Yes, it is OK to apply NH3 in dry soils, say Iowa State University (ISU) agronomists, as long as you do not smell the ammonia in the field after making the application. The question has come up as some retail suppliers are offering farmers what appears to be attractive pricing on NH3 provided it is applied during the fall.
ISU's Dr. John Sawyer addressed the issue last fall in ISU's Integrated Crop Management News: "Yes. Dry soil can hold ammonia. Even air dried soil contains some moisture, although quite low. Ammonia dissolves readily in water, but it is held or retained in soil by clay and organic matter. The problem with dry soil and low moisture is that soil moisture is needed to temporarily hold ('go into solution') the ammonia so it can become attached to clay or organic matter as ammonium. If dry soils are cloddy and do not seal properly, the ammonia can be lost at injection, or seep through the large pores between clods after application. Therefore, proper depth of injection and good soil coverage are a must for application into dry soils."
Sawyer's cautioning comments: "Be mindful of what is happening at application, especially if soil conditions are not ideal. If you make an application round in the field, and you can still smell ammonia from that application, then you should make adjustments or wait for better conditions. If the soil is breaking into clods, there isn’t good coverage of the knife track with loose soil, and ammonia is escaping (remember your nose tells you if ammonia is escaping; a white vapor is condensed water vapor, not ammonia which is colorless), then stop and either change the way the equipment is working or is set up, or wait until the soil has better structure or moisture.