Urea is a widely used and highly efficient nitrogen fertilizer that is popular among farmers due to its ease of application. It can be applied as a base fertilizer, top-dressing, or even as a foliar spray. However, improper use can lead to wasted resources and even harm crops, causing what is known as "fertilizer burn." To ensure optimal results, it's essential to follow eight important guidelines when applying urea.
First, avoid mixing urea with alkaline fertilizers such as wood ash, lime, calcium magnesium phosphate, or slag phosphate. When combined, urea can release ammonia gas, leading to significant nitrogen loss. In summer and autumn, it's recommended to separate the application by 3–4 days, while in winter and spring, a gap of 7–8 days is advised.
Second, do not use urea directly as a seed fertilizer. The presence of biuret in urea can be toxic to seeds, reducing germination rates and harming young plants. If necessary, apply it away from the seeds and limit the quantity to prevent damage.
Third, don’t water immediately after applying urea. Urea has low adsorption capacity and can leach easily into the soil. Watering too soon may wash away the nutrients before they are fully absorbed. In summer and autumn, wait 2–3 days before watering, and in winter and spring, wait 7–8 days. For rice fields, maintain a shallow water layer and avoid heavy rain after application.
Fourth, avoid shallow placement. Urea tends to volatilize quickly if left on the surface and can be consumed by weeds. Deep application—about 10–15 cm deep—helps retain the fertilizer in moist soil, improving its effectiveness. Apply it near the base of the plants or in furrows for better root absorption.
Fifth, don’t over-apply. With a nitrogen content of 44–48%, urea is very concentrated. Overuse can cause waste and crop damage. For dry fields, apply 5–15 kg per acre, and for paddy fields, 15–20 kg per acre is generally sufficient.
Sixth, avoid high-concentration foliar sprays. A concentration that’s too strong can burn leaves and harm the plant. For crops like corn, wheat, rice, and cotton, a 2% solution is safe. For vegetables and fruits, 0.5–1% is ideal, and for fruit trees, 0.5–1.5% is recommended.
Seventh, don’t apply urea too late. Late application reduces its effectiveness and can cause excessive vegetative growth, delaying maturity. It’s best to apply urea 4–7 days earlier than other nitrogen fertilizers.
Eighth, avoid using urea alone. It should be combined with organic manure, phosphorus, and potassium fertilizers to provide balanced nutrition. Mixing urea with superphosphate helps convert unstable ammonium bisulfate into stable ammonium phosphate, which enhances nitrogen availability and improves fertilizer efficiency.
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