The Canopy Temperature Response to Vapor Pressure Deficit of Grapevine cv. Semillon and Razaki

The main objective of this study was to determine canopy-air temperature differential, which can be used to quantify crop water stress index (CWSI) for grapevine (Vitis vinifera L.) grown with drip irrigation during the spring cultivation period of 2005. Specifically, crop response to water loss, atmospheric temperature and air vapor pressure deficit (VPD) in the soil–plant–atmosphere continuum were examined to detect crop water stress. The effects of three irrigation programs (when depleted 30, 50 and 70% of the available water holding capacity within 0.90 m soil profile depth) on two grape cultivar (semillon and razaki) yields, and resulting CWSI were investigated. The non–irrigation treatment (NI) was also used for determination of fully stressed baseline. The lower (non-stressed) and upper (stressed) baselines were determined from measurements of canopy temperatures, ambient air temperatures and vapor pressure deficit values and the CWSI was calculated with three irrigation levels using the empirical approach. The CWSI value was useful for evaluating crop water stress in grapevine and should be useful for timing irrigation and predicting yield.