Use of thermography and leaf relative water content to estimate water status in young olive trees

The measurement of plant water potential by pressure chamber is currently the most widely used and reliable method to estimate plant water status. However, this practice is destructive and requires a big amount of time to get a representative measure of orchard water status. For this reason, finding new systems to estimate plant water status is critical for precision irrigation protocols. The aim of this study was to test leaf relative water content (RWC, %) and thermography techniques as potential indicators of plant water status to provide accurate alternative methods to estimate water status in olive. To achieve this purpose, leaf water potential (Ψleaf), RWC and thermal images were obtained from plants grown in growth chambers under different hydration conditions: from full hydration to very severe stress. Ψleaf, RWC, and crop water stress index (CWSI) were correlated to develop a model. Ψleaf was measured with a pressure chamber; RWC was determined in the laboratory from leaf fresh, turgid and dry weights; single-leaf thermal images were acquired using a hand-held thermal camera. A strong direct relationship was found between Ψleaf and RWC (R2=0.71). An inverse relationship between Ψleaf and CWSI was also found (R2=0.61), for Ψleaf values below -1 MPa. On the other hand, a weaker relationship between RWC and CWSI was detected (R2=0.33). Olive plant water status could be estimated more reliably with a multiple linear regression model combining RWC and CWSI data (R2=0.76). Further on-field studies will be needed to confirm these results and chiefly the importance of using RWC in the model to assess olive tree water status.