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James Schnable stands between rows of corn in the field Craig Chandler, University Communication
DROUGHT RESPONSE: By measuring the water use of plants through a stretchable sensor, James Schnable hopes to better understand how crops respond to different kinds of drought.

'Wearable' crop water sensors put to test in Nebraska

A sensor mounted on a cornstalk uses movement of heat up and down the stalk to determine crop water use.

It's been called a kind of "Fitbit" for corn. Sure, corn plants don't have a heart rate to monitor, but they do take up and transpire water.

That's what James Schnable, associate professor at the University of Nebraska-Lincoln's Department of Agronomy and Horticulture, hopes to measure with a new kind of "wearable" sensor mounted on corn plants.

Schnable, who is developing the sensor with the help of colleagues at Iowa State University, notes the sensor — designed with a malleable material inside a stretchable band — measures the movement of heat up and down the plant's stalk. The sensor uses that heat measurement to estimate how much water is moving through the stalk.

"One of the really cool innovations my colleague Liang Dong at Iowa State came up with is putting a stretch sensor in that elastic," Schnable explains. "That means you're not constraining the growth of the corn plant as it grows, but it also is measuring how much it's stretching, so we can continue to measure the diameter over time."

Schnable says this provides a more direct measurement of water use compared with soil moisture probes, which often are used by growers and researchers alike to measure crop water use indirectly by measuring how much moisture is available in the soil profile.

"The nice thing is if you have this band on the plant, you're measuring how fast the plant is running through that supply of water," Schnable says. "The analogy I use is if you're trying to figure out if you can afford to take a new job with a certain salary, you could take a snapshot of your bank account, but really what you want to know is, 'What's my burn rate in a week or in a month?' We're going from measuring how much is in the bank to measuring the burn rate of different parts of a cornfield."

"That's exciting to me as a biologist, because I can look at different varieties of corn, how they respond to different environmental changes," he adds. "It's also exciting as an agronomist, because if you're somewhere out in central or western Nebraska with a big variable-rate center pivot, this gives you better data than just looking at how much water is in the soil, but how fast are plants in different parts of your field burning through their reserves of water."

There are a couple of potential benefits to growers, Schnable says. First, the technology likely will be scalable enough, and available at a low enough cost, to provide a sensor for on-farm use. In this case, farmers could monitor crop water use across an area of a field to make irrigation decisions.

In the longer term, he says, he hopes to help gain a better understanding of why different varieties respond to different kinds of drought in different ways.

"The most basic example of this is if a plant is in a terminal drought, its best strategy is to hurry up, flower, make some grain, so you get some yield instead of nothing," Schnable says. "If a plant is in a temporary drought, its best strategy is to shut down, conserve water and wait for the rain to come back, and you get a lot more yield than if you panic and flower too early. If you just do an end-of-season drought stress yield comparison between a drought-stressed and well-watered variety, sometimes one will win, and sometimes the other will win. But you're not really getting into the details of why one won, and why a different one won in a different kind of drought."

Schnable notes he and colleagues at UNL and ISU currently are validating the sensor's capabilities using beta models in the field. However, their goal is to start using the sensors in UNL's Greenhouse Innovation Campus in Lincoln this winter.

"In the greenhouse, we have another way of measuring the same thing," he says. "Because the challenge is if you design a sensor to measure something nobody's measured before, how do you know if the data you're getting has any meaning at all? In a greenhouse, you can measure water use by weighing the pot, and as the plant uses water, the weight will decrease."

If the sensors work as intended in the greenhouse this winter, Schnable says they will be used in yield plots at various locations in Nebraska next year.

"Depending on the year, finding where you're going to get the right level of drought is challenging," he says. "In Nebraska, we're fortunate to have access to fields all across the state. Usually, somewhere in the state, there will be that band where we'll get the right kind of biologically interesting drought."

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