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Taking temperatures

Agriculture.com Staff 07/16/2009 @ 8:44am

Plants and people both fare best under normal temperatures. For humans, 98.6 degrees Fahrenheit. is optimal; corn fares best when its leaf canopy is 87 degrees Fahrenheit.

"That is when corn has optimum photosynthetic capacity," says Jeff Schussler, a Pioneer Hi-Bred research scientist. "A lot of physiological mechanisms peak at that temperature."

However, higher leaf temperatures, combined with limited soil moisture, lead to the telltale drought stress sign of leaf rolling. Abundant soil moisture can moderate a rise in leaf canopy temperature into the mid- to high-90 degrees Fahrenheit. level. Once plant canopy temperatures rise above 100 degrees Fahrenheit, though, serious physiological damage results, says Schussler.

"Once leaf temperatures get that hot, the stomates close and the plants can't take in carbon dioxide," he says. "Evaporative cooling in leaves shuts down, and leaf temperature continues to rise when cells break down and rupture. When cells break, you lose leaf area and yield potential."

Granted, you can't place a climate-controlled 87 degrees Fahrenheit. bubble over your field during a sultry July day. Still, you can discover how much your corn is heating up with an infrared thermometer (IRT). This tool reads the long-wave infrared radiation that crop canopies emit according to their temperatures. An IRT converts this to an electrical signal, which results in a temperature reading.

Irrigators can use the readings to help decide when to irrigate. Dryland farmers can't take any immediate action based on the readings. However, they can use the readings to compare which hybrids fare best under heat and drought.

"If a hybrid's canopy temperature tends to be 10 degrees Fahrenheit. cooler than others throughout the season, you may see higher yields at harvest," says Schussler. "This confirms that some hybrids can manage heat better than others."

The cost of an IRT is between $300 and $2,000, depending on the resolution. An IRT tends to work best in more western climates due to brighter sunshine and lower humidity.

Readings are taken when the corn has begun to canopy. "You want to take a reading at a time when there is bright sunlight to heat the surface of the leaves," says Schussler. "Avoid taking readings on overcast days."

An IRT can also be used on other crops. Wheat breeders in Mexico, for example, use the tool to breed drought-tolerant wheat, says Schussler.

Plants and people both fare best under normal temperatures. For humans, 98.6 degrees Fahrenheit. is optimal; corn fares best when its leaf canopy is 87 degrees Fahrenheit.

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