As producers start thinking about anhydrous application for wheat this fall, extremely dry soils can be a concern, said Dave Mengel, K-State Research and Extension soil fertility specialist. The question often is, when the soil is dry, will it hold anhydrous ammonia or will some or most of the ammonia be lost shortly after application?
Three factors help determine whether ammonia might be lost after application under dry conditions, Mengel said.
The first is how quickly the ammonia gas is converted within the soil to a non-gaseous form that will stay in the soil.
“Ammonia gas needs to react with water shortly after application in order to convert into ammonium, which is the molecule that can attach to clay and organic matter in the soil,” Mengel said.
Converting from gaseous ammonia to the less-volatile ammonium ion takes a little time – it does not occur immediately upon contact with the soil, he explained.
“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, a higher percentage of the ammonia will remain unconverted in the soil longer at higher application rates and at higher soil pH levels,” he said.
The second factor to consider is how rough and open the dry soil is, Mengel said.
“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,” the agronomist said. “Getting the soil sealed properly above the injection slot can also be a problem in dry soils.”
The third factor is the amount of ammonia that might be lost, which depends on application depth, he said. 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?
“Yes,” the soil fertility specialist said, “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 ot well sealed above the injection slot 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, he said.
Mengel said producers can minimize loss of ammonia when applied to dry soils 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; and
* Applying the anhydrous ammonia at least one to two weeks before planting. This waiting period should be even longer if soils are very dry.