How Much Nitrogen is Left in Your Corn's Tank?

Wet spring zapped sizable percentage of N already applied.

Published on: Jul 18, 2011

Will your corn have enough nitrogen to finish its drive toward maturity? Or will it run out of gas due to an empty tank in the soil where N should be before it reaches its destination? That question is a pertinent one after a wet spring, yet a hard one to answer until deficiencies start showing up.

In some parts of the country specialists say spoil tests for N are reliable. In other parts, particularly from Indiana eastward, specialists contend there is too much rainfall to make those indicators good predictors of how much N a crop may still have left to produce corn upon.

"In fields where N was applied last fall, where that practice is still followed, even with an N inhibitor involved, there had to be N losses," says Barry Fisher, agronomist for the Natural Resources Conservation Service in Indiana.

Rainfall was especially heavy in Indiana and the eastern half of the Corn Belt this spring, particularly in April. "It was the wettest April for many people since 1895," he says. "So even if you put N out in the window of late March, some of it is gone. If you used an inhibitor, it might have helped, but a big amount is already lost."

Fisher prefers putting on most of the nitrogen on closer to when it will be needed. That means sidedress applications in most cases, although those proved problematic for some people with all the rain that allowed corn to continue growing and getting borderline on being too tall for ground equipment.

If you used an N inhibitor this spring, it probably would have helped cut down on losses. What the corn needs is the biggest possible dose of N when it reaches the grand growth phase, a bit later this year, but often around July 4.

Cover crops helped capture N left by last year's crop, but they immobilize the N temporarily. That's why no-tillers with similar approaches have agreed to apply N early as starter. In the early days of no-till, Fisher says. "That's why some people really suffered in their first few years trying no-till," he observes. "They didn't understand that while they could take credit for N captured by a cover crop, they couldn't just let corn go without N for that long of a period of time.