Analysing the combined effect of wetted area and irrigation volume on olive tree transpiration using a SPAC model with a multi-compartment soil solution

Abstract

In this paper, we analyse the combined effect of wetted area and irrigation volume and its impact on olive tree transpiration (E p) after validating a multi-compartment SPAC model in a drip-irrigated hedgerow olive tree plantation. Modelled E p is compared with 2 years of calibrated sap flow records under two different irrigation treatments: a control (C) that was watered using a crop coefficient (K c) of 0.75 and a regulated deficit irrigation (RDI) in which applied irrigation was gradually reduced in relation to the K c of the control (50, 25 and 20% from June to August). The simulated midday leaf water potential (Ψ l) was also compared with measurements performed twice a month in each treatment and for both years. The model accurately predicted E p in both years for the two treatments (R 2 = 0.81 and RMSE = 0.29 mm/day), while midday Ψ l was slightly underestimated. Simulation analysis showed that (a) the use of drip irrigation systems always limits the maximum attainable E p for a given environment; and (b) irrigation design should depend on available water. If irrigation water is limited, the wetted area should be minimized to reduce losses from soil evaporation, thus maximizing the water devoted to E p; by contrast, if water is available, the maximum E p would be reached when wetting at least 30–40% of tree space. The model was accurate enough to capture the trends in E p and Ψ l of trees submitted to different irrigation regimes.