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College of Food, Agricultural, and Environmental Sciences


Growers to See Changes in Nitrogen Application Recommendations

October 13, 2005

WOOSTER, Ohio — Nitrogen 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, tri-state (Michigan, Ohio, Indiana) fertilizer recommendations for field crops have offered optimum nitrogen rates based on the maximum yield potential for a particular area. For example, to achieve an average yield of 175 bushels per acre of corn in northwest Ohio, farmers should apply 196 pounds of nitrogen. This amount ensures the crop suffers no nitrogen deficiency.

Such a system, however, relies on the fact that nitrogen is inexpensive and over-application is not too costly, said Robert Mullen, an Ohio State University soil scientist with the Ohio Agricultural Research and Development Center. 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," said Mullen. "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. Producers, especially those managing large acreages, are beginning to look at fertilizer nitrogen application from an economic standpoint."

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. So, 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 to 180 pounds. As the cost of nitrogen or the price of corn changes, the optimum rate of nitrogen also changes.

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

Mullen said that the current fertilizer recommendations needed to be updated for several reasons.

"One reason is that the system assumes the soil is a blank medium and devoid of natural nitrogen. We know that's not true," said Mullen. "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."

Another point Mullen made is that 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," said Mullen. "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."

The new nitrogen application recommendations will be the focus of Mullen's extension presentations during producer and consultant meetings and field days this fall and winter. Ohio State University Extension fact sheets and bulletins will highlight changes to the current tri-state recommendations beginning this winter.

Candace Pollock
Robert Mullen