April - June 2005
Forage Systems Update
Vol 14, No. 2
Field Notes from Valerie Tate
At present, ammonium nitrate is the nitrogen fertilizer source of
choice for application to established forages. Urea is another
readily available nitrogen source, but it must be incorporated quickly
with tillage or significant rainfall to avoid volatilization.
Volatilization is the loss of the nitrogen as ammonia, into the
atmosphere. Some of the factors that affect urea volatilization
include soil temperature, soil moisture and soil pH. As soil
temperature increases volatilization increases; as soil moisture
increases, volatilization increases; and as soil pH increases, urea
volatilization increases.
With the looming questions regarding the future availability of
ammonium nitrate fertilizer, Dr. Rob Kallenbach is addressing nitrogen
fertilizer options for established forage stands. Nitrogen fertilizer
sources, including ammonium nitrate, untreated urea, urea treated with
several different stabilization products, and ammonium sulfate, will
be evaluated at FSRC and Southwest Center in Mount Vernon, Missouri.
Both spring and fall applied nitrogen will be applied to tall fescue
and yield measurements will be collected. I will be sure to keep you
informed on the progress and results of this study through our
newsletter.
The following is an excerpt from Dr. Kallenbach's proposal explaining
the rational and importance of this project:
Tall fescue grows on more than 12 million acres and provides forage
for more than 4 million beef cattle in Missouri. Tall fescue-based
pastures cover more acres of farmland in Missouri than any other crop.
It is a popular forage with beef producers because it persists well on
infertile, poorly drained, sloped, and/or unmanaged pastures.
About one-half of all tall fescue acres receive some nitrogen
fertilizer in spring. Most of these applications are made in March or
early April. Another time in which tall fescue acres are fertilized
with nitrogen is in late-summer for stockpiling. Stockpiling tall
fescue allows producers to extend the grazing season into winter and
thereby cut winter feeding costs up to 70%.
In past years, ammonium nitrate has been the most popular source of N
for spring and late-summer fertilization of pastures. Ammonium
nitrate is widely considered the "safest" source of N for forage
production, particularly for late-summer applications, as the N in
ammonium nitrate is much less likely to be lost to volatilization than
is urea. However, ammonium nitrate has become a homeland security
issue for the fertilizer industry because it can be used as an
explosive (Anon., 2004). Additionally, few new ammonium nitrate plants
have been constructed in the United States over the last 20 years, and
given the current economic and security climate, domestic production
is likely to decline over the next 10 to 20 years. These factors are
making ammonium nitrate more expensive than other N sources.
Given the pricing structure and potential problems with ammonium
nitrate, urea is quickly becoming the most widely used N source for
forage production. This is due to urea's wider availability and lower
cost per N unit when compared to ammonium nitrate. In fact, in many
rural parts of Missouri the only source of N available for pastures is
urea. While urea is a common source of N fertilizer for spring
applications, its use for fertilization of pastures is problematic due
to excessive nitrogen volatilization. Up to 40% of the N applied to
pastures as urea can be lost through volatilization if rainfall does
not occur within 48 hours of an application (Lightner et al., 1990).
Given these problems, farmers are looking for a reliable and
inexpensive source of N for pastures.
Several companies have developed products reported to reduce or
eliminate volatilization of urea under field conditions. While the
technology behind these "urea stabilization products" varies, there
has been little "head-to-head" testing under typical field conditions.
Technologies that allow safe application of urea would alleviate
concerns from farmers and the fertilizer industry, but research is
needed to determine which of these products would be most useful for
fertilizing pastures in Missouri.
The overall objective is to develop research-based recommendations
that help industry personnel and farmers determine which urea
stabilization products work best when fertilizing tall fescue
pastures. Specific objectives are:
Objective 1: Compare the efficacy of several urea
stabilization products to ammonium nitrate and untreated urea as a
source of nitrogen for both spring (typically for hay) and late-summer
(stockpiling) N applications to tall fescue pastures.
Objective 2: Determine the optimum rate and use
efficiency for each source of N tested.
FSRC Weather Data. January-March, 2005.
| |
Precipitation (inches) |
20 yr avg. precipitation(inches) |
Observed max. Temp
(°F) |
Observed min. Temp
(°F) |
Average max. Temp
(°F) |
Average min. Temp
(°F) |
Average Bare Soil Temp at 2" depth
(°F) |
| January |
2.01 |
1.05 |
60 |
1 |
35 |
21 |
32 |
| February |
2.77 |
1.12 |
61 |
9 |
46 |
27 |
38 |
| March |
1.22 |
2.48 |
76 |
16 |
53 |
29 |
43 |
| Yearly |
6.00 |
4.65 |
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