Agronomy Talk


Published on Tuesday, April 16, 2019


Often, farmers find themselves pressed for time in the spring and are forced into tight windows of operation. One operation that many farmers need to carefully consider is the spring application of anhydrous ammonia. Although it’s possible to apply anhydrous before planting, there are strategies to reduce the risk of injury. Keep in mind that there are many ways to apply nitrogen to a crop in-season, so planting should always take precedence to nitrogen applications. Even if you have pre-paid for your anhydrous, you can still sidedress anhydrous with great success.

What Does Anhydrous Do When Applied to Soils?

When anhydrous is applied to soils, it will diffuse out in a circular pattern, creating a cylindrical band in the soil. Soil type, texture, organic matter and moisture at the time of application will heavily influence the diameter of the band. When the ammonia (NH3) is applied to the soil, it grabs a hydrogen ion from water to become NH4+. This positive charge allows the anhydrous molecule to attach to negatively charged soil particles and limits its movement within the soil profile. Therefore, soils with good moisture can reduce the anhydrous band diameter whereas in very dry soils, the band will likely expand to a greater distance.

Soil texture and organic matter can also affect the size of the anhydrous band, and coarse-textured soils will likely have a larger band. In most cases, the band is around three to four inches in radius from the point of injection, and the ammonia is more concentrated in the center of the band. The band size is why the depth of application in the spring is so important, especially as application timing nears planting. Farmers who are applying anhydrous close to their planting date should place their application deeper, at 8 in. if possible, in order to keep the anhydrous band away from the immediate vicinity of germinating seeds and the seminal root system.

From a timing perspective, applying anhydrous more than three days prior to planting is ideal, but that is not always possible, and there is no hard and fast rule regarding the timing of application prior to planting. In those cases where you are applying anhydrous shortly before the planting pass, depth of application and soil moisture become bigger factors than timing. Always shoot to apply anhydrous at a depth in which soil moisture is available.

Anhydrous Injury

Ammonia in the band of anhydrous can damage seedling roots. If the damaged roots appear desiccated and brown, the seedling likely will not survive. Applying anhydrous at an angle relative to the row reduces the risk that the whole row of seedlings will be damaged as a result of being planted too close to the band.

What Else Can Be Done to Reduce the Risk of Injury?

  • Do not apply to soils that are too wet as it will cause smearing and a lack of closing. This can lead to upward migration of the ammonia gas that moves it closer to the seed and the immediate loss of nitrogen.
  • Cloddy soils at the point of application will also allow the movement of the ammonia gas up through the soil profile and result in loss or even seedling injury.
  • Split your application if possible as full rates at planting create a greater risk for injury. Sidedressing anhydrous is indeed an extra pass across the field, but so is replanting. See graph below.
  • Try to apply at a slight angle to reduce intersection with the row if possible.

Should I Stabilize my Pre-Plant Anhydrous?

The process of converting the NH4+ to NO3- can take many weeks. Depending on your soil health, drainage, temperature, soil structure, and rainfall post application (among other factors), it can take longer than that to convert. You want to have adequate NO3- nitrogen available when the corn plant hits the rapid N uptake phase (about V7) because nitrate N is mobile in soil water and thus, the form of N that is more available for uptake. Keep the following in mind when trying to decide if you should stabilize or not.

  • Nitrogen stabilizers extend the length of time your nitrogen remains in the NH4+ form and can reduce the potential for loss via denitrification or leaching.
  • Using a stabilizer can be beneficial depending on your drainage and soil types. Heavier clay soils and/or soils with limited drainage can benefit from the use of a stabilizer.



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Jim Schwartz

Jim Schwartz

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