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Midseason input choices can impact kernel size, yield

Tom J. Bechman 3 shucked ears of corn in a row
IMPACT ON YIELD: Some genetics favor bigger kernel size, but all hybrids benefit when the grain fill period results in larger kernels vs. smaller kernels.
Corn Illustrated: Nitrogen and fungicide decisions could affect kernel size.

Some ag economists have suggested farmers might consider cutting back on nitrogen and perhaps skipping fungicide applications on corn to hold down input costs in 2022. What do agronomists say about that strategy?

If your personal crop budget is tight, you may have to do what is necessary, but most agronomists caution that some input decisions could impact yield. And if you reduce yield potential, how many bushels of $6.50 to $7 corn are you willing to give up?

Yield components

“Yield relies on three components: number of ears per acre, number of kernels per ear and kernel weight or size,” explains Brian Denning, a technical agronomist for Stewart Seeds. “It’s a three-legged stool, with each leg being critical. Yield can flow both ways between each part of this equation.”

Denning and Brad Schottel, with Bayer Crop Science, began wondering, even before input prices went out of sight, if they could influence kernel size by adding more nitrogen in mid- to late season, and by applying fungicides. They set up a field trial in 2021 to look at this question.

“We know that beginning about two weeks after pollination, kernels build the factory to hold starch,” Denning says. “The kernel is the factory. Then throughout grain fill, starch produced by the plant fills the factory.

“We also know that about 60% of the starch produced during this period comes from photosynthesis from the ear leaf. The next most important leaves are the ones just above and just below the ear leaf. That’s why it’s critical to protect these leaves from foliar diseases.”

Schottel adds, “This is when hybrids drive yield by adding to kernel depth. Kernel size and depth are extremely important for yield.”

Driving yield

The trial in 2021 indicated that when they added nitrogen and fungicide at the proper times in midseason, yields went up. At that point, ear size in terms of number of kernels per ear were already decided. The number of ears per acre were also fixed at that point.

“What we were adding was more kernel size,” Denning says. Grain moisture also went up as yield increased, but moisture only increased by a relatively small amount, they note.

Space constraints kept them from including a treatment of fungicide only without nitrogen so they could make more concrete comparisons.

“We intend to do the trial again in ’22, and we will add treatments with fungicide but no nitrogen added at midseason,” Schottel says.

Based on results from one season, there is an indication that nitrogen to provide fuel for making more starch and fungicide to protect the primary leaves that fill the factories are good investments, Denning says.

If you’re leaning toward not applying more nitrogen, even if your total N applied rates might be on the low side, and if you are considering skipping fungicide applications, remember there could be consequences, they note. Grain fill is most successful in producing larger kernel size and more kernel weight when it has good weather conditions. But good weather helps only if each plant has enough nutrients to work with, and ample healthy leaf area to produce more starch.

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