Seasonal evolution of crop water stress index in grapevine varieties determined with high-resolution remote sensing thermal imagery

Abstract

The seasonal characterization of spatial variability in water requirements across and within vineyards could assist the viticulturist to fine-tune irrigation management for quality optimization. Remotely sensed crop water stress index (CWSI) is related to crop water status, but it is not known how applicable it is to different grape varieties at different times of the season. This study focused on the determination of the lower and upper baselines for calculating CWSI for the Chardonnay, Pinot-noir, Syrah and Tempranillo varieties at different phenological stages. Baselines were determined based on canopy temperatures measured with infrared temperature sensors placed on top of well-watered grapevines in 2011. Results indicated that non-water-stressed baselines differed depending on variety and phenological stage. During 2011, an aircraft equipped with a thermal camera flew over the vineyards on six particular days throughout the season at 150 m altitude above ground level. At the same time, leaf water potential (Ψ L) was measured for each variety. Variety and phenological stage affected the relationship between remotely sensed CWSI and Ψ L, with phenology having greater influence on the observed measurements than on variety. For instance, the one-to-one relationship between estimated and measured Ψ L had R 2 of 0.634 and 0.729 for variety and phenology, respectively. The baselines and estimations of Ψ L were validated in different vineyards of the same region and in a different season (2013) using the same methodology as in 2011. Data obtained in 2013 were in agreement with observations during 2011. It is concluded that the use of CWSI for assessing vineyard water status requires calibration to account for the effects, primarily of phenological stage, but also, of variety. Once calibrated, this can be successfully applied to other vineyards and seasons.