Evaluation of a simplified methodology to estimate the CWSI in olive orchards

The canopy temperature is a promising methodology for deficit irrigation scheduling. This measurement is used to calculate the crop water stress index (CWSI), which needs the estimation of non-water stress baseline (NWSB). In olive orchards, NWSB changed at different times of the day and throughout the season. The aim of this work was to evaluate a simplified methodology for estimating NWSB to allow reducing costs and facilitate the CWSI estimation. The experiment was performed during two consecutive seasons (2020 and 2021) in a young super-intensive density olive orchard (Olea europaea L. cv Manzanillo). Three irrigation treatments were evaluated in a completely randomized design with 6 repetitions: Control, Full Irrigated; Regulated Deficit Irrigation (RDI) with a period of water stress during pit hardening, and Rainfed. The midday stem water potential and leaf conductance were measured every week during the irrigation season. The canopy temperature was measured with a low-cost thermal camera attached to a tablet. The CWSI was estimated for the same trees used to measure the midday stem water potential and leaf conductance. The NWSB was calculated in different ways, considering several simplifications. Firstly, NWBS was obtained using previously published equations (one or several equations throughout the season). Secondly, climate data were measured in the orchard together with the canopy temperature or using daily values from a weather station nearby. CWSI estimations using different equations were closely related (R2 =0.95; MSE=0.008) and one fit was considered successful. Although the differences in the values from different sources was considerable and significant, the CWSI estimation did not present major variations and the use of data from the weather station could be assumed in commercial orchards. The CWSI successfully identified water stress in Rainfed conditions, mainly when the stomata closure was detected. However, the differentiation between Control and RDI was limited.