Six Tips for Effective Anhydrous Ammonia Applications
Applying nitrogen fertilizer in the fall can help save time, money, and added stress during a busy spring planting season. However, effective applications cannot be planned without proper preparation. Soil and field conditions must be strongly considered before applying anhydrous ammonia (NH₃) to ensure its effectiveness and to protect against nitrogen loss.
Benefits of fall-applied anhydrous ammonia
One of the key benefits of using anhydrous ammonia is that it can be applied in a concentrated band below the soil surface. Research in Western Canada has shown that banding nitrogen fertilizer can improve nitrogen use efficiency by reducing the risk of loss and minimizing the risk of tie-up.
To get the greatest benefit from fall-applied ammonia, applications must be made under the right soil conditions using sound management practices. The following six recommendations can help improve your fall applications this season.
Figure 1: Summary of 106 site years of data in Western Canada showing the right place to apply nitrogen. Source: Rennie, Doyle, & Cowell. (1993). Summary of Western Canadian research.
1. The cooler the soil, the better
Soil temperature is critical to effective anhydrous ammonia applications. When anhydrous ammonia applications occur, the ammonia quickly dissolves in soil water to form ammonium. The ammonium can then be oxidized by certain bacteria into nitrate in a process known as nitrification. While both ammonium and nitrate can be used by growing crops, nitrates have a higher risk of loss through leaching and denitrification—which makes it beneficial to slow down its conversion in the soil.
When soils are cooler, microorganisms will convert ammonia into nitrate-nitrogen at a much slower rate—reducing the likelihood of nitrogen loss and protecting your nitrogen investment.¹ Best practices suggest beginning anhydrous ammonia applications once soil temperature is below 50°F (10°C). Cooler soil temperatures will help slow down the process of nitrification and reduce the potential for nitrogen loss. Soil temperatures should be based on a soil depth of three to four inches (the depth of fertilizer application) and the soil should be on a cooling trend before application.²
Figure 2: Impact of anhydrous ammonia application timing on wheat yields in two locations in Saskatchewan, demonstrating that the loss of nitrogen applied as ammonia in the fall can be minimal when applied to cool soils. Source: Karamanos, Hanson, & Stevenson. (2014).
2. Consider soil moisture and recent weather conditions
Soil moisture is one of the most important factors to consider when it comes to effective anhydrous ammonia applications. While anhydrous ammonia does dissolve readily in water, it is held in the soil by clay and organic matter. Before this hold occurs, the ammonia must dissolve in soil water to form ammonium. Ammonium (NH4+), which has a positive charge, will bind with the negative charge of surface clay and organic matter.
Extremely dry soils may not be ideal for ammonia applications for two important reasons. First, it takes very little soil water to dissolve applied ammonia. But, when soils are extremely dry, the rate at which ammonium binds to the soil exchange sites will be slower because of low moisture.² This can lead to lower levels of plant-available nitrogen in the soil.
Second, and perhaps most important, extremely dry soils may not be capable of creating an effective seal over the top of a band of ammonia. This allows the direct loss of ammonia from the furrow which can lead to significant nitrogen loss and additional time, money, and effort. Ensuring that the soil has available moisture and good structure to flow over and seal the fertilizer band will help reduce the potential for loss and make a more effective anhydrous ammonia application this season. Even a small amount of rainfall or conserved soil moisture can improve soil conditions enough to create a more effective application.²
Figure 3: Average nitrogen loss from different fertilizer sources in Winnipeg and Brandon, demonstrating the impact of soil conditions and moisture on nitrogen loss.
Pro Tip: Check to make sure you are leaving a well-sealed band behind your applicator or you may incur large losses at the time of application.
3. Use a nitrification inhibitor
When added to nitrogen-based fertilizers, nitrification inhibitors slow down the conversion of ammonium to nitrate soon after application.¹ Slowing down this process is important if you want to start applying anhydrous ammonia before the soil has cooled below 10°C (50°F) in the fall. Nitrification inhibitors are important tools that protect nitrogen investments, reduce nitrate leaching, decrease nitrogen gas emissions, and improve nitrogen use efficiency, regardless of whether you apply it in the spring or fall.
However, it should be noted that the loss of ammonia from a band due to denitrification tends to be small—less than two percent and often close to zero. It is also important to note that inhibitors that slow the formation of nitrates will only work in the fall. By spring, the inhibitors will have degraded and won’t further prevent nitrates. Research in wet, heavy clay soils in Manitoba showed that the total nitrogen loss of a nitrous oxide gas was very small and would not likely contribute to yield loss. Overall, the best use of nitrification inhibitors will be for ammonia applications in the early fall and if soils are likely to be very wet or flooded in spring. This can be countered by avoiding these soil types in early fall ammonia application.
Pro Tip: If you anticipate a field may be wet in spring (low lying areas or heavy textured soils), a nitrification inhibitor can help reduce the formation of nitrates that are at risk of loss through denitrification or leaching in the spring.
4. Perfect the application seal
With the right soil and environmental conditions in place to apply anhydrous ammonia, it is time to perfect the seal. When applying anhydrous ammonia to the field, you want to do everything you can to avoid loss. Achieving a perfect seal on the application slot supports this and allows you to avoid the direct loss of ammonia through volatilization (loss to the air). ¹
Pro Tip: A good soil seal over a band requires good soil structure and surface moisture. Avoid topsoil compaction and unneeded tillage to improve ammonia applications.
5. Choose the right application equipment
Good ammonia applications require an applicator capable of creating a well-sealed band at an appropriate depth. Applicators and machines that are not level or contain various banding depths may create a poor band, even in good soil conditions.
Pro Tip: Some application equipment and machines will have harrows or row packers to help seal a band. Be sure that these are positively impacting the condition of your field.
6. Use the right band depth
Ammonia is a gas that is capable of expanding beyond its point of application. If it is poorly sealed during application, it will continue to move to the soil surface and risk loss. Thus, the depth of your band is extremely important for effective anhydrous ammonia applications. In good soil conditions, the band should be eight to 10 cm deep before sealing.
Figure 4: The total percent of nitrogen lost as ammonia over 25 days with different band depths. Source: Rochette, et al. (2013).
It’s Time to Minimize Loss
Following these tips will help reduce nitrogen loss, increase plant uptake, and make more effective annual anhydrous ammonia applications—helping to create a more productive and profitable nutrient management plan.
Learn more about anhydrous ammonia and how to make effective applications with the following eKonomics resources:
Fall Anhydrous Ammonia (82-0-0) Use On Dry Soil –
Nitrogen Application Calculators For Stronger Nutrient Management
Next on Nitrogen: Fall Applications and Smart Sources
Managing Nitrogen Inputs For South/Central Plains Winter Crops
Proper 4R Practices Can Lessen Ammonia Toxicity in Roots
Fall Anhydrous Ammonia Application Tips
Sources:
¹Fall-applied Anhydrous Ammonia Best Practices | Purdue University Pest&Crop newsletter
²Fall Anhydrous Ammonia Applications: What to know about soil moisture | Integrated Crop Management
