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Corn+Soybean Digest

At Any Rate, Nitrogen Applications Getting Pricey

Nitrogen (N) application recommendations for Midwest farmers will soon be changing, mainly driven by a need to be more cost efficient as fertilizer prices continue to rise.

Historically, fertilizer recommendations for Ohio, Indiana and Michigan field crops have offered optimum N rates based on the maximum yield potential for a particular area.

Such a system, however, relies on N being inexpensive and over-application not too costly, said Robert Mullen, an Ohio State University soil scientist. Both are no longer the case.

"This approach has served agriculture well. The economic detriment due to over-application has historically been small from an economic standpoint," Mullen said. "But as nitrogen prices have risen over the past several years, the economic penalty for over-application has reached a point where economic considerations need to be made.”

Fertility specialists throughout the Corn Belt have devised a new system basing optimum N rates on the current price of fertilizer and the average price of the crop. For example, if N is 25¢/lb. and the price of corn is $2.50/bu., to achieve 175 bu./acre of corn in northwest Ohio the best nitrogen rate would be 156 lbs., at an application range of 150-180 lbs. As the cost of N or the price of corn changes, the optimum rate of N also changes.

"It boils down to an exercise in risk management," Mullen said. "The old system uses a single value, while this new system gives farmers a range to work with.”

Current fertilizer recommendations needed to be updated for several reasons, Mullen said.

“One reason is that the system assumes the soil is a blank medium and devoid of natural N. We know that's not true," he said. "And the problem we run into is that we don't know exactly how much N is in the soil and how much will be available to the crop.”

Also, N applied to the soil always reaches a point of saturation, and yield eventually levels off no matter how much more N is added, Mullen said. As a result, farmers could be wasting money on unneeded N using current recommendations.

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