Iowa State research team seeking to spot crop stress from space

AMES, Iowa — NASA satellites can help decipher the difference between happy plants and unhappy plants, which could provide critical information to farmers.

A research team led by Iowa State University agronomy professor Brian Hornbuckle is studying how to use satellite-based sensors to remotely detect fields across the Corn Belt by estimating daily changes in plant water content and temperature, which could act as an early warning system for crop stress.

Courtesy Iowa State University

The three-year project funded by a $536,000 NASA grant will combine data from two of NASA’s orbiting observatories. The Soil Moisture Active Passive (SMAP) satellite detects microwave radiation emanating from earth, which is affected by the amount of water in soil and vegetation.

The ECOsystem Spaceborne Thermal Radiometer Experiment (ECOSTRESS) is aboard the International Space Station and measures plant temperatures using infrared radiation. Satellite readings will be validated in part by comparing them to on-the-ground measurements of water in corn growing on a research plot near Ames.

This is Hornbuckle’s ninth NASA grant.

"These satellites that NASA puts into orbit around the Earth look down on Earth, and we use these measurements to tell us about what's going on on Earth's surface, that we can make better decisions about how we use the resources on the earth," Hornbuckle said. "I've learned a lot about what goes into planning all these satellite missions, because normally, when you get funded by NASA, it's associated with one of these satellite missions."

The grant builds on prior experience that Hornbuckle has working with SMAP and a similar microwave-detecting satellite operated by the European Space Agency, Soil Moisture and Ocean Salinity (SMOS). Both SMOS and SMAP were designed to measure soil moisture, and researchers previously built models to filter out the signal from water held in plants.

But for this project, the filtering is flipped, said Hornbuckle, because they'll be looking at the water in the plants rather than the water in the soil.
"The twist on our work is that we're trying to use this SMAP satellite, that was originally designed to look at water in soil — and we're going to try to use it to also see water in plants," Hornbuckle said. "And we're going to test our hypothesis, which is that the water in plants can also tell us about whether or not they're happy."

Hornbuckle described "happy plants" as ones that can do photosynthesis. He said for this project, their hypothesis is that happy plants will have the most water inside of them in the morning.

"But during the day, because they're going to be doing photosynthesis, they're going to lose a little bit of water, and the water coming in through their roots won't be able to fill them back up again as quickly as they would like," Hornbuckle said. "That filling up will happen at night when the plants aren't doing photosynthesis anymore."

Their hypothesis is also that happy plants should look "really juicy" in the morning to the satellite, and they should look a little drier at night, he said.

"If they're unhappy, then what we think we're going to see is that the water in the plants will not change very much during the day, because they won't have been able to do any photosynthesis during the day because they didn't have enough water in the soil," he said.

If it's possible to decipher the water in plants, Hornbuckle said the data will be combined with satellite data which tracks the water in soil.

"Is there a way that we can put these two things together, to give us even better information about whether plants are happy or not, and whether or not they're able to do photosynthesis?" Hornbuckle said. "And whether or not they'll produce a lot of yield at the end of the year. Or, they are not happy because they don't have enough water in the soil, which means that they'll have less yield at the end of the year."

That kind of information would be valuable to producers, said Hornbuckle.

"In terms of the farmer, knowing whether or not plants are happy or not is going to help the farmer predict what their yield is going to be like at the end of the year," he said. "If they've had happy plants most of the summer, they should expect a very good yield. If the plants have been unhappy for a significant fraction of the summer, then they're going to take a yield hit."