Nitrogen Use Efficiency, Nitrogen Fertilizers, NUE, Nitrogen and the EnvironmentUAN, urea ammonium nitrate 
Nitrogen Use Efficiency

Nutrient Content, %

Source N P2O5 K2O CaO MgO S Cl Form Cost/lb N
Urea-ammonium nitrate (UAN) 28-32             liquid  

From Havlin, Beaton, Tisdale and Nelson (1999)

Non-pressure N Solutions
Of the liquid N fertilizers used for direct application in the United States, non-pressure N solutions are next to anhydrous NH3 in popularity.  In 1995 usage of N solutions was more than 9.5 million tons, equivalent to approximately 24% of the total N consumed. Some of the reasons for the rapid growth in use of N solutions are:

I .Easier and safer to handle and apply than other N fertilizers (especially NH3)

2. Applied more uniformly and accurately than solid N sources.

3. Many pesticides are compatible with N solutions and both can be applied simultaneously, eliminating one pass across the field.

4. Applied through various types of irrigation systems.

5. Safely transported in pipelines, barges, and railcars, which are less expensive and hazardous than the containers required for anhydrous NH3.

6. Low-cost storage facilities can be used to store them more economically than most other N products.

7. Excellent sources of N for use in formulation of fluid N, P, & and S fertilizers.

8. Lower cost of production than most solid N sources.

N solutions are usually produced from urea, NH4NO3, and water and are referred to as UAN solutions. Each UAN solution has a specific salting-out temperature, which is the temperature below which dissolved salts begin to precipitate out of solution. The salting-out temperature determines the extent to which outside winter storage may be practiced and the time of year at which these solutions may be field applied. Salting-out temperatures vary directly with the concentration of plant nutrients in solution. The most positive feature of non-pressurized solutions is their ease of handling and application. Direct application, either broadcast or band applied, is common. N solutions are often added directly to grasses and small grains. When grass- lands are not dormant, spray applications of UAN can cause foliage scorching. A temporary leaf burn, usually lasting for less than a week, will sometimes occur when broadleaf herbicides and N combinations are sprayed on small grains.