RED BLUFF, Calif. — For the last few years, University of California researchers have been promoting new devices called pressure bombs for determining an orchard’s water needs.
But rapid advances in technology have made the pressure bombs — which are also called pressure chambers — almost obsolete, a UC Cooperative Extension adviser said.
Tree monitors and weather gauges connected to online data systems and new advances in aerial imagery are alternatives that may gain popularity, said Allan Fulton, an irrigation and water resources adviser in the UCCE’s Red Bluff office.
“What we’ve been looking for are alternatives to the pressure chamber,” Fulton told walnut growers during a Jan. 20 workshop.
While relatively inexpensive, costing growers about $10 an acre, using pressure chambers can be labor-intensive, he said.
“You have to go to the orchard, and if you don’t get there you have no information,” Fulton said. “Also, it’s just a snapshot. ... I’ve always been encouraging growers to look for tools that will give you a continuous picture.”
Pressure chambers are like blood-pressure tests for tree leaves. UC-Davis has been using them to measure plant water stress since the early 1990s, but they became popular with growers in recent years as drought has led to drastic surface water restrictions.
About two years ago, the UC-Davis Fruit and Nut Center launched a website to help growers interpret their readings from the devices to determine how much water their trees need. The extension has weather stations positioned throughout the state to tell growers how hard their trees should normally be working to pull water under the temperature and humidity for that day.
Recently, private companies have introduced devices and systems to give farms an ongoing, automated report on their trees’ needs, and Fulton has been testing them for accuracy.
One such option is dendrometers, which are normally used to monitor the growth of trees but can also measure minute daily expansions and contractions of tree trunks to provide clues about water stress.
Another system developed by San Francisco-based startup Tule Technologies uses sensors installed above the crop canopy to tell growers how much water their plants are using and even when and how much to apply.
Finally, flyovers can give growers enhanced aerial images of their entire orchards and measure such things as temperature, Fulton said. Higher canopy temperatures are a sign of tree stress, he said.
“One of the values of the flyover system is it’s pretty good at troubleshooting problems in your irrigation system,” Fulton said.
“The pressure chamber is still a good tool, but there are some options now and it’s kind of exciting,” he said. “There’s a lot of good talent out there and I would expect these things to get better over time.”