Grape growers are in need of improved precision irrigation management tools that are cost effective and low labor intensive to manage both irrigation amount and timing of their crops. Multiple experiments were carried out to find alternative methods to measure grape water stress that could be couple with water use estimates obtained from surface renewal stations. These methods ranged from using single point IRT temperature measurements to fully automated station that measured surface temperature in real time. The primary objective of this year’s experiments was to determine if stress indices derived from less labor intensive methods such using VSIM and IRT models could be used as a replacement to the more costly and labor intensive commonly used by growers at this time.
Experiments were carried out in three locations. Ten surface renewal stations measured grape water use and water stress in J. Lohr vineyards located in Paso Robles. Leaf water potential measurements were made along with single point IRT canopy temperature measurements using a handheld IRT sensor. Stress indices derived from the handheld IRT temperature values had inconsistent degrees of relationship strength from one site to the next, when compared to leaf water potential values. There was no single stress index, IRT or surface renewal derived, that performed consistently better than the others across all sites. Two stationary stations measured continuous canopy temperature measurements on J. Lohr sites 11-2 and 1-2. Micrometeorological data was collected from reference evapotranspiration stations set up nearby. Stress indices derived from these two stations had strong relationships with the leaf water potential values that were measured.
Two more stationary stations making continual IRT surface temperature measurements were set up in collaboration with Terlato Wine Group over vineyards in the Napa and Pope valleys. Micrometeorological data collected from nearby weather stations were used along with the IRT surface temperatures to calculate stress indices. These stress indices had strong relationships with leaf water potential measurements.
A weather station was set up in the UC Davis Tyree teaching vineyard equipped with sensors to measure canopy temperature, windspeed, air temperature, incoming solar radiation, and relative humidity. Sensible heat flux values calculated using IRT surface temperatures and the surface renewal method had a strong relationship with sensible heat flux values calculated from eddy covariance. Canopy stomatal conductance calculated using IRT canopy temperature measurements had a strong relationship with leaf stomatal conductance values measured with a porometer and stress indices also showed high correlation with leaf water potential measurements made on the Cabernet grape vines.