Air Out Your Nitrogen Application Window

Sidedress urea with more confidence and precision using a pneumatic applicator.

By Jason Jenkins | Photos By Peter Scharf

It’s a sight corn producers dread: evenly spaced streaks of yellow running the length of their fields. If dry nitrogen was applied, it’s a telltale sign that the fertilizer spreader, the operator or both didn’t do their job very well.

“From georeferenced aerial photos, you can actually calculate the swath width and match it up to the kind of spreader that was used,” says Peter Scharf, a nutrient management specialist for University of Missouri Extension. While it can happen every year, “the uneven application really sticks out like a sore thumb in years when nitrogen loss has occurred” due to excessive rainfall, he says.

Producers have many variables to consider when planning their corn fertility program. Prescribing the “4Rs” of nutrient stewardship—putting the right source of fertilizer at the right rate at the right time in the right place—is a lot easier on paper sitting at the kitchen table in February than it is in practice once the season begins.

Confounding Factors

Because of its ability to be applied quickly, urea is a popular nitrogen source for topdressing. However, fertilizer quality, application equipment accuracy and weather conditions all play roles in determining whether the crop truly receives the fertilizer it needs when it needs it.

According to Scharf, uneven urea application is often the result of attempting to spread lower-quality fertilizer with a spinner spreader. As urea granules are handled, they tend to break into smaller pieces.

“So, the more it’s handled, the smaller and smaller it gets, and you can’t throw dust very far,” he says. “All those fines end up behind the spreader where the rate will be much higher than at the edge of the swath.”

In 2017, Matt Darr, professor of agricultural and biosystems engineering at Iowa State University, conducted urea fertilizer testing that assessed two types of application equipment—spinner spreaders and pneumatic boom applicators. He tested the equipment over bare ground, in corn at both the V10 and V15 stages, in high-wind conditions and with lower-quality urea.

“The spinner’s spread width was noticeably reduced by the poor urea, creating an inverted ‘V’ pattern with higher application directly behind the machine,” Darr says. “The pneumatic boom applied a more uniform rate.”

Scharf agrees with Darr’s findings. “You can’t throw dust, but you can certainly blow it,” he says. “If I had poor-quality urea, I’d feel a lot better with pneumatic boom than with a spinner.”

The Air Advantage

Such uniform application is exactly why AGCO® created the AirMax® as the dry fertilizer spreader of choice for its RoGator® by Challenger® series of high-clearance row-crop application equipment. Because metering is separate from distribution, the pneumatic system ensures that every plant gets the prescribed amount of nitrogen, without the need to adjust the machine with every load.

“That’s a definite advantage, allowing a producer to apply exactly the rate that the corn needs no matter the quality of the fertilizer,” says Mark Mohr, AGCO tactical marketing manager for application equipment. “Not only does that save on the bottom line, it also improves the success of a grower’s nutrient stewardship program.”

Apply Later If Needed

In his research, Scharf has found that while corn does have specific nitrogen requirements, the crop isn’t particularly sensitive to the timing of the application. The further a producer can push sidedressing into the season, the more accurate the nitrogen rate can be.

“Yes, the crop needs enough nitrogen, but the corn doesn’t really care very much when it gets applied in the vegetative stages,” he explains. “The later you can wait in the season, the more opportunity you have for diagnostics by looking at the color of the plants. If it’s been dry, you can flex your rate down. If it’s been wet, maybe you need to flex it up. Having a tall machine that can go out later gives you that ability.”

Darr’s study also revealed that while spinner spreaders provided reasonable results with corn at the V10 stage (waist high), they failed to deliver even marginal spread patterns at V15 (head high) due to the crop canopy height interfering with the discharge point on the spinner and shifting the application pattern. The pneumatic boom, however, was up to this challenge.

“The AirMax provided consistent fertilizer distribution up to V15 plant stage tested in our study,” he says. “The lack of a pattern shift supports late-season variable-rate application.”

Because urea is a fairly light material, windy conditions also can impact its application, even if it is high quality. Darr’s testing revealed that even in a 12-mph wind, the spinner spreader’s pattern shifted.

“The pneumatic boom had more consistent application, similar to low-wind conditions,” he says. “By minimizing the impact of wind, we maintained greater uniformity across the application zone.”

Darr says that while spinner spreaders may allow operators to sidedress waist-high corn faster, pneumatic boom applicators are superior in their consistency of distribution across the swath width.

“With the ability to deliver urea of varying quality to the corn crop accurately from one end of its boom to the other, the AirMax expands application windows,” Mohr concludes. “The system can keep you up and running in more varied conditions while also applying the correct rate over more of the field. It’s a win-win.”