Warm Nights Can Hurt Pollination

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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The good old summertime may, at times, not be so good for crop development--especially when new kernels and seeds are forming and filling. Research on corn growth and development indicate that, during the fill stage of the crop, overnight low temperatures in a range of 62ºF to 74ºF (17ºC to 23ºC) are ideal. But, when that range is surpassed over a period of several days--or for large portions of the season--there can be some yield loss potential

A University of Nebraska-Lincoln Cropwatch article on how very-warm overnight low temperatures can affect corn pollination is just one of many summaries on this topic. Here is an excerpt:

“In years when we get high day and nighttime temperatures coinciding with the peak pollination period, we can expect problems. Continual heat exposure before and during pollination worsens the response … high humidity, which helps reduce crop water demand, also increases the thermal mass of the air--and provides extra stored heat and insulation at night.

“Corn is a ‘C4 Photosynthesis’ plant, making it extremely efficient at capturing light and fixing CO2 into sugars. One drawback of this system is that with high daytime temperatures, the efficiency of photosynthesis decreases, so the plant makes less sugar to use or store. High nighttime temperatures increase the respiration rate of the plant, causing it to use up or waste sugars for growth and development. This results in the plant making less sugar but using up more than it would during cooler temperatures.”

Other research into this topic, done by Dr. Peter Thomison of Ohio State University and summarized in the Monsanto “Agronomic Spotlight,” points to the 70ºF to 80ºF degree threshold at night as being tough for corn, with higher respiration rates and lower dry matter accumulation. Thomison’s findings indicate that respiration rates may double for each 13-degree Fahrenheit increase in temperature, as the corn plant uses more of its sugars produced during photosynthesis simply to stay alive. This means, in turn, less energy available for the developing kernels.

The bottom line is, pollination or flowering weather conditions comprise only a portion of the critical reproductive time frame for crops. And in the case of corn, hot summer nights may simply force the plant to work overtime, and limit the contribution toward the final product--the kernel at harvest. This is a detail that my colleagues and I in the DTN/Progressive Farmer ag weather team will be keeping close track of as we go through late summer.

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