Increasing agricultural demand for freshwater in the face of a changing
climate requires improved irrigation management to maximize resource
efficiency. Soil water deficits can significantly reduce plant growth
and development, directly impacting crop quantity and quality.
Dendrometers are a plant-based tool that have shown potential to improve
irrigation management in high-value woody perennial crops (e.g. trees
and vines). A dendrometer continuously measures small fluctuations in
stem diameter; this has been directly correlated to water stress. While
plant-based measures of water deficits are the best indication of water
stress, current dendrometers are imprecise due to mechanical hysteresis
and thermal expansion. The high-precision dendrometer created at the
OPEnS Lab alleviates these key failure points using zero-thermal
expansion carbon fiber, zero friction via a spring tensioning approach,
and a linear magnetic encoder. The device achieves 0.5-micron
resolution, and thermal fluctuations are less than 1 micron over diurnal
swings of 25°C. The cost of the device varies with build quantity; parts
are $200 - $450 each and assembly requires 6 to 12 hours per system.
Dendrometers are currently being deployed with telemetry based on LoRa,
which is under evaluation. Without solar charging and telemetry, the
battery is sufficient for over two years of operation. Mass deployment
of these automated dendrometers has the potential to provide a
continuous record of water stress driven changes in stems, providing
valuable decision support for irrigation management.