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Save Water by Measuring Temp of Plants

For farmers in places like Colorado, where population growth and drought have made water a critical issue, managing irrigation water more effectively has emerged as a top priority.

“With water becoming more precious, we need to exploit the potential of every tool available,” says Kendall DeJonge, an Agricultural Research Service engineer in Fort Collins, Colorado. “Using an infrared radiometric thermometer (IRT) to determine a crop’s water needs just makes sense.”

Currently in research applications, IRTs are placed on field posts or center pivot irrigation systems. Temperature readings are gathered hourly or daily on crops. Scientists then interpret the data by using one of several indices, including the crop water stress index (CWSI), which is considered the gold standard for quanti fying water stress. Developed in the early 1980s, the CWSI also requires that users know air temperatures and humidity levels.

Because the CWSI method is fairly technical and requires additional measurements, many farmers will guesstimate when to irrigate, which could mean water is wasted by overirrigating. As a result, yields will suffer because crops aren’t getting enough to drink. What farmers need is a simple, yet effective, method to monitor the water demands of a crop.

Simplified process
That’s where DeJonge comes in. The scientist has found a way to simplify the process by using canopy temperatures to determine if crops are water stressed.

His research centers around IRTs, affordable sensors that can determine the crop canopy temperature and whether a crop is water stressed.

He and his colleagues compared the CWSI with five other formulas for interpreting IRT data to see how well they could detect crop water stress over two years in a corn-sunflower rotation. All of the indices used crop canopy temperatures to determine water stress levels.

The team developed two indices for the study, which are simpler than CWSI. The Degrees Above Non-Stressed (DANS) index is calculated by comparing a stressed plant’s temperature with the temperature of a nonstressed plant in the same environment. The second study, Degrees Above Critical Temperature (DACT), is based on an established crop temperature threshold, with plant water stress determined by how many degrees above that threshold the plant temperature reaches.

Crop canopy temperatures for DANS and DACT were taken each day at 2 p.m., when water stress levels were usually highest. Researchers monitored soil water levels and crop water use. They fully irrigated part of the field, while intentionally stressing other areas.

Even though they require much simpler measurements, the findings show the DANS and DACT indices are just as effective as CWSI.

DeJonge plans to develop crop water coefficients that establish water needs of specific crops under different scenarios. With that data, IRTs could soon be widely used by farmers. He also foresees farmers using handheld IRTs in the not-so-distant future and eventually using the thermometers with drones to calculate water needs over extensive areas.

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