Fall Application of Anhydrous Ammonia
Key Points
 Anhydrous ammonia is the
recommended N source for fall
application.
 Fall N application should not
begin until daily maximum soil
temperatures at a 4-inch depth
are at 50º F and below.
 Soils at application should be
moist in order for the
applicator knife tracks to seal
properly.
Applying nitrogen (N) in the fall can have some advantages including economic
incentives relative to fertilizer costs, reduced soil compaction, and spreading out the
workload. However, there are some potential disadvantages including the loss of N
between application and crop use and the potential environmental concern of nitrates
leaching into streams, lakes, and groundwater.
Preferred Fall Nitrogen Source
Anhydrous ammonia is the recommended N source for fall application. Upon
application, anhydrous ammonia reacts quickly with water in the soil to form
ammonium. Ammonium is strongly attached to clay and organic matter in the soil, and
is not subject to N loss through volatilization, leaching, or denitrification.
Nitrification is a process in the soil where bacteria convert ammonium to nitrate. The
nitrate form of N is subject to loss by leaching or denitrification. The rate of nitrification is
dependent on soil temperature.
Soil Conditions for Fall Application
Fall applications of anhydrous ammonia should not occur until daily maximum soil
temperatures are at 50º F at a 4-inch depth, and trending downward. The nitrification
 Consider applying some N in
rate (bacteria activity) is significantly reduced at 50º F but microbial activity still occurs
the fall and the remainder in
until soil temperatures are below 32º F.1 Long periods of time at low soil temperatures
but still above 32º F after application, can result in a significant portion of the
the spring which reduces the
ammonium
being converted to nitrate. Consider the use of a nitrification inhibitor, such
potential for overall N loss.
as N-Serve® with fall application. Nitrification inhibitors do not “tie-up ammonium”, but
inhibit the bacteria responsible for converting ammonium to nitrate. Also, fall N
application should not occur on soils that are poorly drained or have excessive drainage, sandy soils, or soils that rarely freeze.1
At application time, soils should be moist in order for the applicator knife tracks to seal properly. Soils that are too dry or too wet at
application may result in ammonia loss as the knife tracks may not seal properly. Also, application depth should be about 6 inches. If
soils are dry at application, consider increasing the application depth to 8 inches which can reduce N loss from volatilization.
Nitrogen Rates and Timing
Consider applying part of your N for each field in the fall and the remainder in the spring in order to minimize the effect of potential
spring N loss. The fall applied N can provide early season N requirements. The remaining N that is spring applied contributes to
increased nitrogen use efficiency and reduces the potential of N loss through leaching or denitrification. Consider using the Corn
Nitrogen Rate Calculator at http://extension.agron.iastate.edu/soilfertility/nrate.aspx to determine an N application rate. The online
tool, developed by midwestern Universities, takes into account previous crop, expected corn price, N price, and geography when
calculating an economic N application rate.
Sources:
1
Fernandez, F.G., E. Nafziger, S.A. Ebelhar and R. G. Hoeft. 2009. Managing nitrogen, Chapter 9, Illinois Agronomy Handbook, C1394. University of Illinois.
http://extension.cropsci.illinois.edu/ (verified 10/22/14); 2 Nafziger, E., 2013. Issues with nitrogen fertilizer: Fall 2013. The Bulletin, Nov 1, 2013. University of Illinois Extension.
http://bulletin.ipm.illinois.edu/ (verified 10/22/14); 3 Fernandez, F. G. 2012. Nitrogen management this fall. The Bulletin, Oct 5, 2012. University of Illinois Extension.
http://bulletin.ipm.illinois.edu/ (verified 10/22/14); 4 2012. Farmers reminded to wait until soil temps are 50 degrees and falling before applying anhydrous ammonia fertilizer. Integrated
Crop Management News. Iowa State University Extension. http://www.extension.iastate.edu/ (verified 10/22/14).
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, soil and
weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. ALWAYS READ AND FOLLOW PESTICIDE
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