Corn Sweat and Humidity: A Few Facts Explained

Sep 02, 2024

By Aaron B. Wilson and Alex Lindsey et.al

Every summer, as conditions heat up and humidity levels rise during mid-summer, we hear the phrase “corn sweat.” What is corn sweat and how much does it contribute to the oppressive heat in the summer? As you can imagine, this is a complex question to answer.

First, “corn sweat” refers to the natural process by which plants, in this case corn, move water through the plant to its surface, which then allows this water to evaporate into the atmosphere. For corn, this transition of water from plant to atmosphere typically occurs through the stomata in leaves as well as other surfaces of the corn. Also, when thinking of how much water is associated with a crop like corn, researchers consider two components: water losses from the soil (evaporation) and water losses from the crop (transpiration). Scientifically, we call this combined process evapotranspiration (ET). Some research conducted by USDA Agricultural Research Service suggests that corn can contribute between 3,500 and 5,000 gallons of water per acre to the atmosphere over the course of one to two days. A typical pool contains 18,000 - 20,000 gallons.

There are many factors at play when thinking of how much water in the atmosphere is tied to plants. Research conducted by the Illinois State Climatologist, Trent Ford, showed that local ET contribution plays a role in low level humidity, especially on extremely hot days[1]. However, when compared to moisture brought into the region, typically due to southerly or westerly winds (e.g., from the Gulf of Mexico), this local ET is order of magnitude smaller than the contribution from the large-scale atmospheric flow. This suggests that while the corn contribution to low level humidity is a factor, it may not be the most abundant source. Indeed, we need a more robust analysis of moisture budgets and the contribution from local ET vs. moisture advection (moisture brought in due to prevailing wind patterns). Additionally, even when precipitation deficits are present, water can still be present in mid to deeper layers of the soil and available for the growing crop depending on soil type. Likewise, having a cover on the surface (e.g., a crop) can play a positive role in reducing direct water evaporation losses from the soil, meaning less water moving from the crop to the atmosphere.

Tasseling (VT) and flowering (R1 stage) is the peak of corn water use, and in Ohio, we are well past that point now. From there, water use in corn only decreases (learn more about corn water use here). According to the last USDA Crop Progress & Condition report (week ending 8/25/24), about 90% of Ohio's corn acreage has reached dough stage (R4), 47% of corn was dented (R5), 9% was mature (R6), and 12% of corn silage has been harvested. Much of the national discussion on corn sweat is happening in August, a time when corn begins to significantly scale down its water use as it approaches maturity. Likewise, even when atmospheric demand of moisture is high (like during a hot stretch of weather), corn may not maximize the ET process, and therefore, may not be much of a contributor to the humidity. Recent published modeling work suggests high temperatures (above 86°F) paired with low relative humidity are more detrimental to crop yield as compared to high temperatures paired with high humidity, and suggests extreme temperatures decrease yields indirectly due to limited moisture availability[2].

For Ohio in 2024, much of the state has seen precipitation deficits during the growing season, with only pockets of heavy rainfall. In fact, much of southern and southeast Ohio are experiencing the worst drought conditions in over a decade. Ohio just hit some of the warmest high temperatures of the summer with very little rainfall over the past 7-10 days, and drought conditions are expanding while corn is shutting down. While humidity levels have been high across the central plains and western portions of the Corn Belt, humidity has been much lower across the dry areas here in the east.

With all this information in mind, it is very unlikely that “corn sweat” is contributing in any meaningful way to the recent stretch of muggy days. Instead, the current humidity is driven by more significant climate patterns such as large-scale atmospheric flows and its moisture advections (e.g. regional wind patterns). Here’s to hoping for some relief (and rain) ahead.

Special thanks to Dennis Todey (Director of the Midwest Climate Hub) and Trent Ford (Illinois State Climatologist) for their insightful conversations on corn’s impact on ET and low level humidity.

Source : osu.edu

Video: Why Your Food Future Could be Trapped in a Seed Morgue

In a world of PowerPoint overload, Rex Bernardo stands out. No bullet points. No charts. No jargon. Just stories and photographs. At this year’s National Association for Plant Breeding conference on the Big Island of Hawaii, he stood before a room of peers — all experts in the science of seeds — and did something radical: he showed them images. He told them stories. And he asked them to remember not what they saw, but how they felt.

Bernardo, recipient of the 2025 Lifetime Achievement Award, has spent his career searching for the genetic treasures tucked inside what plant breeders call exotic germplasm — ancient, often wild genetic lines that hold secrets to resilience, taste, and traits we've forgotten to value.

But Bernardo didn’t always think this way.

“I worked in private industry for nearly a decade,” he recalls. “I remember one breeder saying, ‘We’re making new hybrids, but they’re basically the same genetics.’ That stuck with me. Where is the new diversity going to come from?”

For Bernardo, part of the answer lies in the world’s gene banks — vast vaults of seed samples collected from every corner of the globe. Yet, he says, many of these vaults have quietly become “seed morgues.” “Something goes in, but it never comes out,” he explains. “We need to start treating these collections like living investments, not museums of dead potential.”

That potential — and the barriers to unlocking it — are deeply personal for Bernardo. He’s wrestled with international policies that prevent access to valuable lines (like North Korean corn) and with the slow, painstaking science of transferring useful traits from wild relatives into elite lines that farmers can actually grow. Sometimes it works. Sometimes it doesn’t. But he’s convinced that success starts not in the lab, but in the way we communicate.

“The fact sheet model isn’t cutting it anymore,” he says. “We hand out a paper about a new variety and think that’s enough. But stories? Plants you can see and touch? That’s what stays with people.”

Bernardo practices what he preaches. At the University of Minnesota, he helped launch a student-led breeding program that’s working to adapt leafy African vegetables for the Twin Cities’ African diaspora. The goal? Culturally relevant crops that mature in Minnesota’s shorter growing season — and can be regrown year after year.

“That’s real impact,” he says. “Helping people grow food that’s meaningful to them, not just what's commercially viable.”

He’s also brewed plant breeding into something more relatable — literally. Coffee and beer have become unexpected tools in his mission to make science accessible. His undergraduate course on coffee, for instance, connects the dots between genetics, geography, and culture. “Everyone drinks coffee,” he says. “It’s a conversation starter. It’s a gateway into plant science.”