Is the soil too dry to apply anhydrous ammonia?

Dry soils are a challenge to in-soil banded nitrogen application, especially anhydrous ammonia.  When anhydrous ammonia is injected into soil the ammonia (NH3) is dissolved in water and reacts to convert to ammonium (NH4+), which is positively charged and held by the cation exchange on the soil particles.

Soil moisture is needed to allow the ammonia to convert and be retained in the soil, however even in dry soils there is usually enough moisture present for this to occur.  The major problem with dry soils is the clods or lumps that form can prevent a good seal, allowing the ammonia to be lost through large voids between clods before dissolution in moisture occurs. Indeed, nitrogen losses on low moisture soils are caused more by poor physical soil structure (soil tilth) than by a lack of moisture to chemically react with ammonia.

Clay soils that are very dry will be cloddy or lumpy and may permit too much gaseous ammonia to escape. The zone of ammonia dissipation from the injection point is larger in dry soil, so although the soil may be difficult to work, deeper injection may actually be required.  Lighter textured soils will have better tilth than dry clay soils and will be more likely to produce a good seal to retain the ammonia.

Slot closure may be better on previously worked  than on uncultivated soils if the soil flows and seals better.  Such is not the case if soils were cloddy.  Some cereal crops were harvested almost 2 months ago and the moisture that has been received may be sufficient to provide good tilth.  Soil moisture and texture varies across the province, as does farm equipment.  The only way to assess your soil conditions is a test run with your applicator. An application pass without N will indicate whether soils are too cloddy and injection slot closure is inadequate. If after making a round with N, you can still smell ammonia from the previous application, make adjustments in depth or closure modifications.  Or wait for rainfall to improve soil structure.

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