MSU Extension in Roosevelt County
Reduce Loss of Ammonia Gas from Urea Fertilizer
More urea fertilizer (46-0-0) is applied to farm fields in Montana than all other
nitrogen fertilizers combined, largely due to both cost and availability. However,
urea fertilizer has some potential to 'volatilize' into ammonia gas and escape into
the atmosphere, reducing the nitrogen available for plant uptake. Fortunately, enough
is known about urea volatilization that, through sound management, it may be greatly
minimized.
According to Clain Jones, Montana State University Extension soil fertility specialist
in the Department of Land Resources and Environmental Sciences, "The worst-case scenario
for urea volatilization is to surface broadcast during a warm period on a moist sandy
soil, a grass hay field or a field with a lot of residue." This can be a significant
problem if the urea is not incorporated into the soil with tillage, rainfall or irrigation
within a couple days after application.
"Once urea is about two inches down into the soil, it has little chance of leaving
the soil as ammonia gas," Jones said.
Urea is not the only nitrogen fertilizer that can volatilize. Ammonium sulfate and
liquid nitrogen fertilizers may also volatilize. In addition, anhydrous ammonia can
volatilize if not placed deep enough into the soil or if cracks form above the knife
point. Ammonium nitrate (34-0-0) generally does not volatilize, yet its availability
is limited in many regions in the state.
A large number of research studies that have compared yields between crops applied
with either ammonium nitrate or urea in Montana and Idaho have shown very similar
yields, suggesting minimal losses as ammonia gas from urea. Grant Jackson, professor
at the Western Triangle Agricultural Research Center at Conrad conducted many of the
Montana studies. He said "Growers can expect similar yields from urea as from other
forms of nitrogen fertilizer, and like other nitrogen sources, it needs to be applied
correctly."
"Fortunately, Montana often does not have conditions that cause substantial volatilization,
particularly during the major fertilizer application period from mid Fall to early
Spring," Jones said.
The best ways to prevent urea volatilization are to apply it during cool periods,
or incorporate the fertilizer one or two days after application either with tillage
or with one-half-inch or more of irrigation or rain. Less caution is needed on fine,
textured soils, especially when they have low amounts of crop residue. Jones said
that "Once nitrogen fertilizer is in contact with the soil, it has a much better chance
of staying in the soil than escaping as a gas."
Although there is always a risk of losing nitrogen to the atmosphere, well thought
out planning can greatly minimize the potential for nitrogen loss.
For additional information on how to efficiently manage urea fertilizer, please see
MSU's new regional publication entitled "Management of Urea Fertilizer to Minimize
Volatilization" at http://landresources.montana.edu/SoilFertility/ammonvolat.html or order it from MSU Extension Publications.
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