Articles
THE DUAL CROP COEFFICIENT APPROACH: TESTING THE SIMDUALKC MODEL WITH PEACH ORCHARD EVAPOTRANSPIRATION EDDY COVARIANCE MEASUREMENTS
Article number
889_20
Pages
181 – 188
Language
English
Abstract
The SIMDualKc model is a water balance simulation model that allows estimating crop evapotranspiration using the dual crop coefficient approach.
This approach separately considers plant transpiration and soil evaporation through the basal crop coefficient and the evaporation coefficient, respectively.
The use of dual crop coefficients has proved to be more adequate than single crop coefficients for discontinuous crops, with incomplete cover of the soil, and for high frequency irrigation.
The model was tested with peach orchard evapotranspiration (ET) measurements obtained by the eddy covariance technique (EC). The measurements were performed in central Portugal under Mediterranean conditions, in a sandy soil, during two irrigation seasons.
Direct measurements of ET were thereafter correlated with continuous sap flow (SF) measurements (providing tree transpiration) and soil evaporation estimates (obtained from a locally calibrated model). These combination of techniques provided ET for the entire irrigation season.
The orchard had a low fraction of ground covered by vegetation which was taken into account in SIMDualKc by adopting a density factor for the calculation of the basal crop coefficient . Results showed a difference of up to 0.1 mm between mean daily measured (2.1 mm) and simulated (2.2 mm) ET. Thus the model slightly overestimated ET when comparing to ET obtained by way of a EC-SF relationship.
The experimentally determined single crop coefficient (Kc) was around 0.5, the same as the modelled Kc. Soil evaporation estimates by the SIMDualKc model were closer to experimental data than transpiration estimates.
The accuracy of the model is acceptably good considering the applications intended.
This approach separately considers plant transpiration and soil evaporation through the basal crop coefficient and the evaporation coefficient, respectively.
The use of dual crop coefficients has proved to be more adequate than single crop coefficients for discontinuous crops, with incomplete cover of the soil, and for high frequency irrigation.
The model was tested with peach orchard evapotranspiration (ET) measurements obtained by the eddy covariance technique (EC). The measurements were performed in central Portugal under Mediterranean conditions, in a sandy soil, during two irrigation seasons.
Direct measurements of ET were thereafter correlated with continuous sap flow (SF) measurements (providing tree transpiration) and soil evaporation estimates (obtained from a locally calibrated model). These combination of techniques provided ET for the entire irrigation season.
The orchard had a low fraction of ground covered by vegetation which was taken into account in SIMDualKc by adopting a density factor for the calculation of the basal crop coefficient . Results showed a difference of up to 0.1 mm between mean daily measured (2.1 mm) and simulated (2.2 mm) ET. Thus the model slightly overestimated ET when comparing to ET obtained by way of a EC-SF relationship.
The experimentally determined single crop coefficient (Kc) was around 0.5, the same as the modelled Kc. Soil evaporation estimates by the SIMDualKc model were closer to experimental data than transpiration estimates.
The accuracy of the model is acceptably good considering the applications intended.
Authors
T.A. Paço, R.D. Rosa, P. Paredes, G.C. Rodrigues, N. Conceição, M.I. Ferreira, L.S. Pereira
Keywords
irrigation scheduling, basal crop coefficient, soil evaporation, Prunus persica, discontinuous crops
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