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When applying nitrogen late helps corn most

Tom J. Bechman nitrogen application on corn
APPLY MORE NITROGEN: If plants are obviously deficient in nitrogen, Jim Camberato says adding N helps, but how much it helps depends on the season. Results for applying N on healthy corn are far more inconsistent.
Corn Watch: Agronomists say a late-season N application helps, but how much depends upon weather conditions.

The Corn Watch ’21 field produced a good yield overall, but several spots where plants were deficient in nitrogen prevented higher yields. The spots were visible when plants were waist-high, and they were pale green with classic symptoms showing at tasseling. These spots corresponded with lighter, somewhat poorly drained areas. Soils were waterlogged off and on from mid-May through mid-July. The field is not pattern-tiled.

The grower added a small amount of nitrogen in a midseason application. The question becomes: Would these spots have benefited from 75 to 100 pounds of nitrogen applied before tasseling?

Related: Separate agronomic grain loss from machine loss

Corn Watch ’21 is an effort to help you learn about what might work for you based on observing a field in central Indiana. Seed Genetics Direct sponsors Corn Watch ’21.

How much help?

Jim Camberato, the Purdue University Extension soil fertility specialist, says the best answer to the question about adding N before tasseling is probably. But he is quick to say that the way the season turned out, with five weeks with virtually no rain from mid-July until mid-August, it’s difficult to tell how much additional N would have helped.

“The challenge is that these mid- to late-season nitrogen applications depend heavily on weather conditions which follow application,” Camberato says. “Based on research dating back to 2010, we don’t see as much benefit in years when it is on the dry side after application versus years when you get timely rains and favorable weather during grain fill.”

Smaller plot experiments in average years showed yield increases of 27, 40 and more than 60 bushels per acre when nitrogen was applied midseason to plants obviously deficient on nitrogen. In a drier year, the first challenge is getting enough rain for nitrogen dribbled on the surface to work, Camberato says. Even if it is injected below the surface where most roots are, you still need rain for better nitrogen uptake.

Bigger payoff

“We saw as much as 110 bushels more per acre in two different years when we applied nitrogen on corn starved for N before tasseling,” Camberato says. “But in both of those years, the rest of the season was near ideal, with good rains helping grain fill.”

When plants are healthy and there are no obvious signs of N deficiency, the results are much more inconsistent, he says. “We’ve seen small increases in yield for extra N in farmer trials some years, but little or no increase in other years,” Camberato adds.

The bottom line, however, is that if plants are truly nitrogen deficient, adding more nitrogen will help, but it’s a question of how much it will help. With increasing prices for N in 2022, it may take a bit more pencil pushing to decide if an extra application would be economical than in the past.

To learn more, check out Late-season nitrogen application for corn. You can also review The effects of late-season nitrogen application for corn.

TAGS: Fertilizer
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