Use of Aerial Thermal Imaging to Assess Water Status Variability in Hedgerow Olive Orchards

Characterization of the spatial variability in tree water status is a prerequisite to conduct precise irrigation management within an orchard. This study assessed the suitability of a crop water stress index (CWSI) derived from high-resolution aerial thermal imagery to estimate tree water status variability in super high density (SHD) olive orchards. The experiment was conducted at a commercial SHD olive orchard near Seville (southwestern Spain). The drip irrigated trees were submitted to three irrigation regimes (four plots per treatment): a full irrigation treatment replacing the crop water needs (ETc) and two regulated deficit irrigation treatments replacing ca. 45% of ETc. During the irrigation season, meteorological variables, soil moisture content, leaf water potential and leaf gas exchange measurements were performed. Infrared temperature sensors (IRTS) installed about 1 m above the canopies were used to derive the required baselines for CWSI calculation. A thermal camera installed on a mini RPAS (Remote Piloted Aerial System) allowed recording high-resolution thermal images at 5 representative dates of the olive tree growing season. CWSI values derived from aerial thermal imagery were sensitive to the deliberately imposed variations in tree water status within the SHD olive orchard. Maximum stomatal conductance and midday stem water potential showed tight correlations with CWSI. We conclude that high resolution thermal imagery captured from a mini RPAS has proven to be a suitable tool to capture tree water status variability within SHD olive orchards.