Fall Anhydrous Applications: Do’s and Don’ts

It is much too early to fall apply anhydrous ammonia to meet your 2024 corn nitrogen (N) needs, but there are other factors to consider given our dry soils this fall. 

Several agronomists have noted that earlier than normal corn firing this year was due to the crop running out of N and they think loss of N occurred during application last fall due to anhydrous applications in dry soils that did not seal.  While this is plausible, some soil nitrate may have been leached out in areas with normal or higher rainfall and in other areas dry soil conditions this year may have also led to less nitrogen uptake with limited moisture.

Soil moisture is needed for the organic N to "mineralize", change to ammonium (NH₄⁺) and then to nitrate (NO₃^-). Both forms can be taken up by crops, but some nitrate can be leached out or change to gas N forms with normal or excess rainfall. Applied anhydrous ammonia needs to change into ammonium by soil moisture so it can be available for uptake and held on the soil clay particles and organic matter as ammonium (NH₄⁺). If this process does not happen or happens slowly due to lack of soil moisture, much of the ammonia can be lost at injection because of limited knife track closure. This volatile loss can happen even for a period of time after injection. Once converted to NH₄⁺, a positively charged ion, it will be held on the soil cation exchange and will not move much with water unless it converts into nitrate by soil microorganisms. In the ICM article, Anhydrous Ammonia Application in Dry Soil, John Sawyer discusses concerns about application into dry soils with detail. 

Do’s

If soils are dry after harvest, wait to apply anhydrous ammonia until you get some rain that moistens soil down to 5 or 6 inches to avert ammonia volatilization losses. Additionally, wait until soil temperatures average 50°F and continue to trend lower. This will delay conversion of the ammonium to nitrate and reduce leaching losses with high rainfall in the fall or early spring. Measure soil temperatures at 10 a.m. or 7 p.m. or check the ISU Iowa Environmental Mesonet which now shows past and future trends. It should be noted that nitrification inhibitors are not a substitute for proper placement depth or timing of anhydrous ammonia.

If soil moisture conditions are questionable, make a pass around the field. If you can smell ammonia, make adjustments to equipment or wait until conditions are more suitable.  

Properly maintain and adjust equipment to ensure uniform application. The article Application Checkpoints for Fall Ammonia provides guidance for maximizing application. 

Don’ts

If application causes cloddiness, or large air pockets or lack of covering the knife track during application, stop application and wait for better conditions. While fall application of anhydrous ammonia in good soil conditions rarely causes concerns for seedling damage in the spring, we did see impact of fall 2022 anhydrous application on 2023 planted corn.

Conversely, application under really wet conditions can cause the knife track to smear and some ammonia will volatilize because of inadequate closure of the knife track. Avoid application under too dry or too wet soil conditions.  

Don’t make a shallow application with the idea that any rain we do get will prevent volatilization. Keep application depth at your normal placement depth.

Safety Reminders

Safety when handling and applying anhydrous ammonia is always paramount and has its own checklist of do’s and don’ts. Always be conscious of wind direction when filling tanks, changing tanks and during application. Please review Safety First with Anhydrous Ammonia Applications.

It has turned out to be an early harvest season, but it is too early to apply anhydrous and hopefully our soil moisture conditions will improve so we can appropriately and safely use this source of N this fall.