Prospects of thermal imaging as a non-invasive tool to assess water status for irrigation scheduling in commercial vineyards

Aim: Irrigated viticulture is expanding worldwide mainly as a short-term adaptation strategy to climate change. Plant-based methods are increasingly being used for irrigation scheduling in commercial vineyards. Canopy temperature (TC) has long been recognized as an indicator of plant water status. TC_, but also the thermal stress indices, e.g. crop water stress index (CWSI) and stomatal conductance index (I_G) have been used to support and manage irrigation in several crops including grapevine. The goal of this work was to review thermal imaging as non-invasive tool to assess water status in commercial vineyards in Rioja (Spain) and in the wine regions of Douro and Alentejo (Portugal). 

Methods and Results: Thermal cameras were used as ground based portable sensors to manually assess water status. Significant correlations between T_C and/or thermal indices and stomatal conductance or stem water potential (Ψ_stem) were observed in the vineyards of these top wine regions. Recently, a thermal camera was also mounted in an all-terrain-vehicle for the on-the-go acquisition of thermal images. T_C, CWSI and I_G were significantly correlated to Ψ_stem at both canopy sides. Water status of a commercial Tempranillo vineyard was also evaluated using on-the-go thermal imagery retrieved from a moving quad at 5 km/h in Rioja. Moreover, an infrared radiometer was installed in an autonomous terrestrial robot to assess and map water status of commercial Touriga Nacional vineyard in the Douro Valley. 

Conclusions: 

Several trials carried out in Spain and Portugal showed the effectiveness of thermal imaging to monitor water status in commercial vineyards.

Significance and Impact of the Study: Our results are promising and show the potential of thermal imaging as a non-invasive technology in precision viticulture to evaluate vineyard water status, helping grape growers to optimize irrigation management.