Up to one-fourth of Indiana’s N goes on in the fall as anhydrous ammonia, almost all of it with an inhibitor, estimates Purdue’s Jim Camberato, fertility specialist.

“The earlier you apply, the more efficient anhydrous ammonia is compared to other forms, because it is the slowest form to convert to nitrate,” he adds. “So that’s the form to use in the fall or with early spring applications, especially in a wet spring or fall. But we can lose 15% of that to the environment, even with an inhibitor, research shows. So the less N you apply in the fall, the better. We get a lot more rain in the fall and winter, so you see a lot more sidedressing here—I would say at least 50% of the corn is sidedressed in our area and maybe more in Ohio.”

Over time, there’s little difference in using liquid N and anhydrous ammonia at sidedress, Camberato says. “Because sidedressing is a later application and the soil is drier at that time, you don’t get much loss with either form. But in a wet year, you could lose more with liquid N because about one-fourth of it is in nitrate form and is susceptible to loss immediately. It’s an even bigger issue with preplant because the time is longer before plant uptake.”

Banding urea instead of broadcasting either the granular or liquid form will slow conversion to nitrate.

In Ohio, UAN is the predominant form of N used, “partly because of safety issues,” says Extension Agronomy Field Specialist Greg LaBarge of Marion, Ohio, “and partly because that’s the form providers handle.” There was no corn yield difference between UAN and ammonia in a six-year study that he and OSU Fertility Specialist Robert Mullen conducted from 1998 to 2004.

observed average nitrogen rates