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Where you farm impacts how much N you need

LOCATION, LOCATION, LOCATION: Where this field is located indicates more than soil type and climate. It also influences the economic optimum nitrogen rate for growing corn.
Twelve years of on-farm trials show optimum economic nitrogen rate varies by soil type.

One thing showed up quickly when Bob Nielsen and Jim Camberato began conducting nitrogen rate trials on farms across Indiana a dozen years ago. They discovered that farmers in some parts of the state can apply considerably less nitrogen than others and still get maximum economic return.

Nielsen is the Purdue University Extension corn specialist. Camberato is an Extension soil fertility specialist. They set out to compile data so they would have a modern benchmark for making recommendations. They weren’t sure what they would find when they began the project.

“The large difference in the amount of nitrogen it takes in some parts of the state may be surprising,” Nielsen says. “We’ve seen enough consistency in results across enough farms to feel confident in saying that if you farm in certain locations, you’re going to need to apply more nitrogen than if you farm in other areas.”

While they suspect that soil type is the major factor, there could be other factors, as well, Nielsen notes. Climate also varies within the state.

Big differences
As the tables below indicate, the difference in recommended nitrogen rate can be sizable depending on where you are in the state. These tables represent recommendations to reach the economic maximum yield potential at varying corn and nitrogen prices. Economic optimum is the point at which you would net the most return per acre. It’s not necessarily the rate that would produce the highest yield.


For example, suppose corn is $3.50 per bushel and nitrogen is 40 cents per actual unit of N. In northeast Indiana, you don’t reach economic optimum until you apply 223 pounds per acre, based on past results. In east-central Indiana, you would need 220 pounds per acre.

But in west-central and southern Indiana, you could reach optimum by applying 177 pounds per acre, on average. That’s more than 40 pounds less than if you live in east-central or northeast Indiana. You would spend between $16 and $18 less per acre to buy N.

Check out tables for other parts of the state.

TAGS: Fertilizer
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