Fall Application of Anhydrous Ammonia Fertilizer

Key Takeaways

• Anhydrous ammonia is the recommended source of nitrogen for fall applications because the risk of losing nitrogen is reduced compared to applications of other forms of nitrogen fertilizer.
• Applications should be made when soil temperatures are below 50 °F, using a nitrification inhibitor, and when soil conditions are not too wet or too dry.
• Limiting the amount of nitrogen applied in the fall helps to minimize economic and environmental risks.

What Are the Benefits and Risks of Fall Anhydrous Ammonia Applications?

Applying anhydrous ammonia (NH3) in the fall before your next corn crop has advantages. Fall application of nitrogen (N) spreads out the workload, allowing more time to focus on planting in the spring, may reduce soil compaction in the spring, can provide better assurance that N is available if wet conditions in the spring prevent pre-plant application, and potentially can lower fertilizer costs. However, there are disadvantages to fall N application as well.^1,2

Applying N in the fall can be riskier than preplant or in-season sidedress applications because of the potential for N loss between the time of application and crop use. Environmental concerns of nitrate (NO3^-) leaching and runoff into groundwater, ponds and streams also are increased. In some corn producing areas the amount of nitrate in the groundwater or in runoff is a concern, so regulations may prohibit the application of nitrogen fertilizer until a certain calendar date (e.g., November 1) or not allow for fall application at all until the following spring. Be sure to consult with local government agencies in your area that may be responsible for fall/winter nitrogen application regulations.

Chemical Reactions in the Soil after Anhydrous Ammonia Application

The recommended source of N for fall applications is anhydrous ammonia (NH3) because it converts to nitrate (NO3^-) in the soil at a slower rate than other N fertilizers. Anhydrous ammonia fertilizer is a gas with an extremely high attraction to, and quickly reacts with, water in the soil to form ammonium (NH4⁺). Because ammonium is positively charged, it is not subject to N loss because it is bound to negatively charged clay particles and organic matter in the soil.

Nitrification is a two-step microbial process in the soil that converts ammonium to nitrate (NH4⁺ to NO3^-). The nitrate form of N is readily available for plant uptake, but because of its negative charge, it can also be lost through leaching and denitrification. The nitrification process is soil temperature dependent and becomes limited (about 20% of maximum) as soil temperature falls below 50°F. Nitrification continues down to 32 °F, but at a slower rate.

Denitrification is a microbial process that occurs under anaerobic (lack of oxygen) soil conditions where nitrate is lost when it is converted to N gases (N2, N2O, NO) and these gases are lost through volatilization. Warm periods in late winter and early spring allow ammonium to be nitrified to nitrate that can be lost by leaching or by denitrification under wet conditions. It is challenging to determine how risky fall application of N will be. A wet spring will increase the risk of N loss, but if the following spring is dry, there may be minor risk of N loss from a fall application.^1,2

Should You Use a Nitrification Inhibitor with Fall Anhydrous Ammonia?

Nitrification inhibitors can temporarily suppress the activity of soil microorganisms responsible for nitrification, helping retain more fertilizer N in the ammonium form by slowing the conversion to nitrate. Most nitrification inhibitor products can remain effective for at least two weeks with cooler soil temperatures potentially extending the period of efficacy even longer.³

Recommendations for Fall Applications of Anhydrous Ammonia

• Wait until soil temperatures are below 50 °F at a 4-inch depth. Anhydrous ammonia should be applied in late fall after soils cool to 50 °F and continued cool weather is in the forecast.
• Use a nitrification inhibitor to help slow the conversion of ammonium to nitrate.
• Moderate soil moisture conditions are best to make a fertilizer application.
  • Soil conditions at application should not be too wet or too dry but should have enough water to allow the ammonia to spread in the soil and convert to ammonium.
    • Ammonia can be lost through volatilization during and after application if the knife injection slots in the soil do not seal properly. Slots can be very difficult to close when soil is wet.
    • In dry soil, volatilization loss can be minimized by increasing the depth of application to 8 inches. If the soil is cloddy, channels may allow the ammonia to move through the soil and escape as gas.
• Avoid application to soils that are prone to wetness or leaching.
• Sandy soils or those with excessive drainage, soils with high pH, and poorly drained soils are generally considered higher risk for fall N applications and may be poor candidates for fall applied N.^1,4

Minimizing Risk when Applying Anhydrous Ammonia in the Fall

• Consider a split application of N in the fall and spring.
  • This approach can help reduce the amount of fall-applied N loss if soil conditions become conducive to loss.
  • The fall-applied N can provide what the corn crop needs to get started in the spring. The remainder can be applied closer to when the plant N uptake is the greatest and can increase use efficiency because there is less chance for leaching and denitrification.
• Limit fall N applications to only some of your planned corn acres.
  • This practice can help limit the number of acres at risk and balance the convenience of fall N application with the economic and environmental risks.
• Monitor early season corn growth to assess supplemental N application needs.

Safety Reminders when Applying Anhydrous Ammonia

Anhydrous ammonia has an extremely high affinity for water, regardless of whether water is contained in the atmosphere, the soil, or living tissue. It will remove water from any water-containing tissue it contacts and can severely injure skin, eyes, and lungs. Wear proper personal protective equipment (PPE) including eye protection, ammonia impervious clothing, gloves, boots, and respiratory protection.

Sources

¹Fontes, G., Jones, J. and Nafziger, E. 2024. Considerations for fall application of anhydrous ammonia. University of Illinois. https://ilagronomy.info/2024/10/21/considerations-for-fall-application-of-anhydrous-ammonia/.
²Mullen, R. and Florence, D. 2010. Fall application of anhydrous ammonia - A good idea? Agronomic Crops Network. Ohio State University Extension. C.O.R.N. Newsletter 2010-34 https://agcrops.osu.edu/newsletters/2010/34#2
³Ferguson, R., Maharjan, B., Wortmann, C., and Krienke, B. 2019. Nitrogen inhibitors for improved fertilizer use efficiency. University of Nebraska-Lincoln. CropWatch. https://cropwatch.unl.edu/2019/nitrogen-inhibitors-improved-fertilizer-use-efficiency.
⁴Camberato, J. 2021. Fall-applied anhydrous ammonia best practices. Purdue University. https://extension.entm.purdue.edu/newsletters/pestandcrop/article/fall-applied-anhydrous-ammonia-best-practices/
Web sources verified 6/1/2026. 1213_135931