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Plan for Changes to Corn Fertility Strategy

Winter weather challenges have growers thinking about nitrogen options for corn.

For farmers who didn’t get nitrogen (N) fertilizer on last fall, it may feel like panic time.

But it’s not.

Sure, last fall’s late harvest, coupled with extreme weather since, has made preseason nutrient management more difficult – but not impossible – for the 2019 crop, says Emerson Nafziger, agronomist at the University of Illinois.

“It was wet last fall and that made for a short window to get ammonia applied. And some that was applied was probably into soil on the wet side,” Nafziger says.

Some farmers were able to get into the field late, putting on anhydrous ammonia just prior to and right after the ground froze. It’s not ideal to place anhydrous ammonia into wet soils beneath a frozen surface but it can work all right if spring conditions are good, he adds.

Now, as March approaches, producers are getting anxious to roll again, says Orvin Bontrager, crop adviser for Servi-Tech from Aurora, Nebraska.  

“I’m not panicking yet. If we get some warm days in March, things can dry out pretty fast,” Bontrager says.

That may be of little solace to producers who feel like they’re behind schedule. Bontrager reckons fewer than half the acres typically fertilized with anhydrous ammonia in the fall were actually completed.

Assuming Bontrager’s projection that conditions are right in March, there are some questions that need to be answered. 

Should growers consider split applications?

There’s an old theory that when it’s time to plant corn, plant corn and add N later. “We’re starting to change our tune,” Nafziger says.

The most important factor in applying N is to get at least some of it on in time for plant roots to access the nutrient as the root system begins to develop, he says. It may not be necessary to get all the fertilizer on upfront, but growers should try to get at least half of it on before or right after planting.

According to a 2015 summary from the University of Nebraska, nitrogen use efficiency in corn is improved when roughly 75 pounds of N are applied between fall and spring passes prior to planting, with the rest applied in-season, prior to the eight-leaf stage, for instance.

According to research from Pioneer, more than half the corn’s total nitrogen needs occur between V8 and tasseling (VT). Therefore, in a split nitrogen application, get the rest of the nitrogen on by V4 to V6 to make sure enough N is available to support growth at that time.

It may seem like split applying N is merely kicking the can down the road, but it could help ease a time crunch if March and April stay cold and wet.

Growers equipped to split apply anhydrous could consider using guidance systems to fine-tune that N application closer to the corn row to ensure the nitrogen gets to the plant’s roots. “I suggest 6 to 8 inches away from the row. In heavier soils, where the anhydrous moves a shorter distance from the point of release, it could even be closer,” he says. Applying anhydrous halfway between corn rows is safe, but it isn’t always the best way to apply 100% of the product because it can take the plant’s roots too long to reach N, and result in yield loss.

Is an anhydrous ammonia bottleneck forthcoming?

When it is time to roll, farmers aren’t going to want to wait around for anhydrous ammonia tanks to be filled at their local supplier. Nafziger recalls Illinois producers faced a similar situation going into the spring of 2010. While most suppliers are up to the challenge, the number of supply trips that will be needed and the time that field conditions open up will be important factors to watch play out.

If the window to apply anhydrous opens up in March and lasts a month, most dealers should be fine. But if cold and damp conditions continue past Mid-March, “that’s pretty tough,” he says.

Most dealers are prepared to stay open longer hours to accommodate farmers. A potential bottleneck could create headaches, says Servi-Tech’s Bontrager.

“I don’t have to supply the stuff so I don’t have to worry about it. But you can drain a tank pretty quickly and it takes quite a bit of shuffling tanks around to get them out there,” he says. “I would think there might be a crunch. The product is there, but having enough nurse tanks could be a challenge.”

Are other N sources more appealing?

Retail prices for anhydrous have increased 10% to 15% since last fall, and the potential for supply bottlenecks have some producers considering using other sources of N, including dry urea (46-0-0) or liquid UAN (28% or 32%).

“Some guys are switching more to liquid and planning to apply UAN with herbicide right after they plant,” Bontrager says.

Adding 35 pounds of N is 10 gallons of 32% UAN, a good carrier for herbicide applied right after planting. That’s a good way to reduce the before-planting workload if it’s part of your normal system.

Or, if in-season, get UAN on as close to the row as possible using drop nozzles or Y-Drop-like attachments. Broadcast urea also can be effective, Nafziger says.

However, moving solely to dry or liquid products could be a difficult shift in a system geared up for anhydrous ammonia, Nafziger adds. “Changing source in a major way from what was planned, and doing that on short notice, may not be easy or even possible.” 

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