Corn doesn’t stop working when the sun goes down. In fact, what happens overnight can have a meaningful impact on how much corn you harvest.
As average summer nighttime temperatures rise, agronomists are paying closer attention to the potential yield penalty from prolonged warm nights.
“High night temperatures can be bad for corn yield,” says Mark Jeschke, Pioneer agronomy manager.
Jeschke says the average nighttime lows during June, July and August for the U.S. have increased by over 3 degrees Fahrenheit since 1970.
Research from Pioneer, university Extension and others indicates the risk to corn yield increases when nighttime lows remain above 70°F.
The potential impacts from elevated temperatures at night? At pollination, they can reduce kernel set — the final number of kernels each ear will contain. Later, during grain fill, the heat can limit how much starch each kernel packs on.
More Heat, More Respiration
One reason warm nights can hurt yield outcome is what happens inside the plant after dark, notes Jeschke.
Corn uses cellular respiration around the clock to convert stored sugars into energy for basic plant functions, growth and grain development.
“The main physiological process affected by high night temperatures is cellular respiration,” Jeschke says. “Unlike photosynthesis, which only happens during the day, respiration keeps running all the time, and it’s a temperature-dependent reaction. So, the warmer it is, the faster it goes.”
That creates a trade-off during grain fill. More energy is consumed through respiration, leaving less available for developing kernels.
“When the nighttime temperature increases, the total expenditure of energy through respiration also increases, leaving less energy to contribute to grain fill,” he says. “The higher those night temperatures and the longer they last during grain fill, the more they can take off the top of your yield potential.”
The result, subsequently, is fewer and/or lighter kernels, adds Iowa State’s Mark Licht and Sotirios Archontoulis, in an online article.
Warm Nights Also Speed Maturity
Another way hot nights can trim yield is by pushing corn through its developmental stages faster.
Higher nighttime temperatures contribute to faster Growing Degree Unit (GDU) accumulation. That can shorten the number of days the plant has to photosynthesize and put carbohydrates into the kernels.
Jeschke offers an example for consideration, citing a scenario where the low temperature for the night climbs from 65°F to 73°F.
“That works out to an extra four GDUs,” Jeschke says. “You start adding those GDUs up over multiple days during grain fill, and that plant’s going to mature sooner, which means fewer days of photosynthesis to build yield.”
The result can be a double hit to corn: The plant can burn more energy at night while having less time to build and fill kernels.
Duration Of Higher Temps Matters
Jeschke cautions farmers against thinking of 70°F as the magic number where corn suddenly begins losing yield potential.
The response is typically gradual, and the longer the crop experiences elevated nighttime temperatures, the greater the potential impact.
“Because these effects are incremental and cumulative, it’s difficult to identify a specific temperature threshold at which yields are impacted,” Jeschke says.
Still, extended periods with nighttime lows above 70°F during pollination and through early grain fill, especially, are a useful warning sign for farmers.
“Research suggests that once nighttime lows during grain fill start holding above 70 degrees, we’re probably getting into the danger zone,” he says. “The higher the temperature and the longer it goes on, the more yield can be affected.”
Not Every Hybrid Responds The Same
A valuable thing for farmers to know is that yield impact from higher nighttime temperatures isn’t uniform across hybrids.
A recent Kansas State University field study put 12 commercial corn hybrids under extended elevated nighttime temperatures about 3.8°C (6.8°F) above ambient throughout grain fill. Above ambient means warmer than the surrounding environment or normal environmental temperature.
The Kansas research results, published in 2024, showed 14% reduced yield, 8% reduced kernel weight, and significantly reduced kernel nutrient content, specifically magnesium in the susceptible hybrids.
Protect The Plant’s Yield-Making Engine
While farmers can’t turn down the nighttime thermostat, they can protect the crop’s ability to make and retain yield when hot nights arrive.
Keeping plants healthy through grain fill becomes particularly important. Disease, nutrient deficiencies and other stresses can further reduce the crop’s ability to maintain photosynthesis and fill kernels.
Along with that, farmers’ hybrid selection process could become increasingly important in those areas that regularly experience hot, humid nights.
Understanding how individual hybrids respond to nighttime heat can help growers manage the risk more effectively as growing conditions change, Jeschke adds.
Hear more of Jeschke’s perspective on the impact of nighttime heat on corn at the video link below:
