The effects of water stress on evapotranspiration and leaf temperatures of two olive (Olea europaea L.) cultivars

The evapotranspiration (ET) and leaf temperatures of two olive (Olea europaea L.) cultivars 'Ayvalik' and 'Gemlik' were studied comparatively in fully-irrigated and water-stressed plants. The pot experiment was conducted under field conditions in 2009 and 2010. The experiment consisted of 4 treatments: 1) non water-stressed, 2) mild water-stressed, 3) moderate water-stressed, and 4) fully water-stressed. Leaf temperature (Tc) and ambient air temperature (Ta) of each seedling were measured at midday with an infrared thermometer and psychrometer respectively, and Tc-Ta was assessed. It was found that the irrigation water requirement of 'Gemlik' olive seedlings exceeded that of 'Ayvalik' olive seedlings. Tc-Ta was highest in the fully water-stressed treatment and lowest in the non water-stressed treatment for both olive cultivars. In all treatments, the Tc-Ta of 'Gemlik' was higher than that of 'Ayvalik'. The relationship between Tc-Ta and ET was linear and the coefficients of determination (R-2 = 0,72-0.74 for 'Ayvalik', R-2 = 0.62-0.72 for 'Gemlik' according to the analysis of linear regression) were statistically significant at p < 0.001 for both cultivars. The study showed that leaf temperature changed depending on ET in both olive cultivars and that an infrared thermometer can be used for measuring daily ET in olive seedlings.