Fall applications of anhydrous ammonia can help to reduce soil compaction and spread out the workload for more timely spring plantings.
Spring anhydrous ammonia applications can help to limit nitrogen loss before it is needed by the crop.
Splitting applications in the fall and spring can help minimize many of the disadvantages associated with a single application.
Anhydrous ammonia is a good and economical source of nitrogen (N). It is a pressurized liquid that turns into a gaseous form immediately when applied into the soil and quickly reacts with soil water to form ammonium. It binds tightly to the soil, so there is very little movement of the ammonium. Only after nitrification, when the ammonium is converted to nitrate, does it become mobile. Nitrate can be lost from the soil profile via leaching or denitrification. When compared to other N fertilizers, the rate of conversion to nitrate in the soil is slower with anhydrous ammonia, helping to minimize the potential for N loss. Warm temperatures and wet soils speed the nitrification process.
Fall application is appealing as anhydrous ammonia is usually lower in costs, there is more time for application, and better soil conditions. Success of fall applications can be increased by applying once soil temperatures reach 50°F at the 4-inch depth with continuing cooler conditions forecasted, including a nitrification inhibitor, and applying to fields that do not have a history of remaining wet or that drain excessively.
A nitrification inhibitor works best when soils are at or below 50°F, as the inhibitor can be reduced under warm soil conditions as well. The ammonium form is very tightly bound to soil particles, therefore, maintaining the ammonium form as long as possible will help lessen the possibility of loss via nitrate leaching or denitrification.
If conditions are not ideal for a fall application, with warm soil temperatures extending to late fall or wet soil conditions, the window of application may be very small and having an alternative plan that could include split applications can be beneficial. A potential solution may be a fall application on the fields best suited for N retention and delaying application on fields where ammonia is not well suited.
Anhydrous ammonia can be and is often applied in the spring. However, if the planting window opens close to application there are some factors that should be considered as it can injure seeds and seedlings.
If the ammonia has an odor during application, the equipment should be adjusted, or application delayed until soil conditions improve.
Inject the ammonia at a depth of at least 6 to 8 inches, and make sure soil conditions allow for an adequate seal over the injection point. It can move through the soil when the conditions dry, particularly in course soils. Under cloddy conditions it is possible for the ammonia to move up the soil profile and escape.
The use of a sealer attached to the knife can help close the injection opening, and under no-till conditions a coulter in front of the knife may also assist in making an opening so that it will close more completely with the use of a sealer.
Delay planting to reduce the possibility of seed or seedling injury.
What can be done to minimize the possibility of anhydrous ammonia crop injury?
There is not a specific amount of time in which spring applied anhydrous will no longer injury the crop. If planting needs to occur soon after application, there are some recommendations that can be considered. Not planting directly over the injection opening can help reduce the risk. If the planter is equipped with GPS technology, the planter unit can be offset by at least four inches or more, so the seed is not planted over the injection opening. If it is off-set significantly, planting can occur on the same day as application with minimal risk of injury. Applying the ammonia in one direction and planting in the other can also help reduce amount of seed and root contact. Reduce the application rate or narrow the spacing of the knives to lower the ammonia concentration at a single point. Consider applying as a side-dress application, maintaining a safe distance from the seed and developing roots to widen the application window and limit crop injury.
Splitting Fall and Spring Applications
Many of the disadvantages with fall and spring applied anhydrous ammonia can be minimized by applying a lower rate in both the fall and spring. Applying some anhydrous ammonia in the fall, and the rest in spring has the advantage of minimizing the risk of fall-applied N loss. The N applied in the fall can provide what the crop needs to get started in the spring. The remainder applied in the spring, closer to when the plant needs the N, helps to increase use efficiency and reduces the chance of loss by leaching and denitrification.
Timing of Nitrogen Sidedress Applications
1Sawyer. J. 2019. Fall fertilizer nitrogen application. Iowa State University Extension. https://crops.extension.iastate.edu/cropnews/2019/10/fall-fertilizer-nitrogen-application.
2Nafziger, E. 2020. Is fall a good time to apply nitrogen? Department of Crop Sciences, University of Illinois. https://farmdoc.illinois.edu/field-crop-production/is-fall-a-good-time-to-apply-nitrogen.html.
3Sawyer. J. 2019. Anhydrous ammonia application -- spring 2019. Iowa State University Extension. https://crops.extension.iastate.edu/cropnews/2019/03/anhydrous-ammonia-application-spring-2019.