Rethink Fall N in Wheat

ROCKVILLE, Md. (DTN) -- With nitrogen supplies tight and costs skyrocketing, there's never been a better year to take advantage of wheat's minimal fertilizer needs in the fall.

Take it from Marc Arnusch, a Colorado farmer who discovered he was overfeeding his wheat crop with nitrogen, in an effort to get the crop up and headed toward its optimal yield.

"We used to put nitrogen on in the fall religiously," recalled Arnusch, who farms in Keenesburg. "We wanted to provide a stocked refrigerator for the crop to pull from in the fall, winter and early spring."

Then, with the help of soil sampling, Arnusch discovered something surprising: The fridge was already full.

Most of his wheat is planted after corn silage crops, and the wheat plants were finding plenty of residual nitrogen to draw from, especially in the dry falls his region has seen in the past decade. Now, the only nutrient he applies at planting is phosphorus.

The reality is that fall-emerging winter wheat doesn't need too much nitrogen, confirmed Dorivar Ruiz Diaz, a Kansas State agronomist who specializes in soil fertility and nutrient management.

"One thing we see pretty consistently is that nitrogen uptake in the fall and winter is no more than 30 to 35 pounds," said Ruiz Diaz. "And depending on when we plant and how much biomass we get, that could be as low as 15 to 20 pounds taken up in the fall and winter."

Soil tests this fall can be a huge help to wheat farmers who are trying to navigate the challenging fertilizer market right now, Ruiz Diaz added. "To me, soil testing is key," he said. "Because, in many cases, that 30 to 35 pounds will already be there, especially in dryland situations where we don't always have excellent summer crop yields and we have some residual nitrogen left there."

That residual nitrogen can come from many places, added University of Missouri emeritus professor of nutrient management, Peter Scharf. "It could be left over from a corn crop; it could have mineralized while soybeans were growing, and they didn't grab it -- it doesn't take much to come up with 15 pounds of nitrogen," he explained. And unless you have very sandy soils, where rain can move nitrogen rapidly down through a soil profile, those nutrient leftovers should remain available to a fall-planted wheat crop, Scharf added.

When wheat wakes from its winter slumber, it's a little hungrier. That's when Arnusch rushes to the field with the crop's first serving of nitrogen and streams on 45 to 50 lbs. The key is to get it on before the jointing stage, when a plant's nitrogen appetite skyrockets. He gives another big helping at early flag leaf.

"We think of it like leading a receiver on a football field -- we try to throw to where the crop is going to be shortly, not where it is right now," he explained.

His wheat isn't complaining. In 2019, Arnusch grew an award-winning field of irrigated winter wheat that topped out at 210 bushels per acre (bpa). Nor has his farm's overall winter wheat average yield suffered without fall nitrogen applications; it ranges between 55 bpa on the dryland and 130 bpa under irrigation.

That's something Scharf wants more wheat farmers to examine. Last year, he analyzed a series of field experiments at four different locations in Missouri over two years. Nitrogen was either applied all at planting, all in the spring, or it was split -- with a third going on in the fall and two-thirds in the spring. The researchers tested two rates: 80 lbs. and 120 lbs.

Seven out of eight times, putting all the nitrogen on in the spring showed no significant yield penalty, Scharf said. Only once did a split application -- one-third applied in the fall and two-thirds in the spring -- produce a yield bump compared to the other applications, a 3-bpa gain. That gain would not cover the extra cost and effort of a nitrogen application across the field every fall for all eight years, Scharf noted.

In fact, as long as nitrogen is in place before the jointing stage, growers are unlikely to see any yield penalties for skipping a fall application, Ruiz Diaz and Scharf said.

Of course, yield isn't the only factor at play for farmers using fall nitrogen applications.

Growers who graze livestock on fall winter wheat stands have a different goal: maximum biomass, as quickly as possible. For them, putting all or most of their nitrogen on in the fall is the better management strategy, Ruiz Diaz noted.

Putting nitrogen on in the fall can also free up time in the spring, when fieldwork gets busy and the windows of good weather can be scarce. This year, the uncertainty of spring supplies also has growers favoring fall nitrogen applications, simply to be sure of getting the nutrients on while it is available. And in the semi-arid regions of the country, such as eastern Colorado and western Kansas, you're less likely to lose much fall nitrogen to leaching, Ruiz Diaz said.

But then again, those are places where nitrogen is also likely to remain available to growers in the fall from summer crops, without any fertilizer applications. And although spring supplies and prices remain uncertain this year, in general, moving to spring applications may help dryland farmers utilize Arnusch's strategy of keeping resources out of the field until they're most likely to pay off, Ruiz Diaz added. "A lot of our farmers in western Kansas head to the field in February and March and evaluate what is out there -- do we have the moisture and yield potential to invest more in this crop?"

As you move into higher-moisture environments, where nutrient leaching is more common, the benefits of moving nitrogen applications to springtime become even more evident, Scharf noted. In some states, regulators have taken note, and are pushing growers to deliver nutrients in season, when nutrient loss is less likely. (See DTN story here: https://www.dtnpf.com/….)

For growers who are considering moving away entirely from fall nitrogen applications in wheat, or moving their spring applications closer to the critical jointing stage, Scharf has one final piece of advice: Have a backup plan.

Arnusch is able to stream on much of his nutrients via irrigation pivots, but most farmers need to make sure they have the equipment to tackle spring applications, with all the weather complications that come with them.

"Have a backup plan to do it with something other than your usual equipment," Scharf said. "Maybe it's older, lighter sprayers you can use on wet ground, maybe it's a plane -- just don't get caught with a year of no nitrogen applications."

See more on the Missouri nitrogen experiments here: https://ipm.missouri.edu/….

Editor's Note: This story was originally published on Nov. 6, 2020, and is being reprinted for the 2021 season. See the original here: https://www.dtnpf.com/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow her on Twitter @Emily_Unglesbee

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