LEXINGTON, Ky.— With speculation corn is impacting humidity and a higher heat index across the Midwest, University of Kentucky Grain and Forage Center of Excellence director and grain crops specialist Chad Lee provides numeric data on the water loss from America’s most prolific crop.
Corn can emit 4,000 to 8,000 gallons of water per acre per day through the process of transpiration, Lee said. This is actually only a small addition to existing moisture and decreases as ambient humidity increases.
By Jennifer Elwell, UK Agricultural Communications
“In these current conditions, there are about 160,000 gallons of water in the air already. So, any water coming from a field of corn is negligible to the total amount of water in the air,” Lee said. “Corn is not making your days more humid unless you are walking in corn fields all day.”
Corn, like all plants, transpires water and oxygen to help maintain plant functions, Lee explains. Once the corn plant leaves cover the rows and intercept most of the sunlight, most water loss from the cornfield comes from transpiration.
Water loss from transpiration is influenced by water availability in the soil, the amount of water in the plant, relative humidity (which is the amount of water in the air), air temperature, cloud cover and wind speed.
“If the relative humidity (RH) is high, then transpiration (water loss) from the plants is low,” Lee said.
Some estimates in Nebraska indicate that peak water loss from a cornfield is approximately 0.33 inches per acre per day. That equals 8,960 gallons of water per acre per day for approximately 20 days. Estimates east of the Missouri River suggest corn will transpire about 4,000 gallons per acre per day.
“If RH is 50%, and corn plants are at maximum water demand, corn in the region likely loses closer to 5,000 gallons per day,” Lee said. “While that is a large amount of water for any household to use in a day, it is a very small percentage compared to what is already in the air.”
Lee said that determining the amount of water in the air is found by using a psychrometric calculator, which takes into account 86°F and 50% RH at a location’s elevation.
“With these parameters in the Bluegrass Region of Kentucky, there is about 0.0136 pounds of water (H2O) per pound of dry air. That comes to about 160,000 gallons of water above one acre, whether that acre is corn, a football field or houses in town.”
To add more perspective to the volumes of water being discussed, Lee noted that one inch of rainfall is equivalent to 27,184 gallons per acre.
The Kentucky Mesonet at Spindletop Farm in Lexington has recorded 3.1 inches of rainfall for July, equivalent to 84,270 gallons of water per acre that has fallen on the soil. If the atmosphere is holding 160,000 gallons of water at 50% RH and 86 degrees Fahrenheit, and all that water decided to fall to earth in a day, that is equivalent to about 5.9 inches of rainfall per acre.
“Now, if someone walks into a cornfield, that corn will block airflow. As that corn transpires, a person will perspire. Inside that cornfield, it will feel more humid,” Lee said. “But, outside the cornfield in this region of the country, it is unlikely that corn or any other crop will transpire enough water to dramatically affect the humidity in the neighborhoods, towns, and cities.”
Lee also pointed to the benefits of corn for the atmosphere.
“An acre of corn could remove 35,000 pounds of carbon dioxide (CO2) and release about 25,000 pounds of oxygen (O2) per acre over the growing season,” Lee said.
Learn more about corn production in Kentucky and related issues at https://graincrops.ca.uky.edu/corn.
