WHO KNEW? Corn Sweat

The unusual heat waves we have been experiencing this summer combined with humidity has made our end of summer days more uncomfortable than usual in our area.  Like a lot of people, I have just assumed that it is mostly due to the off and on rainstorms we have been having.  Have you ever heard of evapotranspiration (ET)?  ET is caused by evaporation of water from surface soil or plants, specifically corn.  Due to this natural process, we are experiencing lots of “corn sweat” due to the large fields of corn crops around us and across the midwestern states. 

Corn Sweat occurs as temperatures warm up and the plants open their pores to bring in more oxygen.  This then releases carbon dioxide and water into the air.  As the water evaporates it cools the plants with “Corn Sweat.”

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An acre of farmland can grow an average of 177 bushels of corn.  An acre of corn will release up to 3,000-4,000 gallons of water per day into the atmosphere, raising the Dew Points and making the air feel more humid. The humidity level is measured by percentage and is not dependent on the temperature. Dew point is a more accurate way of measuring the moisture content in the air.  Dew point is the temperature where air becomes saturated with water vapor and can no longer hold water in the form of gas. The dew point changes based on the air’s pressure and water content. 

When the air cools to below its dew point, the water vapor condenses into liquid water and can appear as dew, fog or even frost. Dew points ranging 50-60˚F will feel comfortable, whereas above 65˚F can make people feel uncomfortable because they cannot sweat as well.  Dew points above 70˚F can lead to heat advisories. In addition, extreme increases in humidity combined with the stifling air temperatures, flowing up from the Gulf of Mexico, will increase the potential for storm related conditions.

It is estimated that Michigan farmers planned to grow approximately 2.25 million acres of corn this year (2024).  For illustration’s sake, let us round that to 2.0 million acres.  If 50% of those acres released 3,000 gallons of water per day into the atmosphere, we would be looking at three billion gallons of water per day in Michigan alone throughout the state.  This does not include other crops (like soybeans) that will also be adding ET to an already humid atmosphere. Corn tends to add more ET to the atmosphere in July and August, with soybeans adding more than corn during August. No matter how you look at it, even for an ET, that is a lot of corn sweat and humidity!