Posted 5 June 2009. Crop Management.
Nitrogen Losses No More Than Normal, Despite Wet Spring
Purdue University. www.ag.purdue.edu
West Lafayette, Indiana (May 28, 2009)--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, said a Purdue University expert.
Nitrogen losses should be about average because of the cooler-than-normal temperatures across the state, said Jim 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 percent of the nitrogen if they did not use a nitrification inhibitor such as N-Serve," Camberato said. "Fortunately, most Indiana farmers apply their anhydrous in the fall with a nitrification inhibitor, and we estimate the average loss to be about 15 percent of the applied nitrogen."
A nitrification inhibitor slows the conversion of nitrogen to nitrate -- the form that is lost.
"For anhydrous applied in the spring without a nitrification inhibitor, we also estimate 15 percent of the nitrogen to be lost," he said. "If a nitrification inhibitor is used with spring anhydrous, dependent on when it was put out, losses will be minimal."
Camberato said farmers who planted shortly after anhydrous application should watch for anhydrous injury, particularly in sandy soils.
The best application of nitrogen 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 said. If itís injected at least 2 inches deep, ammonia loss is eliminated. When dribbled on the soil surface, losses of UAN are only about 5 percent of the nitrogen 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 percent of the nitrogen content as ammonia to the air, so I do not recommend them," Camberato said. "If you want to leave urea on the surface, then adding a urease inhibitor, such as Agrotain to the urea should be considered."
However, he said making an injected application of UAN would still be better than adding the inhibitor to urea.
Because nitrogen is relatively expensive compared to grain lately, one should consider the cost of nitrogen and the value of the grain for determining the rate of sidedress nitrogen application, Camberato explained. A Corn Nitrogen Rate Calculator based on recent Purdue research by Camberato and Bob Nielsen, Purdue Extension corn management specialist, is available at extension.agron.iastate.edu. The calculator is designed to help farmers calculate the economic return to nitrogen with different nitrogen prices and corn prices. For more information on modifying recommendations derived from the calculator, visit www.agry.purdue.edu.