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Can a late season nitrogen application help corn yields?

Some areas of corn country could boost yield with a late shot of N.

Areas of the Corn Belt are woefully short on moisture, while in others, the corn crop looks surprisingly good thanks to timely rains. Yet, some farmers in some fringe areas of the Corn Belt don’t always apply enough nitrogen prior to emergence to capitalize on excellent growing conditions. 

The scenario

The July 22 Crop Progress Report from USDA’s National Agricultural Statistics Service (NASS) shows nearly 90% of the U.S. Corn Belt is in very good to excellent yield condition. Most of the crop is in the midst of the reproductive stage (silking to dough stage, depending on geography). By this time, the corn plant has accumulated about 70% of the total nitrogen it needs, according to Purdue University research. The remaining 30% of its N needs will come from a combination of corn stem and leaf tissue, and new N. 

Moisture is the most limiting factor in many areas of the western Corn Belt. For example: In Jewell County, Kansas, in the north-central part of the state, the 2019 corn yield was 145 bushels per acre, according to USDA’s National Agricultural Statistics Service (NASS). Most farmers fertilized for a similar yield goal for 2020. Yet, since May 1, the area has received from 13  to 20 inches of rain – pushing potential yields higher than that 145-bushel-per-acre yield goal.

Thus the question: Can a late-season application of nitrogen help these farmers maximize yield?

Dorivar Ruiz-Diaz, Extension fertility specialist at Kansas State University, says it’s possible. 

Research that he and his KSU colleagues have done shows that nitrogen applied at VT-R1 can bump yield in a scenario where nitrogen is short.

In three years of research, the group had four plots:

  • Control (0 pounds N)
  • 150 pounds preplant
  • 100 pounds preplant and 50 pounds at V6
  • 100 pounds preplant and 50 pounds at V10

Postapplications of nitrogen featured UAN, drippled between the rows. 

Across eight sites, the three-year average yield gain was 9 bushels per acre, with the late-split applicaton of N vs. all preplant. 

There is a caveat, however. Ruiz-Diaz says the experiments were conducted in areas where there was a high risk of nitrogen loss applied preplant. 

Still, the premise is the same as our scenario above: If farmers didn’t apply enough nitrogen on their corn, they can apply nitrogen late to capitalize on promising growing conditions. 

“I think we can have situations where dryland fields were fertilized for 120- to 130-bushel-per-acre corn and now expectations are closer to 180 bushels per acre. There likely isn’t enough nitrogen to reach that yield,” Ruiz-Diaz says. “In Kansas, when we have good years, maybe we end up a bit short of nitrogen. I see this one situation where late-season nitrogen can pay, as long as we get the rain to incorporate it.”

The specialist says R1 – the silking stage – is about as late as one should apply supplemental nitrogen. 

“At R1 we have the number of kernels formed (pollination), but after this stage, all we have is kernel weight. The chance of yield increased is much more limited then, as all you can do is increase kernel weight,” he says. 

With very late applications – or those after R1 – there may be an increase in nitrogen in the grain, meaning the plant is still taking up nitrogen, but the added nitrogen occurs too late to actually add bushels.  

How to apply late N?

Ideally, farmers can use high-clearance applicators to apply nitrogen, says John Sayer, fertility specialist at Iowa State University. If those aren’t available, some agronomic companies apply UAN with an airplane as a last resort. 

“While all product/method/timing options may not be ideal, not getting N applied is a much greater concern,” Sawyer says. 

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