Issue link: https://www.e-digitaleditions.com/i/1413164
What is a dendrometer? A dendrometer measures the growth of a plant, such as its trunk, branch or fruit, over time. In their simplest and oldest form, a dendrometer can be a tape measure or band wrapped around a tree trunk that is read regularly, such as monthly or annually. Today's dendrometers are much more sophisticated, using an automated meter connected to a data logger. Parra uses what is known as a point dendrometer, which measures a single surface area of a tree trunk. The device consists of two shafts, one that is drilled into the tree for mounting and a second that is tightly placed against the trunk. This second shaft connects to a linear voltage displacement transducer (LVDT), which records the expansion and contraction of the trunk. These changes can provide insight into the real-time plant-water status of a tree, with continuous measurements typically showing contraction during the day and expansion at night. The need for irrigation is signaled when contraction is observed at night, which is generally considered an indicator of stress. "We've gotten really good at watching and monitoring our nutrition and water and I think there's still room for improvement," Parra said. "For us, it really comes down to having good data to work off of so we can make micro-adjustments that over the long run deliver savings. For me, the value is having the plant-based data – something literally measuring the tree." Adjusting to optimize dendrometer data To maximize water use efficiency (and prior to the installation of dendrometers), Parra added a dual irrigation system on his newly planted orchards. This design affords him the ability to tailor his irrigation and fertility program to specific varieties within an orchard block. "We have a block that is 50% Nonpareil and 50% Monterey, and we can control the irrigation exclusively by variety," Parra said. "It's a really good tool, especially around harvest when we go to dry down our Nonpareils – we don't stress our Montereys. I just crack one valve and I can water all my Montereys while I deficit irrigate my Nonpareils. It's a big deal." The ability and flexibility to irrigate by variety also comes in handy during the growing season, especially when data is factored in from Parra's dendrometers. If one variety in a block shows some mild stress while another doesn't, he can strategically and precisely place water where it's needed. "This comes down to saving water because it's not necessary to get WATER USE Continued from page 2 "The tree got what it needed, when it needed it, as opposed to trying to fill the glass." — Sal Parra, Jr. 3