Severe droughts have devastating ramifications. They destroy crops, sometimes leading to food shortages and price hikes. They also can put a financial strain on farmers, who pay for more water to irrigate their fields. To help lessen a drought’s effects, Member Liang Dong has developed sensors he calls plant tattoos. They can estimate how well various crops retain water during a shortage.
The tiny sensors—a few hundred micrometers in diameter—are made of multiple layers of graphene-oxide, arranged in a pattern of dark circles and dots that gives them the appearance of tattoos. The unique pattern determines the device’s electrical properties—a proprietary design that Dong developed for the application. It is stuck to the underside of a plant’s leaf with adhesive tape.
Thanks to graphene’s ability to sense moisture, it can help farmers determine whether one variety of, say, corn will last longer in a drought than another depending on how well it absorbs and retains water from the soil. Such information can help farmers select which vegetable or fruit variety is most likely to survive in their fields.
Dong is leading the team at Iowa State University, in Ames, where he is associate professor of electrical engineering and faculty scholar at the school’s Plant Sciences Institute. The group includes plant scientists and Ph.D. students.
“We have wearables for people to measure their heartbeat, steps, and calories burned. So why not for plants too?” Dong says. “There is a significant need to use sensors for crops.”
A SMARTER WAY
The usual method of determining how much water a plant absorbs and retains involves uprooting the plant from the field and carrying it to a laboratory. Measurements can take a few days, according to Dong. And it’s expensive. The plant tattoo, however, collects information continuously and more effectively, he says, and it costs less than US $1.
Two thin wires connected to the tattoo are run to a button-cell battery and a simple readout circuit that measures electrical current. If the current exhibits a decrease, the elapsed time indicates water moving from the plant’s roots to the leaf where the sensor is. The changes in current are sent to an app via Bluetooth.
The sensors also can be applied to monitor water retention by measuring when plants are releasing water from their leaves, and thus determine which are better at conserving water.
Dong and his team tested the sensor on two different types of corn. The two differed markedly in how fast they absorbed water. In one type, it took an average of 80 minutes for water to travel from the fourth to the ninth leaf; the other type did the same in an average of 28 minutes, according a research paper Dong published in last November’s issue of Advanced Materials Technologies. Corn that moves water up faster is likely to do better in a drought, he says.
BETTING THE FARM
Monitoring water absorption and retention is really just the start for his device, he says. The next steps are to measure a plant’s nutrition levels, oxygen, pesticide levels, and more.
And Dong’s team is working to develop new sensors to measure fertilizer in soil. He and three colleagues founded a startup, EnGeniousAg, to design, manufacture, and sell the sensors, which also could be applied in greenhouses and indoor farms relying on artificial light.
This article is part of our April 2018 special issue on agtech.