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Hot nights rob corn yields

Hot, dry daytime conditions aren't the only things knocking this year's corn crop away from its full yield potential so far this spring. Once the sun goes down, in some areas, it's just as troubling to the crop.

A recent study looking at 20 years of crop and weather data in the Corn Belt reveals just how much damage nighttime heat stress can inflict on a growing corn crop, especially during critical points in the growing season like pollination and grain fill. Researchers at The Climate Corporation have found that in the last 2 decades, there's been a direct correlation between every degree above 72 degrees Fahrenheit during nighttime hours and the amount of yield potential that's lost, according to The Climat Corporation's director of agronomic research, Jeff Hamlin.

"When nighttime temperatures do not fall below approximately 72 degrees Fahrenheit, the corn plant doesn’t get a chance to slow down at night and instead keeps metabolizing sugars at a high rate around the clock. This high rate of nighttime metabolism, often referred to as ‘dark respiration,’ causes the plant to finish the grain fill period and reach full maturity faster than normal," Hamlin says. "Unfortunately the higher rate of dark respiration also causes the plant to put photosynthetic sugars into plant growth and maintenance that would otherwise be used to fill grain and create higher yields. Every sugar that goes into plant growth and maintenance rather than into production of kernel dry matter represents lost yield potential for the plant."

In the group's study, it shows that the Illinois corn crop has seen yields dip by 3.6 bushels/acre for every 1-degree increase in average nighttime temperature during the critical grain fill period. For Indiana, 2 bushels/acre are lost for every degree above 72 at night, on average.

Nighttime temperatures, for a couple of reasons, make up an even bigger factor to yield potential this year than normal, Hamlin says, for a couple of reasons. First, a lot of corn fields were planted earlier than normal this spring, so they'll enter grain fill earlier. Then, there's the heat and dryness that's slammed parts of the Corn Belt so far this growing season.

"An early planted crop will pollinate early and then start grain fill earlier than usual. This will push the grain fill period into a hotter period than normal. If you were trying to manage nighttime heat risk as your primary goal, you would probably want to plant later than normal and have your corn filling grain later in the season then normal when temperatures are cooler," Hamlin says. "Think 2009. Delayed planting led to delayed grain fill which matched up with cool temperatures during grain fill which led to record yields in most places. But given that this risk is less important to yield than heat during pollination, early freeze or drought, it isn't one that growers are going to change practices to manage."

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