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NE MO & W IL | Something I wrote last year that addresses your question.....
Grain yield (bushels/acre) is a function of harvestable ears/acre, number of kernels per ear, and the weight of those kernels (not to be confused with test weight). In a typical year, harvestable ears and number of kernels per ear are generally determined by August 1st; however, kernel weight is determined throughout the grain fill period from August into early September. Kernel weight is a function of the plant’s ability to provide readily available and stored photosynthates (sugars and carbohydrates) to the developing ear/kernels. The amount of photosynthates available and the length of the grain-fill period determine the average kernel weight for a given ear of corn.
Now it’s time to do a little plant biology 101. Those photosynthates which create kernel weight originate from the essential plant process called photosynthesis. In photosynthesis, carbon dioxide from the air and water from the soil react with the sun’s energy to form photosynthates, releasing oxygen as a byproduct. The majority of those photosynthates (namely, the sugar, glucose) are used in cellular respiration and the remainder is stored in leaf and stalk tissues or translocated directly to the developing grain for grain fill. Cellular respiration within a plant is the process of converting the sugars (photosynthates) into energy for cell growth, maintenance, and all other life processes within the plant (metabolic processes, transpiration, etc.) Dark respiration, or respiration at night, is the term for the “cellular maintenance” portion and its rate is directly proportional to air temperature as heat speeds up chemical reactions in a plant (kinetic energy). The rate of photosynthesis is also somewhat temperature-dependent and peaks around 86oF (see chart*). So, in a perfect corn world at mid 80-degree daytime temperatures and mid 60-degree nights, plenty of sugars are produced to fuel cellular respiration (both day and night) and keep the grain-fill “storage tank” full, if you will.
What happens when we have 90+ degree daytime temperatures and nighttime temperatures hovering around 80 degrees? As metioned above, cellular respiration, in general, increases creating a need for more sugars, especially during dark respiration. The rate of photosynthesis flattens out (around 86oF) and some research would suggest it may decline. So, when temperatures rise above 86oF, the rate of sugars used by respiration actually rises above the rate at which sugar is manufactured by photosynthesis. This equals a negative net photosynthetic rate and causes a negative impact on the sugars left for grain-fill (see chart**). The bottom line is that higher nighttime temperatures cause the corn plant to burn more sugars than are produced.
High temperatures during grain-fill not only decrease the amount of photosynthates available, but shorten the grain-fill period for those photosynthates to be assimilated into the kernel before black layer formation. The primary driver of the rate of kernel filling is air temperature. When air temperatures are high, sugars from current photosynthesis as well as re-mobilized sugars from leaf and stem reserves go to the ear sink even faster. Grain-fill is a 24-hour, 7-days-per-week process, so both daytime and nighttime temperatures matter. Lower overall temperatures during the grain-filling period, such as those experienced in 2009, and longer grain-filling periods are the preferred conditions for achieving high yields. With a lack of critical photosynthates and a shorter grain fill period, kernel weight and, ultimately, grain yield, suffered in 2010.
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How do warm overnight temps affect corn yeild?
