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Corn+Soybean Digest

Wet-Spring Nitrogen Application Tips For Corn

Corn growers can choose from many alternatives when it comes to applying nitrogen (N) this spring. They just need to make sure to have the right equipment and fertilizer products on hand to get the job done, says Peter Scharf, University of Missouri Extension nutrient management specialist.

With flooding already a reality in many parts of the Corn Belt and EL Niño weather patterns threatening to bring more moisture than normal into the region, farmers may have to change longstanding practices in order to apply N in both a timely and efficient manner. “A lot of people feel that they have to apply N before they plant, but our research suggests that you really have a fairly big window of opportunity after planting to apply N before a delay will hurt yields,” says Scharf. “In a year when your opportunities to operate machinery in the field could be very limited, it might be a mistake to spend time applying N when the conditions are right for planting.”

N applications can wait until after planting if you don’t have time to do both in the timeframe needed to plant corn for optimal yields, he explains. “Sometimes, it’s even a benefit to wait to apply N,” says Scharf. “Last year, for example, we saw as much as a 70-bu. yield advantage from applying N knee-high vs. applying it preplant.”

In the northern Corn Belt, however, delaying N application too late into the growing season can limit yield potential says John Sawyer, Iowa State University Extension soil fertility specialist. “If sidedressing is planned, and especially if that application will be made late, then having a split N application of around 20% preplant or at planting will carry the corn until sidedress N is applied,” he says. “This is especially important for corn following corn.”

If soil conditions are wet, farmers who are equipped to sidedress N will likely be the most efficient users of N fertilizers, adds Sawyer. “In a wet spring or a wet early summer, sidedressed N should perform better than N applied preplant, because there is typically less N-loss associated with sidedressing,” he says. “In contrast, preplant N applications typically work better when conditions are dryer-than-normal during spring and early summer or equally as well with sidedress when conditions are normal.”

Soil type and soil drainage can also make a difference, adds Sawyer. “Sidedressing is typically better for poorly drained soils or sandy, or excessively drained soils, where there’s more risk of N loss,” he says. “For moderate to well-drained, fine-textured soils, that don’t tend to pond, the N-loss risk is lower, and preplant N applications can perform equal to or better than sidedressed applications.”

Still, a second advantage to having sidedress equipment is the option to apply rescue N treatments later in the season, if needed, says Sawyer. However, farmers don’t necessarily need sidedress equipment to make profitable N-rescue applications, points out Scharf.

“There are lots of ways to apply N after planting,” says Scharf. “Sometimes producers may have to hire it done and sometimes they can use equipment that they already have.”

For example, many farmers already have a sprayer that they can set up with drop nozzles on 30-in. centers to apply liquid N, notes Scharf. “They may need to refill their tanks a lot, which wouldn’t be anyone’s first choice,” he says. “Yet, having a sprayer set up to apply N gives corn growers a wider application window if they do decide to plant first and apply N later.”

Farmers who prefer not to invest the time and money into sidedress or drop-nozzle application systems could choose other N-application methods that may be faster, in some cases, but also come with other problems to watch out for, says Scharf. “For example, broadcasting dry urea is a very fast way to apply N, but poor fertilizer quality can cause spreading problems,” he says. “Imported urea goes through a lot more augers than domestic urea, which breaks down the particles so that you can’t throw them well with a spinner.

“If you know you have a good-quality dry N product, then I’d say go ahead and plant first and apply N later,” he adds. “However, broadcasting N won’t do you any good if it’s poor quality and results in streaking. I wouldn’t ever buy dry N sight unseen. Go look at it first and make sure it’s not full of powder so you can spread it evenly.”

Another possible option is use an air-boom truck to broadcast it, adds Scharf. “This will work much better than a spinner spreader on poor-quality urea,” he says. Farmers can also treat dry urea with a urease inhibitior to help slow volatile N loss if surface broadcasting, says Sawyer.

Whatever N fertilizer product farmers decide to apply this spring, there should be few difficulties obtaining what they need, says Sebastian Braum, a Yara North America agronomist. “The supply of fertilizer is not going to be much of a problem this year,” he says. “Everything should be readily available and prices should be more affordable than they have been the last couple years.”

From an efficiency perspective, however, Braum says farmers who are able to sidedress 32% urea-ammonium nitrate (UAN) solution will likely garner the best value for their dollar. “Sidedressing 32% UAN is a good hedge against N loss, especially if you anticipate a cool, wet spring,” he says. “Good managers know that they’ll get the best performance out of their N dollars if they split-apply. So, I would recommend putting half your N down pre-plant as close to planting as possible and half your N down after planting.”

Sidedressing anhydrous ammonia works too, Braum says. However, “you need to really stay within the rows or you’ll burn the roots, and it takes longer for the N to become available to the corn than 32% UAN, which becomes available to the crop immediately,” he says.

Some people do plant corn without applying any N, Braum adds, “but that can be a risky strategy if the weather turns too wet to sidedress and they don’t have any other way to apply it.”

For more recommendations on spring fertilizer application strategies for corn, click here:, or here:

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