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If you apply enough nitrogen early and don’t lose it during spring, you won’t likely need more.
Just add water
Cornfields typically need late-season N applications only if soils lost their N earlier in the season, due to excessively wet conditions or if the field didn’t receive enough N early on, Scharf says. “There is nothing wrong with an early N application that can supply the crop’s needs all the way through the season,” he says. “The only problem with that approach is if you lose N after it’s applied and you don’t get back in the field later on to apply more.”
When relying solely on spring preplant or sidedress anhydrous applications, farmers may be unable to complete operations on all their acres, if conditions are wet. “Sometimes it can be mid-June to early July before the ground dries up enough to get in the fields, and by then the corn might be too tall to do so,” Mitchell says. “That’s where a high-clearance sprayer is a really good risk-management tool to be able to apply N when it’s a challenge to put it on by any other means.”
Having the high-clearance sprayer gives his family’s operation “a third backstop for putting on N during the season,” Mitchell says. “We always have a window, sometime between the V6 to tasseling growth stage, when ground conditions are dry enough to allow us to make these high-clearance N applications. We also try to time our applications to when we know rain is coming so that the N is made available to the roots.”
The biggest concern in a rain-fed system, which includes most of the Midwest, is not having enough moisture after a supplemental application to move the N into the root zone, says Fabian Fernandez, University of Illinois Extension soil fertility specialist. “A half-inch of rain or more is typically needed to do this,” he says.
For late-season applications, the supplemental N also needs to be in a readily available form, such as urea or UAN, Fernandez adds. “Either liquid or granular N is fine, as long as it’s not in a slow-release form,” he says. “Irrigation can also make a huge difference in the success of late-season supplemental N applications, because with irrigation, farmers can make sure to move the N into the root zone, where plants can use it.”
Still, sometimes the soil will contain enough moisture that only minimal rainfall is needed to move N into the root zone, Scharf says. “If you throw a handful of dry N on the ground and it disappears overnight, that shows there is enough moisture in the soil to dissolve the product and wick it into the soil,” he says.