Even though it’s been an unusually wet spring in Indiana, it was cold enough to limit the conversion of anhydrous ammonia to nitrate during the rainy periods, says Jim Camberato, a Purdue University expert.
Nitrogen (N) losses should be about average because of the cooler-than-normal temperatures across the state, says Camberato, Purdue Extension soil fertility and plant nutrition specialist.
“If a farmer applied anhydrous in the fall, the average loss would be estimated at about 30% of the N if they did not use a nitrification inhibitor such as N-Serve,” Camberato says. “Fortunately, most Indiana farmers apply their anhydrous in the fall with a nitrification inhibitor, and we estimate the average loss to be about 15% of the applied N.”
A nitrification inhibitor slows the conversion of N to nitrate – the form that is lost.
“For anhydrous applied in the spring without a nitrification inhibitor, we also estimate 15% of the N to be lost,” he says. “If a nitrification inhibitor is used with spring anhydrous, dependent on when it was put out, losses will be minimal.”
Camberato says farmers who planted shortly after anhydrous application should watch for anhydrous injury, particularly in sandy soils.
The best application of N is to sidedress UAN  (urea ammonium nitrate) or anhydrous UAN by either injecting it into the soil or dribbling it onto the soil surface, he says. If it’s injected at least 2 in. deep, ammonia loss is eliminated. When dribbled on the soil surface, losses of UAN are only about 5% of the N applied.
“A broadcast application of UAN between the corn rows or a broadcast application of urea left on the soil surface have the potential to lose 15% or 30% of the N content as ammonia to the air, so I do not recommend them,” Camberato says. “If you want to leave urea on the surface, then adding a urease inhibitor to the urea should be considered.”
However, he says making an injected application of UAN would still be better than adding the inhibitor to urea.
Because N is relatively expensive compared to grain lately, one should consider the cost of N and the value of the grain for determining the rate of sidedress N application, Camberato explains. A corn N rate calculator  based on recent Purdue research by Camberato and Bob Nielsen, Purdue Extension corn management specialist, is available online. The calculator is designed to help farmers calculate the economic return to nitrogen with different nitrogen prices and corn prices. More information  on modifying recommendations derived from the calculator.