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a b s t r a c tWater scarcity is the most limiting factor in many irrigated areas of Mediterranean countries such as South Spain. Olive growing has been traditionally associated to rain-fed agriculture, although irrigation and practices related to intensive agriculture have been progressively introduced, requiring a more precise irrigation scheduling to save water. Thermal imaging is among the alternatives to assess the crop water status, especially when deficit irrigation (DI) strategies are applied. However, this technique requires of new advances to be more user friendly and robust for practical usage. The aims of this study were: i) to define threshold values of canopy temperature (T C ), Crop Water Stress Index (CWSI) and the temperature difference between canopy and the surrounding air ( T canopy-air ) for the assessment of the olive water status when a DI strategy is applied; ii) to define the best time of the day and the best area of the canopy to carry out thermal measurements, and iii) to obtain relationships between thermal indicators and main physiological parameters useful to estimate the crop water status from thermal data. The trial was conducted during 2015, in a hedgerow olive orchard (SW Spain) with 8-year-old trees (Olea europaea L., cv. Arbequina), under three irrigation regimes: a full-irrigation treatment (FI) and two regulated deficit irrigation treatments aimed to supplying 45% of the irrigation needs. In one of them, irrigation was scheduled from leaf turgor pressure related measurements (45RDI TP ). In the other, the crop coefficient approach was used to schedule irrigation (45RDI CC ). Significant correlations between Tc versus stem water potential (« st ) and leaf gas-exchange parameters (stomatal conductance to water vapour, g s ; net CO 2 assimilation, A N ; transpiration, E) were obtained (p ≤ 0.05), in particular from measurements taken at 10:30 GMT in the lower part of the sunlit side of the canopy. Moreover, the relationships between both T canopy-air and CWSI with the monitored physiological variables were very robust. We concluded that values of T canopy-air higher than 0 • C and values of CWSI up to 0.2 reliably reflect the plant water stress. Our results, therefore, suggest that both T canopy-air and CWSI measured at midday provide reliable information on the tree water status and are useful to schedule irrigation in hedgerow olive orchards, especially under DI 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 (Ψ 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 (ΔT), Ψ 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 Ψ 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.Spain / Prunus dulcis / canopy / temperature / infrared thermography / water requirements / soil water deficit Approche pour évaluer l'imagerie thermique infrarouge d'amandiers en conditions de stress hydrique.Résumé -Introduction. Optimiser l'utilisation de l'eau en agriculture implique de combiner des techniques physiologiques, technologiques et d'ingénierie, en particulier celles qui permettent de surveiller en permanence l'état hydrique de plantes soumises à un déficit d'irrigation. Une méthodologie pour estimer le stress hydrique de jeunes amandiers à partir d'images thermiques a été développée sur la base de l'évaluation de l'état physiologique d'arbres placés en conditions d'alimentation en eau limitée. Matériel et méthodes. Deux traitements d'irrigation ont été testés au cours de la période de demande evapotranspirative maximale (214e au 243e jour de l'année) dans un dispositif expérimental en verger d'amandiers [Prunus dulcis (Mill.) D.A. Webb., cv. Guara] : un traitement avec une irrigation déficitaire à basse fré-quence (LFDI), irrigué en fonction du statut hydrique des plants, et un traitement irrigué à 100 % de l'éva-potranspiration des cultures (C 100 ). La température quotidienne du couvert à midi (T C ) a été mesurée à l'aide d'une caméra infrarouge, ainsi que des mesures standards du potentiel hydrique de la tige (Ψ Stem ) et de la con...