- Ammonia losses are largest when urea is surface applied to wet or damp soil surface
followed by drying. Up to 22% of applied urea-N can be lost in 1 week,, > 30% total.
Even if the soil temperatures are cold (e.g. 26-35 °F) growers should avoid applying
urea to wet or damp soil!
- The 2 applications onto snow had 20-25% total loss.
- Applying urea to a dry soil surface is best, but the size of the first precipitation
event is determines the amount of ammonia loss. At least 0.5” rainfall in a single
event is needed to move urea into the soil deep enough to minimize or 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 greater in calcareous soils (up
to eight weeks).
- Airdrill seeding after broadcasting urea did not provide sufficient incorporation
to mitigate volatilization losses.
- Surface broadcast urea for fall-planted crops should be applied in the spring to get
the greatest fertilizer N recovery (percentage of applied N recovered). Fertilizer
N recovery in winter wheat grain averaged 26, 28 and 37% for late-fall, winter, and
spring applications, respectively.
- Late-fall and winter applications are more susceptible than spring applications to
N volatilization loss. The addition of Agrotain® can mitigate N loss by 60-65%.
- Grain protein was higher for spring urea applications than late-fall and winter applications.