Value of in-season nitrogen application

Corn plants take up and use a large amount of nitrogen during the growing season. Making sure the plant has access to nitrogen as it approaches flowering can improve yields. In-season nitrogen applications help ensure the plant has adequate nitrogen to fuel kernel development.

Researchers are reporting the value of in-season nitrogen applications and suggesting growers can gain real economic and environmental benefits by adopting this practice.

Peter Scharf, professor of plant sciences at the University of Missouri, notes in-season nitrogen is paying off best during wet years. Growers who apply nitrogen in the fall or early spring may lose a substantial amount to runoff and leaching during wet springs.

"When you have a wet spring, you can lose a lot of nitrogen," Scharf says. "This happens in a lot of states on a lot of different soils."

Richard Ferguson, professor of soil science at the University of Nebraska, says growers should try to avoid putting down fertilizer that's likely to be lost. Since we can't predict winter or spring rainfall, fall and early-spring nitrogen application pose periodic risks.

"Logistically and financially, fall nitrogen application appears to have a place," Ferguson says. "However, it's not environmentally viable. Growers who apply nitrogen during the growing season reduce environmental risks and often save money."

Corn nitrogen needs increase

Higher-yielding modern hybrids require more nitrogen and are taking it up from the soil later in the growing season. As yields go up, late-season nitrogen needs will go up, as well.

"We're seeing hybrids take up more nitrogen later in the growing season," Ferguson says. "Half or less of the plant's needs is taken up before tasseling. There seems to be a lot to gain and little to risk with in-season nitrogen application."

"The key is getting enough nitrogen into the soil when the crop needs it," Scharf says. "The best way to do this is to apply nitrogen as close as possible to when the plant can take it up and use it."

Growers may need to change their mindset about getting into the field and supplying the growing crop. It requires the right equipment. However, the returns on that investment can be healthy. Feeding nitrogen during reproduction and grain fill can boosts yields, save money and lessen environmental concerns that come with earlier nitrogen application strategies.

Fertigation offers wide application window

On irrigated acres, fertigation allows a wide window for nitrogen application. Nitrogen uptake efficiency can reach 90% with fertigation, well above the 50% we often see with soil-applied nitrogen.

For growers who adopt in-season nitrogen application, the question becomes how much preplant nitrogen should they apply and how much should they deliver during the growing season. Scharf notes that growers in the Corn Belt tend to apply two-thirds of nitrogen needs before planting and the other third during the growing season. He suggests the ratio should be reversed if growers can adapt fertigation.

"I'm more comfortable with 30-50 lbs./acre preplanting," he says. "Growers could put nothing down before planting if they can get into the field to apply when the crop is knee high."

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