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Issue No. 4, Article 9/April 21, 2006

Use Caution When Preplanting Anhydrous Ammonia and/or Using Urea in Starter

(Originally published as an "Alert" on April 18)

While nitrogen fertilizers are very beneficial for crop production, if misapplied they can cause serious crop growth problems early in the season. To minimize the risk of such damage, keep anhydrous ammonia and urea-containing products away from the seed and rooting zone of small plants.

Do not use ammonia with spring strip-till. Doing so places the ammonia directly below the seed zone. If the soil cracks open along the ammonia knife track, the free ammonia will move up into the seed zone and inhibit germination and/or prune or kill roots. Yield loss of 50 to 60 bushels per acre has been observed from such damage. For those that have strip-tilled with ammonia in the spring without a problem, consider yourself lucky.

Suggestions to minimize seedling damage from spring preplant anhydrous ammonia follow:

  • Apply ammonia at an angle to the row.
  • Wait three to five days after ammonia application before planting. (This will not ensure that damage will not occur but gives some safety. Damage has been observed on seedlings when ammonia has been applied as much as two weeks prior to planting.)
  • Do not apply ammonia to soils that are wet. When ammonia is injected into wet soils, the soil along the knife track is compacted, resulting in trapping of the ammonia in a small zone. If soils dry and crack, the crack will occur along the knife track and allow the ammonia to move toward the soil surface.
  • If you are planning to till the field, apply the ammonia first and then field cultivate. The field cultivation will improve the soil seal of the ammonia by stirring loose soil into the top few inches of the knife track.

Do not allow urea-containing products (urea or UAN solutions) to come in contact with corn seed. Urea converts to ammonia when soil applied. If it is in contact with the seed, there may be enough ammonia produced to kill the seed. Even if it doesn't kill the seed, the free ammonia may inhibit phosphorus uptake. Most urea-containing products contain an impurity called biuret, a compound that is very toxic to seedlings.

There is no concern about the impact of urea-containing products on seed or seedlings if the products are broadcast and incorporated. The rate of urea that would get near the seed when it is broadcast is below the concentration necessary to cause seedling damage. If the urea-containing materials are applied with a starter attachment that ensures the fertilizer will be kept at least two inches from the seed, seedling damage is not of concern.--Robert Hoeft

Robert Hoeft

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