Use of infrared thermography to assess spatial and temporal variability of stomatal conductance of grapevines under partial rootzone drying: an irrigation scheduling application

A thermal imaging technique to assess spatial and temporal stomatal conductance was studied in a field trial in Australia during the 2003-04 growing season. Images on the shaded side of the canopy were obtained using an infrared portable camera (Therma CAM PM575, FLIR Systems). "Dry" and "wet" leaves were used as reference surfaces to obtain temperature thresholds to eliminate non-leaf material temperatures in the analysis. An index (Ig) proportional to leaf conductance was obtained and compared with average stomatal conductance measured by gas exchange (Li-Cor 6400). Midday stem water potential, sap now and wetting patterns were also analysed to determine the effect of plant water status on reference temperatures. This technique could give a more accurate estimation of actual stomatal conductance of the whole canopy and canopy resistance of non-stressed grapevines, which could then be incorporated in the Penman-Monteith model to estimate evapotranspiration of deficit irrigated grapevines with variable canopy resistances.