Monitoring of grapevine stem potentials with an embedded microtensiometer

Abstract

Context and purpose of the study – Vine water status is a crucial determinant of vine growth, productivity, fruit composition and terroir or wine style; therefore, regulating water stress is of great importance.  Since vine water status depends on both soil moisture and aerial environment and is very temporally dynamic, direct measurement of vine water potential is highly preferable.  Current methods only provide limited data. To regulate vine water status it is critical to monitor vine water status to be able to: (1) measure vine water status to predict the effect of water stress on the overall vineyard performance and fruit quality and optimize harvest management and wine-making  (2) properly regulate the water status to impose for a desired fruit quality or style (3) determine if water management has reached the desired stress level. 

Material and methods – We have developed a microchip microtensiometer sensor (5×5 mm) housed in a cylindrical probe that is connected to a datalogger or to a dedicated logger with wireless communication and power module.  The chip is a MEMS (microelectromechanical systems) microfluidic device with the same measurement principle as the classic soil tensiometer, but it operates over a range of more than 50 bars. The sensor is embedded into the trunk of vines and continuously monitors stem water potential. With the wireless logging, real-time monitoring of stem potentials is available online. Testing in field grown grapevines has been done over several years and compared well to pressure chamber measurements of stem potential.

Results – Field tests with embedded sensor probes in vineyards demonstrated continuous measurements over several months under a range of weather and water stress levels.  Pressure chamber readings of stem potential in the monitored vines were well correlated to the sensor output. Though a sensor installation is recommended for one growing season, multiple years of measurement have been found.  Results have been most consistent with diffuse porous woody species with very small vessels. Sources of variability in the success of the sensor in grape stems are not clear, but appears to relate to the inherent variability in grape stems and possibly to embolisms of very large vessels. A sensor version with a much smaller installation hole for young vines and small stems has been developed and is being tested with promising results.  This precision data on plant water stress will support precision water management, and will support new understanding of plant responses to water and environment.  The microtensiometer sensors are available commercially by FloraPulse Co.