Hot summer nights can hamper corn yield

Suppose you buy green bananas at the store. Are they going to ripen quicker left outside in the summer when it’s warm? Or would they mature faster during the fall if left outside?

Hot summer nights can hamper corn yield

Suppose you buy green bananas at the store. Are they going to ripen quicker left outside in the summer when it’s warm? Or would they mature faster during the fall if left outside?

Obviously, the answer is “summer.” Higher temperatures speed up the biological process of plants and shorten their life span.

Here are two facts. First, corn performs best at moderate temperatures. It does not produce well when it is too hot. Second, this summer has been hot, with more than 30 days of 90 degrees F or higher in some regions of the Corn Belt.

Key Points

• High environmental temperatures speed up the biological process in corn.

• Plants don’t use biomass most efficiently if temperatures are too high at night.

• Plants will sacrifice carbohydrates from other parts if necessary to fill kernels.


During very hot days and very hot nights, corn uses up some of its biomass in wasteful respiration. As temperatures rise, respiration rate increases rapidly. At higher temperatures, carbohydrates made through photosynthesis during the day may be lost.

If some carbohydrates are lost, yield will be lower. You won’t be talking about super-high yields. Irrigators report this phenomenon during warm summers. Even though corn gets plenty of water in those summers, it still does not typically yield as well as in cooler summers.

Corn likes it cool

Cool is relative. Ideally, corn likes it to max out at about 86 degrees F during the day and bottom out at 65 to 70 degrees at night during the midsummer growth phase. Notice that in the Growing Degree Days formula, no credit is given for temperatures above 86 degrees.

The rate of photosynthesis decreases when plants are stressed, compared to ideal conditions. If it’s during the grain-fill period, plants redirect stored photosynthesis products to the grain. They may be pulled from leaves and stalks.

In effect, corn plants sacrifice certain plant parts to meet needs of growing kernels. This can result in weakened stalks. This may be a good year to do the push or pinch test on fields not yet harvested.

In fields where the growth curve has been fueled forward by warmer temperatures all summer, the black layer that signals the end of movement of starch into kernels may form earlier than normal. Smaller and fewer kernels may result. And although yields can still be respectable, heat and high nighttime temperatures may have stolen away those extra few bushels off the top.

Nanda, Indianapolis, is a crops consultant. Contact him at [email protected] or call 317-823-4250.

This article published in the October, 2010 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.

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