It is almost time that anhydrous ammonia (NH3) applications could begin (remember 50° F and cooling 4-in. soil temperature). However, many soils in Iowa are quite dry this fall. So, can anhydrous ammonia be applied to dry soil? Will it be held in dry soil?

Can anhydrous ammonia be applied to dry soils?

Yes. Dry soil can hold ammonia. Even airdried 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. Wing sealers immediately above the outlet port on the knife can help close the knife track, limit the size of the retention zone and reduce vertical movement of ammonia. Closing disks can reduce ammonia loss by covering up the injection track with soil that traps the ammonia as it moves to the soil surface. Reducing the application rate or narrowing the knife spacing reduces the concentration of ammonia in each injection band. If soils are dry and in good physical condition, they hold more ammonia than soil that is moist.