Fall Anhydrous Ammonia Application to Dry Soil and N Loss
In the fall of 2011 many areas of the Midwest had dry soils during anhydrous ammonia application. Many of those areas continued
to be very dry through the end of February 2012. In addition, some areas also experienced warm fall and winter weather
conditions. This has led to questions about how much nitrogen (N) may have been lost from the fall application, and how to
determine whether additional N should be applied to help produce a good corn crop in 2012.
Fall Anhydrous Ammonia Applications
Fall anhydrous ammonia applications are common in many areas
largely due to time constraints in the spring and economic
considerations. It helps to spread out the workload so there is
more time to focus on corn planting in the spring. Wet spring
weather can also prevent applying anhydrous ammonia ahead of
corn planting, forcing producers to apply more expensive sources
of N after planting. However, fall applications are considered
riskier than preplant or sidedress applications in terms of N loss
because of the long time between application and when the corn
plant uses the N.1
Fall applications of anhydrous ammonia normally occur on soils
that become cold enough to limit nitrification. The average soil
temperature is recommended to be below 50°F before making
applications in the fall.2 Freezing temperatures and snow will
eventually stop nitrification from occurring. Application to moist
soils helps provide a fast conversion of ammonia to ammonium
which binds to soil particles minimizing N loss through
volatilization.
Dry Soil Conditions at Application
Anhydrous ammonia can be applied on dry soils with limited N
loss as long as the ammonia is applied deep enough to get it in
moisture and the soil is well sealed above the injection slot to
prevent volatilization. Ammonia can move up to 6 inches in very
dry soil, and with shallow placement it could diffuse to the soil
surface and be lost to the atmosphere. Applying to a depth of 8
inches in dry soil is recommended so the ammonia does not
diffuse all the way to the soil surface in search of water.3 If the soil
is cloddy, channels can be present for the ammonia to move
through the soil and escape as gas.
It is very difficult to determine how much ammonia can be lost
through volatilization in dry soil. The best way to determine if loss
occurs is by smell. If the ammonia smell was obvious and
lingered for several hours or more after application, loss probably
occurred.4
The Chemistry of Anhydrous Ammonia
Applied to Soil
1. Anhydrous ammonia is a gas that quickly reacts with
water in the soil to form ammonium.
NH3 (ammonia) + H2O
NH4+ (ammonium) + OH Ammonium-N is bound to clay and organic matter in the
soil, and is not subject to N loss through volatilization,
leaching, or denitrification.
2. Nitrification (microbial process in the soil) converts
ammonium to nitrate, which is available for plant uptake
but is also in a form susceptible to N loss.
NH4 +
NO2 - (nitrite-N)
NO3- (nitrate-N)
The process is soil temperature dependent, where
Nitrosomonas bacteria convert ammonium-N to nitrite-N
and Nitrobacter bacteria convert nitrite-N to nitrate-N in
the presence of oxygen. Nitrification inhibitors like
N-Serve® can slow down this process.
3. Denitrification occurs under anaerobic (lack of soil
oxygen) conditions where soil bacteria convert nitrate-N
to N gases, lost through volatilization.
NO3N2, N2O, NO
Wet soils and warm temperatures promote this process
which, along with leaching, accounts for the majority of
N loss.
Warm Fall and Winter Weather Conditions
There is also the potential for higher N loss following fall
anhydrous ammonia applications because of the warm fall and
winter weather experienced in many areas. N loss can occur by
leaching and denitrification any time after soil temperatures allow
for nitrification of ammonium. At soil temperatures above freezing,
ammonium-N can be converted to nitrate-N by soil microbes.
Nitrification increases as the soil temperature increases. Warm
weather accentuates one of the potential downsides of fall
Continued on next page
1 / 2
Monsanto Technology Development & Agronomy
Fall Anhydrous Ammonia Application to Dry Soil and N Loss
Continued from page 1
application of N in that nitrification can begin earlier and
essentially be complete before the corn crop takes up much N.
More N loss can occur with significant rainfall this spring,
whereas less loss of N can occur with a dry spring. If a
nitrification inhibitor was applied with anhydrous ammonia in the
fall, the potential for N loss could have been reduced by slowing
down the nitrification process.
Will Supplemental N be Necessary?
It is very difficult to determine how much N ends up being lost
after a fall application of anhydrous ammonia. It depends on
many factors including soil type/structure, soil moisture and
condition at application, sustained fall and winter soil
temperatures, spring temperatures, rainfall, days of soil
saturation, and field drainage. Applications of supplemental N
may be warranted if sufficient loss has occurred.
No soil test is ideal for providing information to determine how
much N will be available and whether additional N is needed at
sidedress time. N soil tests such as the pre-sidedress soil
nitrate test (PSNT) can help by analyzing for both nitrate and
ammonium levels.5 The accuracy of the test is highly dependent
upon soil sampling and handling procedures. Although there are
different opinions on the reliability of the PSNT, it is a tool that
gives data when trying to make a difficult decision. If soil N
measurements suggest insufficient N remains from the fall
application, calculations can be made and recommendations
followed to apply additional N.
Chlorophyll meters and aerial images can also be used to detect
N deficiencies in corn. Another approach is to perform strip
applications of additional N in a field to see if there is a response
in corn growth or level of greenness.6 A drawback to these
approaches is that N deficiency detection may not occur until it is
too late for a timely application.
Management
Where deep applications of anhydrous ammonia were made last
fall, at least 30 pounds of N for early season corn growth should
be considered for application through the planter or as a preplant herbicide carrier. If significant N has been lost, then more
N should probably be applied via sidedressing. UAN liquid
solutions can be applied as a band on the surface with drops,
even on fairly large corn. To help minimize volatilization and
maximize effectiveness, rainfall or irrigation is needed to move
UAN and urea into the soil. Up to 30% of the urea could be lost
due to volatilization if no rainfall occurs within two weeks and
temperatures are warm.
Assessing N loss and requirements is not an exact science, but
it can help provide estimates that impact your bottomline.
Growers should pay close attention to those fields that were
fertilized with anhydrous ammonia last fall under dry conditions.
Monitoring early season corn growth will be important to assess
supplemental N application needs.
Sources 1Applying NH3 this fall for 2012 corn crop. 2011. AG
Corn showing N loss from leaching and denitrification of
nitrate-N under wet and saturated soil conditions.
Professional. Kansas State University. November 9, 2011. Online at
http://www.agprofessional.com
2Murrell, S. and Snyder, C. 2006. Fall applied nitrogen in the Corn Belt:
Questions and answers for corn. Online at http://www.ppi-ppic.org
3Anhydrous ammonia and dry soils. 2011. The Bulletin No. 24 article 9/
November 4, 2011. University of Illinois. Online at
http://bulletin.ipm.illinois.edu
4Mengel, D. 2011. Applying anhydrous ammonia under dry soil conditions.
Agronomy e-Updates No. 324, November 4, 2011. Kansas State University
extension. Online at http://www.agronomy.ksu.edu
5Camberato, J., Nielson, R. L. and Joern, B. 2011. Assessing available
nitrogen from fall– and spring-applied nitrogen applications. Corny News
Network May 2011. Purdue University Department of Agronomy. Online at
http://www.kingcorn.org
6Fernandez, F. G. 2011. Sidedressing nitrogen for the corn crop. The
Bulletin No. 11 article 3/June 17, 2011. University of Illinois. Online at
http://bulletin.ipm.illinois.edu
Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may
obtain as local growing conditions, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible.
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Leaf Design℠ is a servicemark of Monsanto Company. All other trademarks are the
property of their respective owners. ©2012 Monsanto Company. 03082012TED
2 / 2
Monsanto Technology Development & Agronomy