text: Ammonia volatilization reduces the economic efficiency of agricultural cropping systems.  Either yield will be reduced or additional costs will be incurred from additional nitrogen fertilizer. The amount of ammonia volatilization depends on several environmental factors, including temperature, pH, and the soil water content.  Additionally, the amount of surface residue and time between urea application and precipitation are also critical. Generally speaking, volatilization will be lower when urea is applied during the wetter and cooler conditions that generally occur in early spring (March and April). However, drying surface soil and rising temperatures as spring progresses increases the probability of ammonia volatilization. Ideally, a manager should attempt to apply nitrogen immediately before a moderate rain event (0.1 inch), allowing urea to dissolve and move into the soil. However, this is not always possible.  The soil's pH also has a strong effect on the amount of volatilization. Specifically, highly alkaline soils (pH~8.2 or higher) have proven to increase urea hydrolysis. One study has shown complete hydrolysis of urea within two days of application on such soils. In acidic soils (pH 5.2) the urea took twice as long to hydrolyze. Surface residues, such as thatch and plant stubble exhibit increased urease activity.  Soils that have high organic matter content also tend to have higher urease concentrations. More urease results in greater hydrolysis of urea and ammonia volatilization, particularly if urea fails to move into the soil.