Researchers Find Value in In-season N
Recent studies show corn plants take up and use a large amount of nitrogen (N) during the growing season. Making sure the plant has access to nitrogen as it approaches flowering can improve yields. In-season N applications help ensure the plant has adequate N to fuel kernel development.
Researchers are reporting the value of in-season N 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 N is paying off best during wet years. Growers who apply N 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 N," 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 N application pose periodic risks.
"Logistically and financially, fall N application appears to have a place," Ferguson says. "However, it's not environmentally viable. Growers who apply N during the growing season reduce environmental risks and often save money."
Equipment Allows In-Season Application
Equipment is key to applying N during the growing season, Scharf says. "The emergence of high-clearance spinners is helping," he reports. "It's a fast way to apply nitrogen to a lot of acres."
Sprayers also allow in-season application with a wider window of opportunity to get into the field. However, growers can't cover as many acres as quickly, making sprayers more dependent on good weather.
While Ferguson sees value in nitrogen inhibitors (which allow slower release of N), he's urging growers to adopt sensor-based in-season N applications. One drawback is that plants need to reach the V8 stage before sensors are effective. Growers using toolbars usually can't wait this long. If a grower has high-clearance equipment, Ferguson suggests applying from V8 to V14.
Fertigation Offers Wide Application Window
On irrigated acres, fertigation allows a wide window for N application. Nitrogen uptake efficiency can reach 90% with fertigation, well above the 50% we often see with soil-applied N.
For growers who adopt in-season N application, the question becomes how much preplant N 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 N 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 to 50 lb/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."
Corn N Needs Increase
Higher-yielding modern hybrids require more N and are taking it up from the soil later in the growing season. As yields go up, late-season N needs will go up as well.
"We're seeing hybrids take up more N 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 N application."
"The key is getting enough N into the soil when the crop needs it," Scharf says. "The best way to do this is to apply N 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 N during reproduction and grain fill can boosts yields, save money and lessen environmental concerns that come with earlier N application strategies.
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