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Nitrogen Volatilization
4/25/2003
Ron F. Meyer
Area Extension Agent
(Agronomy)
Colorado State University Extension
Golden Plains
Area |
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Surface application of urea is a common practice used by no-till
farmers. Because the urea is left on the soil surface, there have been many
questions as to how much nitrogen could be lost to volatilization (ammonia loss
from urea converting to ammonium). The urease enzyme is required for this
conversion and is abundant on crop residues. Since a lot of crop residue is
present with no-till, there could be greater nitrogen loss from volatilization
as compared to tilled soils.
When urea is applied to the soil surface,
the fertilizer granules often disappear without a significant precipitation
event. Very small amounts of water (even moisture absorbed from the air) will
dissolve the urea granule. Just because the granules disappear doesn’t
mean the nitrogen is lost. The urea is still present but in a sense has melted
onto the soil surface and is more prone to hydrolysis than if it were still in
the granule form. If significant precipitation (usually regarded as more than
0.25 inch) is received to move the urea into the soil, enough soil particles
are present to lessen ammonia loss.
Because the urea to ammonia
conversion is an enzymatic reaction, the rate of conversion is greater at
warmer temperatures. Since soil temperatures are much lower during the late
fall, surface applications of urea have been recommended. However, fall and
winter months usually have lower precipitation and the urea is more likely to
lie on the surface longer than when applied in the spring.
Urea
application timing studies were conducted on no-till corn in eastern South
Dakota in 1998, 1999, 2000 and 2002. Surface applied urea was applied as per
the timing treatments. For each application timing two rates of nitrogen (50
and 100 lbs N/a) were applied. A check plot without nitrogen also was included.
The average data from the four years are presented.
Nitrogen rate
significantly influenced average grain yield over the four years and yield
increased with each level. Application time also significantly influenced grain
yield. Average grain yields from the late fall and winter applications were
significantly lower than the planting and V6 timings. Loss of nitrate-N to
leaching does not appear to be a contributing factor because departures from
average precipitation for the months April to June were – 4.19 inches
(1998), 1.64 inches (1999), 1.99 inches (2000), and – 2.62 inches
(2002).
Precipitation data was summarized as days after urea application
to the first precipitation event of 0.25 inch or more. As expected, the late
fall and winter applications had the greatest number of days to this first
precipitation event. The fewest days were recorded with the planting and V6
application timings. The longer urea lays on the soil surface, the greater the
chance of ammonia volatilization, especially under moist, warm conditions.
However the temperatures were cooler during the fall and winter applications as
compared to the spring applications. Apparently, low temperature conversion of
urea to ammonia and volatilization can take place although probably very
slowly. Data from Canada indicate if the soil surface is wet and soil
temperature is near 50º F, losses were about 1.5 lb of nitrogen a day. In
the South Dakota studies, the affect that warmer temperature might have had on
nitrogen volatilization was diminished with the occurrence of precipitation
soon after nitrogen application as seen with the planting and V6 application
timings. This data would suggest that nitrogen is lost through volatilization
when significant rainfall after nitrogen application is delayed even if
temperatures are relatively cool.
We appreciate the financial support of
the SD Corn Utilization Council for partial funding of these
studies.
SOURCE:
Anthony Bly, Research Association, Ron Gelderman,
Professor; South Dakota State University |
Page Created and Maintained by: Perry D. Brewer, Area
Extension Agent (Technology Education/Youth)
4/25/2003 |
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