A model of daily mean canopy conductance for calculating transpiration of olive canopies

Abstract

We tested the hypothesis that the transpiration (λEp) of high-coupled canopies, such as olive groves, may be calculated on a daily basis with sufficient precision by the Penman–Monteith ‘big leaf’ equation, by a model of bulk daily canopy conductance (gc) capable of scaling for canopy dimension. Given the limited data required, such a model could replace the standard approach (ET0 × Kc) for calculating olive water requirements, enhancing the precision of estimates. We developed a specific model of daily gc for unstressed olive canopies that was calibrated by transpiration measurements obtained by water balance from a 2-year experiment in a mature orchard with λEp ranging from 0.6 (February 1993) to 11.5 (July 1994) MJ m–2 day–1 and where leaf area index (L) changed from 1.25 to 2.5. The model uses the intercepted fraction of daily PAR and a linear function of average daytime temperature. The model was validated with λEp data collected by eddy covariance in a 3-year experiment conducted in a growing orchard that differed in L and cultivar from the one used in the calibration. The gc model, when used in the Penman–Monteith equation, gave very good daily λEp predictions for all seasons during 3 years, ranging from 0.5 (November 1998) to 5.5 (June 2000) MJ m–2 day–1, indicating that the goals of dealing with the dependence of olive gc on L and of simulating the seasonal variations in gc were achieved. A comparison with the Jarvis gc model, calibrated with 2 months of measured gc hourly data, showed that the gc model developed here performed better than the Jarvis model for the 3-year dataset. The exception to this was the period in which the Jarvis model was calibrated. This indicates that (1) the Jarvis model did not account for the seasonal variations in gc of the olive trees; and (2) the spatial and temporal scale assumptions required in the calibration of gc generate seasonal errors in the simulated bulk daily λEp for this crop. The applicability of this bulk gc model is restricted to well watered olive canopies and to the one-layer approach of calculating λEp but it could be adapted to rain-fed canopies in the future.

Performance assessment of AquaCrop model for estimating evapotranspiration, soil water content and grain yield of winter wheat in Tensift Al Haouz (Morocco): Application to irrigation management

“…The same observations have been reported during the calibration stage (see the previous section). Indeed, the AquaCrop adopts the FAO-56 dual approach (Allen et al, 1998) for calculating ET cact and this approach has generated much criticism when applied in the semi-arid Mediterranean region (e.g., Testi et al, 2004;Katerji and Rana, 2006;Lovelli et al, 2007;Orgaz et al, 2007;Er-Raki et al, 2007, 2009, 2010c as reported by Katerji et al (2013).…”

Influence of different irrigation regimes on crop yield and water use efficiency of olive

“…The amount of PAR intercepted by the canopy of olive tree was estimated by the model of PAR interception, initially developed by Mariscal et al (2000c) and later modified by Orgaz et al (2007).…”

Seasonal dynamics and operational monitoring of hedgerow olive tree transpiration in response to applied water

“…With data from year 2011, we calibrated the Orgaz gc equation (Orgaz et al, 2007) to our olive orchard conditions, to obtain the following gc equation (mm s -1 ) for our olive orchard:…”

“…Transpiration of olive trees is mainly controlled by canopy conductance, as derived with the model of Orgaz et al (2007). Nevertheless, the main challenge in such models remains the integration of the effect of water stress.…”

“…In this study, we hypothesized that directly relating readily available VI of wellwatered olive trees to ground-based plant water-stress indicators might provide indirect assessment of the actual transpiration and water requirements of olive orchards. In this context, the objectives of this paper were: (1) to determine the transpiration dynamics and related crop transpiration coefficients of a hedgerow olive orchard in southern Portugal during the course of the summer under two (well-watered and moderate) irrigation regimes, (2) to validate whether treatment A-derived Kcb is from a well-watered treatment, by comparing field-derived sap-flow ETc values to ETc values obtained with the Penman-Monteith (PM) model incorporating values from the Orgaz et al (2007) daily mean conductance (gc) model, (3) to analyze the dynamics and derive Kcb-SAVI and Ks-ψst relationships, and (4) to assess the feasibility of integrating those relationships into the FAO56 model, and of using SAVI and ψst measurements as inputs to monitor hedgerow olive tree transpiration in southern Alentejo.…”