Approach to assess infrared thermal imaging of almond trees under water-stress conditions

Introduction. Optimising agricultural water use implies the combination of physiological, technological and engineering techniques, especially those for continuously monitoring the water status of plants subjected to deficit irrigation. A methodology to estimate water stress of young almond trees from thermal images was developed based on assessing the physiological status of almond crops under limited water-supply conditions. Materials and methods. Two irrigation treatments were tested during the maximum evapotranspirative demand period (214th to the 243rd day of the year) in an experimental almond [Prunus dulcis (Mill) D. A. Webb, cv. Guara] orchard: a low-frequency deficit irrigation (LFDI) treatment, irrigated according to the plant-water status, and a fully irrigated treatment (C-100) at 100% of crop evapotranspiration. Daily canopy temperature at midday (T-C) was measured with an infrared camera, together with standard measurements of stem-water potential (Psi(Stem)) and stomatal conductance (g(S)). The time course of these parameters and their relationships were analysed. Results and discussion. The time course of the parameters studied showed highly significant correlations among the differentials of canopy-air temperature (Delta T), Psi(Stem) and g(S). The methodological protocol for analysing thermal images allowed a time saving in processing information and additionally offered the possibility of estimating the Psi(Stem) and g(S) values. Conclusion. Our results confirm that infrared thermography is a suitable technique for assessing the crop-water status and can be used as an important step towards automated plant-water stress management in almond orchards.