Ag Weather Forum

Warm Lows Hurt Yields

Bryce Anderson
By  Bryce Anderson , DTN Senior Ag Meteorologist
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Research findings continue to show that high nighttime temperatures can put a big crimp on corn yields during the time after pollination. (DTN photo by Bryce Anderson)

A research summary article called "High Night Temperature Effects on Corn Yield" compiled by DuPont Pioneer is being circulated at the farm shows this winter. The occurrence of -- and likelihood to continue -- of high nighttime temperatures is one of the primary features of the impact of climate change brought on by global warming as widely measured and noted.

The DuPont Pioneer study specifically reviewed the July and August average overnight low temperatures in 2009 and 2010 in Nebraska, Kansas, Iowa, Missouri and Illinois, and then compared the corn yield difference in these two crop years, using USDA NASS yield numbers.

(It needs to be noted that this study is not the first or only one that has been done on this feature. The study of high nighttime low temperature influence on corn yields goes back more than 40 years, to lab experiments at the University of Illinois.)

The temperature and yield difference numbers are striking. They show a big yield drop-off in 2010 versus 2009, when the July-August average nighttime temperatures were five to seven degrees Fahrenheit above 2009. The July-August time period was used in order to track the impact of temperatures on corn production after pollination. Here's the rundown:

State 2009 2009 Yield 2010 2010 Yield Yield Change
NE 57 179 62 166 -13
KS 62 155 67 124 -31
IA 58 181 65 165 -16
MO 62 153 68 123 -30
IL 60 174 66 157 -17

These are notable declines in yield. There are two reasons for this warm nighttime effect given as possibilities. The first is that the warm overnight weather forces the corn plant to withdraw sugars from the developing corn kernel in order for the plant to maintain itself, because there is no respiration period for the plant with this temperature regime. A second reason, and one which is getting more acceptance as the primary reason for such a drop-off in yield, is that the higher nighttime temperatures shortened the time period between pollination and plant maturity, which meant fewer days for photosynthesis to take place.

Quoting from the DuPont Pioneer article: "The majority of the research generally shows that accelerated phenological (seasonal or cyclic) development is likely the primary mechanism by which high night temperatures can negatively affect corn yield. Faster plant development reduces the total amount of photosynthesis carried out by the plant during reproductive growth. In additional, photosynthesis per unit of thermal time during the critical period following silking decreases. Consequently, high night temperatures can affect both kernel number and kernel weight depending on timing and duration of heat stress."

I emphasize that last sentence.

The authors of this DuPont Pioneer article are: Nanticha Lutt, Agronomy Sciences Intern; Mark Jeschke, Ph.D., Agronomy Information Manager; and Stephen D. Strachan, Ph.D., DuPont Research Scientist.

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