive crops, or the amount of chlorine-containing fertilizers should be strictly controlled.
7. Summary
The core principles of urea mixed fertilization are: avoid alkalinity, prevent heat, separate species, and apply immediately after mixing. By adhering to these principles, fertilizer efficiency loss can be avoided, and the maximum benefit of the fertilizer can be realized.
Post time: Jan-19-2026