Why wait?
by John Sawyer and Elwynn Taylor, Department of Agronomy

If you are considering applying anhydrous ammonia or manure with a high ammonium N content this fall, remember to wait until temperatures cool to 50 °F and will continue to get colder.

Why is this important? The form of nitrogen that can potentially be lost from soils due to wet conditions is nitrate (NO3—) (Figure 1). The form applied as anhydrous ammonia is NH3, which is quickly converted to ammonium (NH4+) when it comes in contact with water in soil. Ammonium can also be already present at high levels in some manure sources, such as liquid swine manure. Because ammonium is a positively charged ion, it is attracted by electrostatic forces to negatively charged soil. Ammonium is not leached or lost by denitrification (conversion to nitrogen gas). Therefore, it will stay in soil even if the soil becomes excessively wet. Nitrate, which is produced by soil microbes from ammonium in a process called nitrification, is a negatively charged ion and is leachable and subject to denitrification.

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