Is Urea Safe As a Fertilizer?

Composition

• Urea is preferred to most other nitrogen sources due to its relative ease of manufacture, ease of transportation and higher nitrogen content than other nitrogen-based compounds. Urea contains 46 percent nitrogen, and each ton of urea supplies 35 percent more nitrogen than a ton of ammonium nitrate. Urea is also stable during storage and transportation as opposed to its most commonly used alternative ammonium-nitrate. Ammonium nitrate is classified as hazardous given its use in explosive manufacturing.

Properties

• The outstanding unique property of urea is that the product itself does not contain nitrate-N or ammonium nitrate but converts to ammonium nitrate within two to 10 days of soil application. This conversion is dependent upon soil temperatures and pH levels. In soil with pH levels greater than 7.5, it is possible for the conversion to result in ammonia gas rather than ammonium nitrate. In dry soils, this ammonium gas can be harmful for roots. It is therefore important to make sure that soil conditions are optimal before the application of urea.

Urea Forms

• Urea that is used as fertilizer is available commercially in prills or dry, granulated form. The product was initially obtained by dropping the liquid urea from a prilling tower where the product dried in the process. The resulting prills were smaller and softer than other nitrogen material usually used in fertilizers. Presently, urea is processed in the form of granules that are larger and harder in texture and better resistant to soil moisture, according to the University of Minnesota Extension website.

Advantages

• Urea has a number of advantages over other sources of nitrogen. The product can either be applied to the soil in the form of solid or liquid and can also be applied as a foliar spray when required. As the product decomposes in soil, it produces a very low rate of atmospheric pollutants. Given the high level of nitrogen in urea, crop yields are significantly improved as compared to crops fertilized with other nitrogen sources. The best time to apply urea is when the product will not be exposed to extended period of warm weather conditions.