Everyone was looking for record or near-record corn yields as harvest approached in 2016. Some fields did yield well. However, the overall line on corn yields in the eastern Corn Belt seemed to be OK to good — and not as good as expected. Late-season diseases were a factor in some areas in lower yields, but some people believe there may have been another reason, too.

“Nighttime temperatures tended to be warmer than normal during the 2016 growing season during the reproductive period,” observes Jon Peacock, Winchester. Peacock, an Indiana Certified Crop Adviser, also farms and operates a DuPont Pioneer seed dealership with his son, Shane, and son-in-law Kevin Kouns. At one time he was a sales agronomist for Pioneer, and before that served as a county Extension educator in Ohio. A Purdue University graduate, corn physiology is something Peacock understands very well.

Respiration factor
Corn yields were relatively good where Peacock farms, but yields for some of his customers weren’t as high as anticipated in 2016, he notes. He says it was drier during key periods in some areas. “We received a rain in July that some people didn’t get,” he says.

“I believe warmer-than-normal nighttime temperatures during the reproductive stage last year were a bigger deal than many people thought,” Peacock explains. “When it’s warm at night, respiration continues inside the corn plant. It doesn’t get to rest as it does when nighttime temperatures are cooler.

“The result is often some impact on yield. Part of the sugars that would normally go into the kernel are used up through respiration at night.”

Peacock points to previous years with cooler-than-normal temperatures, especially nighttime temperatures, during July. Corn yields turned out well in most of those years, he notes.

Second factor
DuPont Pioneer issues an Agronomy Sciences Research Summary each year. One of the articles in the 2016 summary discusses the effect of high night temperatures on corn. Nanticha Lutt, Mark Jeschke and Stephen D. Strachan summarized research about how and why warm nights affect corn.

Their conclusion? The effect is real, and there are two possible explanations. As Peacock noted, increased respiration is one factor. “There is less sugar available for deposition as starch in the kernel,” they note.

The second factor is related to how quickly plants mature. “Higher temperature accelerates the phenological development of the corn plant, so the corn plant matures sooner,” according to the Pioneer researchers. Basically, a faster rate of development means a shorter grain-fill period, which works against higher yields.

In fact, the researchers say that based on their observations, accelerated development of the corn plant due to warmer nights may actually be the primary cause of lower yields, although higher respiration still is a contributing factor. Corn is considered a tropical plant, originating in Mexico. So why would warm nights work against higher yields? The Pioneer researchers point out that in the Central Highlands of Mexico, where corn evolved, days are warm. However, nights are cool. That may help explain why modern hybrids prefer cooler nights for top performance.