Montana grain growers annually seed over 5 million acres of wheat with production averaging approximately 15 million bushels (1998-2007). Nitrogen is the primary nutrient that limits wheat production on this land. Hence N fertilization is essential for sustaining yields as well as ensuring our state’s reputation for producing high quality/protein grain. To meet this challenge Montana wheat growers apply N fertilizer to their fields. Most frequently this is achieved through broadcast applications of urea-N (46-0-0) to the soil surface with applications occurring between October and early May. Surface urea applications are susceptible to ammonia volatilization losses if not incorporated with tillage or by rainfall. This process is well known and is summarized by the reactions below.
A number of environmental and soil related factors interact together to affect this process and define the magnitude of loss. Most research shows that losses are enhanced by high soil pH, warm temperatures, light rains sufficient to moisten the soil surface but insufficient to enable movement of urea below the soil surface, and no till management (Jones et al., 2007). No till systems have been reported to enhance volatilization losses of urea because tillage is not present to incorporate urea fertilizer granules into the soil. Also, the urease enzyme necessary for hydrolysis of urea (see reaction above) is particularly active in crop residues that accumulate at the soil surface under no till.