Corn Illustrated Weekly: Nitrogen Rate Differences Show Visually in Rate Plot

Study field needs good rain for full N effect to kick in.

One of the two major studies at Farm Progress Corn Illustrated plots this year tests how much nitrogen is the right rate. The study is replicated two times, but organizers know that it's still only answering the question, "What was the right rate for this location for this year?"

That's why Bob Nielsen and Jim Camberato, Purdue University agronomists, began collecting data on more than 30 nitrogen trials a year ago, scattered across Indiana. Their efforts continue this year with similar plots. Many of them, like the Corn Illustrated plot, are in real farm, real-field conditions, not just a university test. The goal is to gain enough data over enough environments to be able to draw conclusions about how much N it takes per bushel of corn, under varying conditions.

Both Iowa State University and Ohio State University have Web-based N-rate calculators that can help you determine how much N to apply in your area, on your soils, with your rotation. But both systems rely on a bank of data collected over the years. That's what's been missing in Indiana. Their goal is to have a data bank so Indiana farmers can take advantage of the same type of information many of you can already use.

What's different in the Corn Illustrated sidedress N rate test on the Jim Facemire farm, Edinburgh, Ind., is that it includes both zero and 50 pound rates. Many farmers who do farm N-rate trials are reluctant to include a zero rate, knowing it will be a big hit on yield.

A similar test in a different study sponsored by Stewart Seeds a year ago showed that the hit, while significant, may not be quite as large as one might think, notes Dave Nanda, a long-time plant breeder who assists with the Corn Illustrated plots. "We saw yields pushing 120 bushels per acre for zero sidedress rates, with an average just under 100 bushels per acre," he says. However, 20 pounds of starter N went down early, making the effective N rate 20 pounds per acre.

This year, 20 pounds of N per acre also went down as starter. So even the zero sidedress rate really received about 20 pounds N per acre in the plot. "What we missed last year was not having a rate between zero and 100 pounds of N per acre, sidedress," Nanda says. "Last year in this area, we didn't see any yield advantage above 100 pounds sidedress, or 120 pounds of total N per acre. It was following soybeans, so you also need to add N credit from the soybeans. This year's plot also follows soybeans.

"We were left wondering what would have happened if we had applied less than 100 pounds sidedress. That's why we included a 50 pound rate this year, Nanda says.
Even without rain after liquid N was applied June 4, Nanda seemed to be getting part of his answer already. "The one thing we picked up first visually so far was that you can pick out the zero sidedress plots, even from the 50 pound sidedress rate," Nanda says.

The plan is to carry the study to yield. Look for updates on the Corn Illustrated plots weekly.

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