Wearable sensors have up to now been associated with monitoring medical conditions in humans. Now, the technology is being adopted to measure sap flow in crops to regulate water usage.
James Schnable, associate professor in the Department of Agronomy and Horticulture, and colleagues at Iowa State University are developing a Fitbit-like sensor to be worn by corn and other thick-stemmed crops. Funded by a Breakthrough Technologies award from the National Science Foundation, the researchers seek to measure rates of sap flow in real time, actual fields, and changing weather conditions.
The ability to precisely monitor sap flow could help researchers better understand how crops respond to drought conditions. That, in turn, would allow researchers to compare the drought resistance of different genetic lines with greater speed and accuracy, according to Schnable. This could lead to more water-efficient hybrids that can tolerate ever-harsher climates.
“There are different strategies plants can take and different strategies plant breeders can pursue depending on their goal, the environment they’re breeding for and the crop they’re working on,” said Schnable, associate professor of agronomy and horticulture, in a statement. “All of these, though, do require (that) you actually be able to look at how much water the plant is using, not over just an entire growing season but really on a day-by-day or hour-by-hour basis.”
Schnable emphasized the importance of understanding water use, given that a plant’s ability to resist drought competes with its ability to produce food. When a plant opens the tiny pores in its leaves to welcome the carbon dioxide essential for photosynthesis—and eventually, food—water escapes through those pores, making the plant susceptible to drought. Crops bred for higher yields invite in even more carbon dioxide, giving water more opportunities to depart.
Breeding crops for improved yields can be more effective with the knowledge of how different crop varieties begin or stop conserving water, according to the researchers. Pairing those observations with genetic analyses of the varieties could also offer provide details of the practical influence of various genes in the field, guiding modification efforts in the lab.
“The more we can actually measure some of those (individual factors) in the field and look at the differences between varieties, the more we can make precise judgments about how two different lines with the same level of drought tolerance got there,” Schnable said. “You could separate those (different factors) out and then breed for those individual factors separately.
SAP issues
The team’s project qualified for the Breakthrough Technologies program—which the National Science Foundation developed for “high-risk, high-reward” pursuits—in part because no one has managed to develop a sensor that can monitor sap flow over a full growing season in the field.
Iowa State’s Liang Dong crafted a bracelet-like device that administers small amounts of heat to the stem it fits around. Tiny sensors above and below the micro-heater will then record the amount of heat that passes by, effectively measuring how quickly the sap is carrying the heat away, and, by association, how fast the sap is flowing. The sensor’s nanoscopic structures and fibers should help prevent a loss of heat that could otherwise invalidate their readings.
The device’s flexibility comes by way of an elastic band that can stretch to accommodate the growth of corn stalks or other crop stems, including those of soybean and sorghum, that can widen substantially within weeks. The elasticity also enables device to monitor a stem’s diameter, which factors into the equations that describe how fast the heat is traveling and sap is flowing.
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