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Corn Watch: Know what you’re looking for when scouting in late summer.

Tom J. Bechman, Editor, Indiana Prairie Farmer

August 15, 2023

3 Min Read
A close-up eye-level view between rows of light green cornstalks
PALE GREEN: When there is a significant nitrogen shortage, corn may be pale green like this corn from early in the season. This corn suffered because wet soils allowed applied N to volatilize.Photos by Tom J. Bechman

Does your corn have enough nitrogen to finish the year? Perhaps this is the better question: How will you know if corn has enough nitrogen, or if it runs out before kernels reach physiological maturity, also known as black layer?

“It’s another reason why you want to scout fields in late summer,” says Dave Nanda, director of genetics for Seed Genetics Direct, sponsor of Corn Watch ’22. “If your corn remains dark green until near the end of the season, then you probably have all the nitrogen you need. But if you start noticing symptoms of nitrogen deficiency, then you may want to rethink your nitrogen program for next season. The kicker, though, is that since the weather is different every year, how plants respond to nitrogen is also different every year.”

Nitrogen deficiency symptoms

Here are classic symptoms of nitrogen deficiency in corn. Refer to the Purdue University Corn and Soybean Field Guide for more information.

Pale green color. If corn doesn’t develop that vibrant, dark green color during the season, it may be because nitrogen has been low all year long. In extreme cases, corn will even turn yellow from lack of nitrogen. More often, it’s pale green.

Plants will produce ears, Nanda says. “They just won’t be as long, and they may not be as big around,” he says. “That’s why yield estimates fall off quickly when nitrogen is lacking.”

Related:Two isn’t better than one in corn

How much yield can you lose? “Two years ago, we checked a field where some places were fine, but others were pale green all year due to wetness and lack of nitrogen,” Nanda recalls. “Yield checks showed a 90- to 100-bushel-per-acre yield hit for having pale-green, N-deficient plants.”

Classic leaf firing. This can literally look like the leaf is on fire. It starts at the tip and goes down the midrib in the center of the plant. As the plant continues to be deficient, leaf tissue dies and becomes brown. Losing that much leaf area for photosynthesis contributes to the plant’s lowered ability to produce yield.

corn leaf showing leaf firing symptom

Lower leaves with symptoms. Usually, the lower, older leaves in the canopy will fire first. That’s not just because there is a lack of light low in the canopy. If the classic firing is occurring on lower leaves near the ground first, it’s directly related to the plant’s inability to obtain as much nitrogen as it needs. Lower leaves tend to show it first.

“Look down under the leaf canopy and see what you can find,” Nanda says.

looking down row of green corn below the canopy

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About the Author(s)

Tom J. Bechman

Editor, Indiana Prairie Farmer, Farm Progress

Tom J. Bechman is editor of Indiana Prairie Farmer. He joined Farm Progress in 1981 as a field editor, first writing stories to help farmers adjust to a difficult harvest after a tough weather year. His goal today is the same — writing stories that help farmers adjust to a changing environment in a profitable manner.

Bechman knows about Indiana agriculture because he grew up on a small dairy farm and worked with young farmers as a vocational agriculture teacher and FFA advisor before joining Farm Progress. He works closely with Purdue University specialists, Indiana Farm Bureau and commodity groups to cover cutting-edge issues affecting farmers. He specializes in writing crop stories with a focus on obtaining the highest and most economical yields possible.

Tom and his wife, Carla, have four children: Allison, Ashley, Daniel and Kayla, plus eight grandchildren. They raise produce for the food pantry and house 4-H animals for the grandkids on their small acreage near Franklin, Ind.

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