Corn gun removes some guesswork

The plants have no way of masking how they’ve been coping during this year’s dry season. In a matter of nanoseconds, the North Carolina State Extension corn specialist reads the canopy and outside temperature and is well on his way to determine in-season nitrogen applications.

The little gun in his hand lets him read the corn leaves like a book, and offers a precise glimpse into yield potential.

Thermal sensors have been used to schedule irrigation in the Southwest, as well as other applications. Heiniger and his colleagues in North Carolina are using the thermometers to make decisions on in-season nitrogen applications, taking their cues from the leaf and canopy temperature.

“We have found that we can use an instrument intended to measure water stress in a different way to measure nitrogen use in a plant,” he says. Researchers are also using chlorophyll meters to gauge nitrogen use during the season.

The key, Heiniger is finding, rests in the coolness of the canopy. Where water is a limiting factor, the leaf will be hotter, because the plant is not sweating. When the crop is under stress, it’s not using nitrogen. In effect, the plant shuts down.

The canopy temperature reflects the plant response to the environment as well as the health of the plant and how good of a root system it has, Heiniger says.

“Measuring the outside temperature and the canopy temperature can tell you how well the plant is doing at cooling itself,” he notes. “There’s a balance between the water going out of the plant and the gases coming in. That’s where we made the realization that the canopy temperature and the outside air can tell us whether or not the plant needs nitrogen.

In other words, when the corn is transpiring adequately, it’s getting enough water and nitrogen. “If it’s hotter on the outside than it is under the canopy, the plant won’t be doing a good job of transpiration.

“We were looking for a simpler way to make precision application of nitrogen,” Heiniger says. Instead of basing nitrogen applications on soil types, the decision is made based on the condition of the crop. “We found out that it just wasn’t soil type, but water holding capacity. From that we found we could measure how much nitrogen the corn needs by looking at color.”

At the Blackland Farm Managers Summer Tour at the Vernon James Research and Education Center in Plymouth, N.C., this past summer, Heiniger explained his promising research.

“We’ve got to get a better handle on nitrogen,” Heiniger said as Alan Mejer, a graduate student at North Carolina State University, points the $200-$300 Raynger MX thermal sensor at the crop. The sensors are now on the market.

“We have 71.8 degrees in the canopy,” the graduate student calls out. “82 degrees outside.” The sun moves from behind a cloud and both temperature readings increase. The gun also registers relative humidity.

In the first year of using the technology to determine in-season nitrogen applications, Heiniger has already shown differences between the canopy and the outside temperature on at least four dates. When the canopy temperature is higher than the outside temperature, the plant is suffering from stress and is not using nitrogen.

One year’s data suggest “we may have to look at pre-tassel nitrogen application,” Heiniger says.

Before using the thermal sensor, Heiniger would have to make an educated guess about in-season nitrogen application. “As with all guesses, nine times out of 10 you’re off a little bit. With this technology, we’re going to be able to control our rates and put on the most accurate applications of nitrogen that we can.”

Heiniger can almost guarantee this kind of technology will be used in North Carolina fields in the next few years. “We know the thermometers are sensitive,” he says. “We’re working on putting the numbers to be able to tell a farmer whether a 5 degree difference means the crop needs 50 pounds of nitrogen.”

“The ultimate application would be to mount a thermal sensor on a nitrogen applicator and let it control the nozzles as the tractor goes through the field,” Heiniger says.

Thermal sensors would give farmers in the field a tool to precisely gauge the potential of the crop during the growing season; the readings could quickly tell the farmer whether a cornfield was under stress.

“It may sound a little bit out in left field, but you can literally drive by a corn field at 55 mph and take a reading of the canopy and the outside temperature,” Heiniger says.

e-mail: [email protected]

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