Infrared temperature sensors for automated monitoring of orchard tree water status

Accurately assessing tree water status is important in optimizing crop water use, particularly when employing conservation strategies such as regulated deficit irrigation (RDI). We previously found that RDI could improve fruit quality and reduce trunk injury in mechanically harvested tart cherry, but orchard managers have been reluctant to use this approach without better techniques to monitor tree water status. Stem water potential has been the most reliable method for determining water status of fruit trees, but this technique is time consuming and requires specialized equipment and training. Direct measurement of the leaf to air temperature difference has the potential to indicate plant water status, and can be used in a remote automated system. We made automated measurements of the canopy-to-air temperature difference using infra-red sensors and compared them to stem water potential measurements in tart cherry trees over two seasons. The canopy-to-air temperature difference was well correlated with stem water potential, but the correlation changed over the season, perhaps due to leaf age or crop load. Refinements are needed for this approach to be commercially useful.