Crop Tattoos: Wearable Sensors Measure Plant Water Use

January 17, 2018 09:45 AM

Tattoos on crops? Absolutely. Want to know how much water a corn plant is guzzling or how fast a soybean plant is drinking? Stick on a tattoo and get an instant answer from a wearable plant sensor.

A remarkably promising sensor may provide farmers with actionable information on the real-time drinking habits of their crops. Applied in a simple, peel-and-stick adhesive fashion, a new graphene sensor measures leaf surface humidity, a function of how much water is transpired by crop plants. From on-the-go crop management to plant breeding, the innovative technology is layered with agricultural potential.

Iowa State University’s (ISU) Plant Sciences Institute (PSI), steered by Patrick Schnable, is composed of plant biologists, computational scientists and engineers. When PSI’s Liang Dong, associate professor of electrical and computer engineering, tackled the challenge of precision crop water measurement, he came up with a tiny, low-cost answer for a major issue.

Dong created an adhesive graphene sensor (which can be sized down to millimeters) sensitive to water vapor. The sensor measures how much water leaves the plant. Essentially, the sensor records how much and how fast a plant drinks.

The graphene within the sensor exhibits different levels of conductivity depending on the humidity. The conductivity of the sensor can be measured by running an electrical current across it. The changes of conductivity serve as a moisture gauge, according to Schnable: “It acts like a mercury thermometer. As the temperature goes up the mercury expands and goes up according to the corresponding temperature scale. The plant tattoo sensor reads water loss in a similar manner.”

A wire leads from the sensor to a small box located on the stalk or at the bottom of the plant. The box converts the electrical current to data. Schnable and Dong plan to experiment with different Wi-Fi methods to deliver data to the cloud.

External humidity levels don’t affect sensor performance, Dong notes: “For field applications, the sensor takes in local temperatures that will be fed to a readout circuit to eliminate any humidity effect on the sensor’s output.”

And dust? “The sensitive material of the sensor faces the leaf, and thus is physically protected by the tape from dust,” he adds.

Initial sensor use will involve plant breeders measuring drought tolerance in different crop varieties and hybrids. However, farmland is where Schnable sees the biggest sensor impact. “We’re excited because farmers are going to be able to use these to make water management decisions. For example, they could put sensors on a number of plants in a pivot circle. The information from the leaves would be transmitted to the data analyzer, which could then communicate with the pivot and tell it how much water to put in which parts of the field.”

Schnable emphasizes the multi-crop application of the sensor and its extremely fast set-up time. “We believe that this sensor can be used with virtually any crop. It is actionable information with which farmers can make decisions, but almost takes no time to get ready. Place the box and apply the sensor like adhesive tape; it’s that easy.”

A three-year, $472,363 grant from USDA’s Agriculture and Food Research Initiative (AFRI) “Miniature, Low-Cost, Field-Deployable Sensors To Advance High-Throughput Phenotyping For Water Use Dynamics” will enable initial field trials in 2018-2019 in Iowa and Nebraska. Michael Castellano, William T. Frankenberger professor of soil science and ISU agronomist, will direct the testing in collaboration with Dong and Schnable. The team hopes to commercialize the sensors by 2020. (ISU’s Research Foundation has applied for a sensor patent.)

"Our wearable plant sensor technology may become a game-changing approach to agricultural water management, and accelerate the process of breeding drought-tolerant crops,” Dong says.

“In the field, the challenge has always been how to figure out what plants are doing with water,” Schnable concludes. “Now, with sensor technology that goes on as simply as a tiny Band-Aid, farmers can know exactly how much water their crops are using.”

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