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How to Apply Springtime Anhydrous Ammonia

It can be done, but don’t apply it in wet soils.

Wondering what to do if you couldn’t apply your anhydrous ammonia last fall? Here are some ideas from agronomists at Wyffels Hybrids. 

Last year’s wet fall prevented anhydrous applications and fieldwork, making for a large preplanting workload this spring. Farmers hoping to save time will be asking how soon corn can be planted following a spring anhydrous application. Unfortunately, there is no magic number of days to wait to avoid injury. Time will help, but it won’t prevent injury.

Why Corn Injury Occurs

When farmers inject anhydrous ammonia into the soil and the knife track is properly sealed, it diffuses within the first 24 hours into a 5- to 6-inch-diameter cylinder around the injection point. This diameter is larger in sandy or dry soils. If corn contacts this concentrated zone of ammonia, injury will occur because ammonia is a desiccant and rapidly dehydrates (burns) corn roots.

Injured roots from anhydrous ammonia will appear burnt typically at the tips. Above-ground symptoms include uneven emergence and short, pale plants. Injury is detected more often in dry weather because roots are slow to develop and injured roots limit water uptake. Over time, ammonia converts into a safe, plant available nitrate form. 

Proximity of ammonia band to seed 

One way to avoid corn injury from anhydrous ammonia is to plant corn several inches away from the anhydrous ammonia injection zone. GPS guidance systems can be used to offset planter rows 4 to 6 inches or more from ammonia injection tracks. Make sure the soil is not wet when applying anhydrous in order to avoid compacting future corn rows. Planting can occur the same day as anhydrous application using this method.

Another popular method is to apply anhydrous ammonia at an angle to corn planting. If injury occurs, it only affects a few plants vs. every plant down the row. Injured plants located over the anhydrous track will often appear paler green and shorter compared with plants in between the anhydrous tracks.

Inject anhydrous ammonia 7 to 8 inches deep to minimize potential injury. It’s still not recommended to plant directly down the anhydrous track even at this depth, as corn roots will eventually reach the concentrated ammonia and risk injury. Wet soils at application may smear the sides of the knife track, causing the ammonia band to move up the injection furrow and become highly concentrated near seed placement. If large dirt clods are formed after application, ammonia will seep through the open-air voids and move closer to seed placement.

Nitrogen Rate

Lower N rates minimize risk of injury. An experiment conducted by the University of Illinois showed less injury from a 100-N-pounds-per-acre rate vs. 200-N-pounds-per-acre rate at various anhydrous application depths. Splitting N application timings between preplant and sidedress is one way to lower anhydrous rates applied before planting. 

Spring Application Guidelines

  • Don’t plant directly over ammonia injection tracks. Use GPS guidance to offset planter rows or apply at an angle to future corn rows.
  • Inject anhydrous at a depth greater than 6 inches and make sure the knife slot is sealing properly.
  • Lower preplant N rates by planning a postemergence sidedress application.
  • Don’t apply in wet soils. This can ensure the knife slot closes and doesn’t smear. 
  • Wait as long as possible before planting to allow for ammonia conversion to a safer form.
  • Consider switching to an alternate source of N, such as UAN solutions or urea.
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