Development of economical wifi-connected open-source sap flux probes
Author: Stephen Good, Chet Udell, Nik Wiman
Published: 2021
Summary: In order to maximize orchard productivity while minimizing costs, tree fruit producers require accurate information about tree water use, particularly crop transpiration rates. The most direct way to measure orchard-level water use is through sap flux probes, which are inserted into the trunks or stems of trees to monitor the vertical flow of water. These sap flux probe systems can provide direct estimates of the water passing through the stem/trunk of individual plants. In this project, we have developed an economical, open-source sap flux measurement package in collaboration with the Openly Published Environmental Sensing Laboratory (OPEnS Lab: http://www.open-sensing.org) at Oregon State University, which is devoted to developing similar low-cost ‘internet of agriculture’ technology solutions. Our design makes use of the commonly used Adafruit M0 LoRa Feather Microcontroller as well as other economically available electronic components, all of which are install onto three custom printed circuit boards. The OPEnS sap flux system can be built with $302 worth of components. Tests of the OPEnS probes against commercially available probes demonstrated accuracy at the 15-minute (r2=0.82) and daily (r2=.90) timescales. Results at the daily timescale for a test on a Cherry tree in fall 2020 are shown below. It is expected that as a result of this proposal we will make available to tree fruit growers in the Pacific Northwest, and elsewhere, an alternative method for monitoring orchard water use that commercial growers can implement economically and effectively. The final objective of this project is the publication of a technical publication, with an associated design and operating files, that describes how to build, install, and operate a sap flux monitoring network with little prior experience in electronics or computer programing.
