Yes, 'corn sweat' is real and it can make for sweltering summer days

Donnelle Eller
Des Moines Register

Editor's note: This story by Register reporter Donnelle Eller was originally published in July 2016. Dates and weather references have been updated. 

It's not the heat, Iowa, it's the corn sweat.

Yes, one of Iowa's most well-known crops could take some blame for some miserably hot and humid summer conditions. 

No, the nation's 90-plus million acres of corn don't really sweat, Mark Licht, an Iowa State University Extension agronomist, said in 2016. But they do transpire moisture — or water vapor — as they drink in massive quantities of water through their roots deep in the ground, Licht said.

At the same time, corn plants breathe in air, absorbing carbon dioxide and converting it into sugar that enables them to grow.

More:About a third of Iowa counties are in moderate droughts, 11 are in severe droughts

Right now is a peak time for water use, with corn plants pollinating and forming rows of kernels within developing ears. The hotter the temps get, the more transpiration — or corn sweat — that occurs, Licht said.

Harry Hillaker, the now-retired state climatologist, said Iowa's 14 million acres of corn, and its more than 9 million acres of soybeans, add to Iowa's humidity.

"All vegetation does, to some degree," including soybeans, trees, shrubs and lawns, he said.

During the growing season, an acre of corn sweats off about 3,000 to 4,000 gallons of water each day, according to the U.S. Geological Survey.

Iowans grow corn, soybeans and other crops on about 25 million of the state's 36 million acres.

"We'd be humid, anyway, but we're more so with the row crops that we have," said Hillaker.

"The warmer the air is, the higher the capacity it has to hold moisture. That can increase very dramatically as it gets warmer."

More:12 ways Iowans have beaten the heat throughout the years

Hillaker said Iowa's soils can hold as much as a foot of water, which helps crops grow in the summer. He said Iowa's humidity isn't affected much by shifts in the acres planted between corn to soybeans.

"The numbers are pretty stable year to year. It might be a million acres here or there, but percentage-wise, it's not that large of a change," Hillaker said.