1. Largest losses of ammonia occur when urea is surface applied to wet or damp soil surface followed by a period of drying. Up to 22% of applied urea-N can be lost in 1 week. Even if the soil temperatures are cold (e.g. 26-35 °F) growers should avoid applying urea under these conditions!  These conditions occurred in 4 trials which had ammonia-N losses >30% of the application rate.
  2. The 2 applications onto snow had 20-25% cumulative loss.
  3. Applying urea to a dry soil surface is best, but the size of the first precipitation event is critical to defining whether ammonia losses will be small or moderate. At least 0.5” rainfall in a single event is needed to move urea into the soil deep enough to prevent volatilization. Light scattered rain is often not sufficient moisture; it may increase rather than prevent volatilization losses.
  4. Large loss of fertilizer N (e.g. > 30% of applied N rate) can probably be avoided, but losses of 8-15% appear to be quite common in northern Montana. Mid-row or subsurface banding (at least 2" deep) are the best placement methods to minimize losses.
  5. Agrotain® added to urea always reduced losses. It provided two weeks of volatilization protection in acidic soils, but its longevity was considerably greater in calcareous soils (up to eight weeks total).
  6. Seeding after broadcasting urea did not provide sufficient incorporation to mitigate volatilization losses.