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Thirsty Crops Run A Temp

Kendall DeJonge’s mission is to take plants’ temperatures. But the crops, like corn, that he’s working with don’t have to open up and say, “ahh.” Instead, DeJonge employs an infrared radiometric thermometer (IRT). It is a simple point-and-detect temperature detection tool that you can own.

The USDA Agriculture Research Service (ARS) engineer is refining a simple way you can use IRT readings to pinpoint when a crop needs to be irrigated.

Creating a simple calculation

DeJonge is basing his work on research that confirms thirsty plants get hot. So a simple method of taking crop canopy temperatures could be a boon to farmers. Also, DeJonge points out, IRTs could be placed on posts in fields, center pivot irrigation systems, or even on a drone to gather temperature readings on crops.  

Scientists can interpret the IRT readings by using one of several indicators, including the commonly used crop water stress index (CWSI). 

Developed by ARS scientists in the early 1980s, the CWSI requires knowing air temperatures and humidity levels in addition to crop canopy temperature to calculate a vapor pressure deficit. Although accurate, CWSI is fairly technical to use.

DeJonge and his team of researchers have developed two new indices that are simpler to use than CWSI. These formulations include the degrees above nonstressed (DANS) index and the degrees above critical temperature (DACT) index.

The team is monitoring soil water levels and crop water use in fields fully to partially irrigated using IRT. They have found that DANS and DACT were just as effective as CWSI at determining water stress. 

Not only are both calculations simpler to employ, but also crop canopy temperatures need to be taken just once a day to be accurate. 

An online search found that an IRT with a handheld meter retails for between $600 and $700. Individual sensors that would be put on center pivots retail for $600 to $650.

DeJonge is now working on refining the calculations to establish water needs of specific crops under different scenarios. With his crop-water coefficient data, you could use handheld or drone-mounted IRTs to calculate water needs over extensive areas.

Find more details about DeJonge’s research at agresearchmag.ars.usda.gov/2015/aug/plants/.

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