The recommendations for Ohio, Indiana and Michigan focus on fertilizer and crop prices, rather than on yield potential. The new application rates and a nitrogen rate calculator are available online.

“It is intuitive that higher corn yields will result in greater nitrogen demand from the soil, but does that translate into higher nitrogen demand?” asked Robert Mullen, an Ohio State University soil scientist.

“Investigation of nitrogen rate studies conducted over several years reveals that there is not a strong relationship between maximum yield potential and the amount of nitrogen needed to achieve maximum yield. So utilizing yield potential to dictate nitrogen recommendations may not be the most effective method, especially when nitrogen costs are high. Historically, we’ve treated excess nitrogen as cheap crop insurance. While it was then, that’s not the case anymore.”

Fertility specialists throughout the Corn Belt have devised a new system that bases optimum nitrogen rates on the current price of fertilizer and the average price of the crop. For example, if nitrogen is 25 cents per pound and the price of corn is $2.50 a bushel, to achieve 175 bushels per acre of corn in northwest Ohio, the best nitrogen rate would be 156 pounds, with an application range of 150-180 pounds. As the cost of nitrogen or the price of corn changes, the optimum rate of nitrogen also changes.

In the past, growers would apply the maximum of 196 pounds of nitrogen to achieve 175 bushels per acre. This amount ensured that the crop suffered no nitrogen deficiency.

“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. If farmers are risk averse, they can use the high side of the rate range. If they are more willing to accept risk, they can use a lower side of the rate range, increasing their potential for economic reward.”

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 nitrogen. We know that’s not true,” Mullen said. “And the problem we run into is that we don’t know exactly how much nitrogen is in the soil and how much will be available to the crop. The release of nitrogen is dependent on the weather, so there’s always a possibility of adding more or less nitrogen to the soil than is needed.”

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

“Is it always economical to shoot for maximum yield? Research has shown that it’s not,” Mullen said. “It may take the same amount of nitrogen to reach 179 bushels per acre as it does to only reach 170 bushels per acre. It’s impossible to determine at what point the nitrogen level is reached to where it is no longer a benefit to gain more yield without a nitrogen rate trial in every field.”

Mullen has been educating Ohio farmers on the new nitrogen recommendations for several months, and the changes have been well received.

“Farmers may not yet be 100 percent comfortable with the changes, but they understand why it’s being done and can see the value in it,” Mullen said. “All land-grant universities in the North Central region are moving toward a similar basis for generating nitrogen recommendations.”

To check nitrogen recommendations for other states »

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