Can dry soils affect anhydrous ammonia applications in Kansas?
Many producers are already starting with anhydrous application for summer crops this spring, however dry soils can be a concern. When the soil is dry, will it be able to hold anhydrous ammonia or will some or most of the ammonia be lost shortly after application?
There are three factors that come into play:
Chemical - Ammonia (NH3) needs to react with water shortly after application in order to
convert into ammonium (NH4+), which is the molecule that can adhere to clay and organic matter in the soil. Ammonia is very soluble in water. After it is placed in the soil, NH3 reacts with water in the soil to form ammonium-N (NH4+), which is retained on the soil cation exchange capacity sites. This process takes a little time – it does not occur immediately upon contact with the soil. The main controlling factors in the conversion of NH3 to ammonium-N are soil temperature, soil moisture, and soil pH. The higher the soil temperature and the wetter the soil, the more rapid the conversion occurs. If the ammonia does not react with water, it will remain as a gas that could escape from the soil. Also, equilibrium between NH3 and NH4+ is affected by soil pH. More NH3 will remain unconverted in the soil longer at higher application rates and at higher soil pH levels.
Physical - Dry soils may be cloddy, with large air spaces where the soil has cracked. This can allow the gas to physically escape into the air before it has a chance to be converted into ammonium. Getting the soil sealed properly above the injection slot can also be a problem in dry soils.
Application depth - The deeper the ammonia is applied, the more likely the ammonia will have moisture to react with, and the easier the sealing.
So, can anhydrous ammonia be applied to dry soils?
The answer is yes - as long as the ammonia is applied deep enough to get it in some moisture and the soil is well sealed above the injection slot. If the soil is dry and cloddy, there may be considerable losses of ammonia within just a few days of application if the soil is not well sealed above the injection slot and/or the injection point is too shallow.
Producers should be able to tell if anhydrous is escaping from the soil during application or if the ammonia isn’t being applied deeply enough. If ammonia can be smelled, the producer should either change the equipment setup to get better sealing or deeper injection, or wait until the soil has better moisture conditions. It is important to keep in mind that despite the current drought in Kansas, moisture can still be found at 6 inch depth in most soils/regions.
In short, producers can minimize this potential loss problem by:
- Applying the anhydrous ammonia at the proper depth (at least 6 to 8 inches in 30 to 40 inch spacings).
- Using covering disks behind the knives or sealing wings ("beaver tails") on the knives.
- Apply the anhydrous ammonia at least 1 to 2 weeks before planting. This waiting period should be even longer if soils are dry.
Dorivar Ruiz Diaz, Nutrient Management Specialist