Low night temperatures during the grain fill period (which typically occurs in July and August) have been associated with some of our highest corn yields in Ohio. The cool night temperatures may have lengthened the grain fill period and reduced respiration losses during grain fill.
High night time temperatures result in faster heat unit or growing degree day (GDD) accumulation that can lead to earlier corn maturation, whereas cool night temperatures result in slower GDD accumulation that can lengthen grain filling and promote greater dry matter accumulation and grain yields. This is thought to be the primary reason why corn yield is reduced with high night temperatures.
For example, let’s say a hybrid needed 1350 GDDs to reach maturity after flowering. With an average daytime temperature of 86 F and average night temperature of 68 degrees F, it would take 50 calendar days to accumulate 1350 GDDs. Conversely, with a day temperature of 86 F and a night temperature of 63 F, it would take 56 calendar days to reach that same GDD accumulation.
This means with cooler nights, the corn plants in this example would get six additional days to absorb light for photosynthesis and water for transpiration, which could result in increased yield. Research at the University of Illinois conducted back in the 1960s indicated that corn grown at night temperatures in the mid-60s (degrees F) out yielded corn grown at temperatures in the mid-80s (degrees F).
Cooler than average night temperatures can also mitigate water stress and slow the development of foliar diseases and insect problems.
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Night temperatures can affect corn yield potential. High night temperatures (in the 70s or 80s degrees F) can result in wasteful respiration and a lower net amount of dry matter accumulation in plants. Past studies reveal that above-average night temperatures during grain fill can reduce corn yield by reducing kernel number and kernel weight.
The rate of respiration of plants increases rapidly as the temperature increases, approximately doubling for each 13 degree F increase. With high night temperatures, more of the sugars produced by photosynthesis during the day are lost; less is available to fill developing kernels, thereby lowering potential grain yield.