By: Fabian Fernandez, Extension nitrogen management specialist

Nitrogen is the nutrient most often deficient for crop production in Minnesota, and its use can result in substantial economic return for farmers. However, when nitrogen inputs exceed crop needs, excessive amounts of nitrate can enter either ground or surface water. By effectively managing nitrogen, growers can produce crops in a more profitable and environmentally-friendly way.

There are many nitrogen fertilizers available on the marketplace, but the three most popular in Minnesota are urea, anhydrous ammonia, and urea ammonium nitrate.

Urea - CO(NH2)2

Urea is the most commonly used nitrogen fertilizer in Minnesota. It is easy to use and transport, and is 46 percent nitrogen, all in the urea form. Urea is very soluble and moves in the soil in any direction water moves.

After application in the soil, the NH2 in urea changes to ammonia, either chemically or by the enzyme urease, and then to ammonium.

The potential for volatilization loss is high with urea if it is not incorporated quickly after surface application. Volatilization can reduce growers’ bottom line and harm the environment. Loss is less likely with winter or early spring applications, but results show that the loss may be substantial if the materials remain on the surface of the soil for several days. Considerable crop residue can also cause volatilization due to the presence of urease in the residue.

Volatilization can be minimized by incorporating the urea three to four inches below the soil surface within a few days of application, either with tillage or rain. Typically, a quarter to a half-inch of rain is needed to move urea down three inches. If urea cannot be incorporated by tillage, it is a good idea to use a urease inhibitor to buy more time for the application to be incorporated by rain. Keep in mind that urease inhibitors typically only last around 10 days before deteriorating.