- 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.
- The 2 applications onto snow had 20-25% cumulative loss.
- 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.
- 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.
- 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).
- Seeding after broadcasting urea did not provide sufficient incorporation to mitigate