By DEBORAH BEHRENDS
Illinois Correspondent

URBANA, Ill. — Corn growers don’t need to worry about the cation exchange capacity (CEC) of the soil when determining how much anhydrous ammonia to apply, according to Fabian Fernandez, a University of Illinois extension specialist in soil fertility and plant nutrition.

CEC is a soil property important in determining liming application rates to correct acidity (pH) or to determine the capacity of a soil to supply plant nutrients. When anhydrous is applied, the ammonia reacts with organic matter and clay and, most importantly, it dissolves in water, Fernandez said.
“A false concept has been circulating this winter that anhydrous ammonia applications should not exceed 10 pounds of nitrogen per unit of CEC. This concept has no scientific foundation,” he said.

Because the word anhydrous means “no water,” when anhydrous ammonia is applied, it reacts with water to form ammonium.

“The initial reactions with water, organic matter and clays limit the mobility of ammonia and help retain nitrogen that could be lost by ammonia volatizing to the atmosphere. However, CEC does not have a direct relationship to how much ammonia a soil can hold at the time of application,” Fernandez said.
Other factors important in ammonia retention include soil texture, soil structure and method of application, including depth of injection and proper closure of the knife track. In some UoI trials, after ensuring adequate soil moisture conditions and proper application depth, researchers have successfully applied more than 200 pounds of nitrogen per acre in sandy-textured soils.

The question remains how much to apply and when to apply it. Fernandez said corn does not need a large amount early in the season. He recommends 30 pounds per acre or so to get the crop growing, until sidedress-nitrogen application time.

“While split applications do not save as much time as single applications, they are becoming more popular because they can reduce the risk of N loss should soil conditions become conducive to it,” he said.

“For those who applied N in the fall, so far this year, conditions have been favorable to preserve it, and I suspect that as long as fall applications were done as recommended, there is little need to worry about N loss at this point.”
A corn nitrogen rate calculator may be found online at extension.agron.iastate.edu/soilfertility/nrate.aspx

As for a good time to apply N, if needed, Fernandez said to keep in mind that the longer time lapsed between application and when the crop starts using N, the greater the potential for N loss. The bottom line? “You should not worry about the CEC of the soil in determining how much anhydrous ammonia to apply.”