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Need help deciding how much N to apply?

wet cornfield
RETHINK N RATE: You can follow Purdue recommendations for your location unless you apply nitrogen very early before planting, or it’s very wet early in the growing season.
There are several aids available to help determine the best nitrogen rate to use. Here’s a look at two.

You can learn about products to aid nitrogen application in corn on the web. Visit for a rundown on products and trials. Make your own decision on which of these products or methods you want to investigate further.

Nitrogen computer models are offered for helping fine-tune N rates. Adapt-N is a computer model developed at Cornell University and available commercially through Agronomic Technology Corp. Some universities in the Midwest have used Adapt-N in the past with varying results.

Encirca from DuPont Pioneer and programs offered by The Climate Corporation also have nitrogen predictive components. This is not an all-inclusive list.

Another option is to rely on recommendations from universities based on trials. Bob Nielsen is the Purdue University Extension corn specialist and Jim Camberato is the Extension soil fertility specialist at Purdue. They’ve conducted nitrogen rate trials on farms in Indiana for 12 years.

“The data we’ve developed is a good guide if you’re seeking nitrogen rates to achieve economic optimum yields,” Nielsen says. “They should be accurate as long as you don’t apply nitrogen a very long time ahead of when the plant will use N. The farther ahead you apply, the greater the chances for N losses.”

ISU calculator
Nielsen and Camberato’s data was used to determine calculations included in the Iowa State University Nitrogen Rate Calculator for Indiana. Until Nielsen and Camberato began doing modern research, there wasn’t a lot of data backing up Indiana’s numbers.

Find the calculator online. It uses a few different terms, including marginal return to nitrogen (MRTN). That equates to optimum economic return — the phrase used by Nielsen and Camberato. It’s the rate at which you expect to capture the most net return for dollars invested in nitrogen.

To use the ISU calculator, simply select Indiana, then your crop reporting district. As Nielsen and Camberato discovered, location within the state makes a big difference in recommended rates.

The display includes a graph; the optimum economic rate, marked as MRTN; and a range of rates that should produce similar results.

Purdue recommendations
Nielsen says you can also visit the Purdue nitrogen recommendations and management guidelines on the website he manages. You’ll find the same information used to produce results in the ISU calculator. The only difference is that the results are in table form.

There are several tables for various crop reporting districts with varying nitrogen recommendations, based on results of on-farm trials.  

The table for the northwest and north-central crop reporting districts in Indiana is shown below. If recommendations are nearly the same, crop districts are combined into one table.



If you live in Morocco, Ind., for example, you would use this chart. If corn is $3.50 per bushel and nitrogen is 40 cents per pound, the recommended economic optimum rate is 183 pounds per acre. The ISU calculator also recommends 183 pounds per acre.

If you want to use the Purdue recommendations directly, view these charts for other locations.


TAGS: Fertilizer
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