All the talk as far as sub-par corn yields this year has been related to either late planting, hot, dry weather during pollination or very dry conditions in some areas. There may be one other factor working against maximum corn production high nighttime temperatures.
One year ago when the corn crop was respectable, many believe this was a factor. In fact, People like Arlan Suderman, Farm progress market specialist, suspect it played a major role in USDA's near-record lowering of the estimate f the size of the corn crop from the initial estimate in August to the final estimate for the year in January. It was a drop of more than 10 bushels per acre.
Suderman worked with research companies last summer to compile data going back decades. Their conclusion was that in year's with high nighttime temperatures in the summer, USDA estimates tend to drop form August until the final estimate.
What's going on here? Suderman says it's because plants need time at night to cool down and convert energy captured during the day into sugars. However, if temperatures stay too high, the plant continues to respire and uses up some of the energy it made in that process. Otherwise, that energy would be directed toward the corn kernel.
Most studies that have been done on this phenomenon peg the nighttime low breaking point at about 65 degrees F. if temperatures average above that level during the critical grain filling period, than yields may suffer as well. The plant simply doesn't have as much sugar to convert into starch and pack into the kernels, because instead it burns it up to keep the plant going through the night.
Several lows in the mid-70s and at least one low in the mid-80s in July in central Indiana, according to the National Weather Service, likely worked against corn, instead of adding to yield.It will be interesting to see if the USDA adheres to any of these observations, or last year's outcome when issuing its first crop report this week. Typically, July crop reports are more about plant count at the randomly-selected that enumerators for USDA visit than about anything else. Your guess is as good as ours whether they will make any adjustments or not in their estimation procedure for this year.