MEASUREMENTS AND ESTIMATES OF PEACH ORCHARD EVAPOTRANSPIRATION IN MEDITERRANEAN CONDITIONS

Abstract

In some south Europe regions with Mediterranean climate, orchards have to be regarded as sparse crops, even though they are considered as intensive agriculture from an economic point of view. Previous studies showed some discrepancies between crop coefficients tabled in FAO Irrigation and Drainage Paper 56 and the observed values for such orchards. There was a need for an intensive study regarding these differences. The evapotranspiration (ET) of a peach orchard (5x2 m plant spacing and crop ground cover of 29%) was studied in central Portugal, during two irrigation seasons. ET was directly measured with the eddy covariance technique. Simultaneously, sap flow (heat dissipation, Granier method) and soil evaporation (microlysimeters) were measured. When scaled up to the stand level, the sap flow data were strongly correlated with the ET data (after deduction for soil evaporation) but showed an underestimation of transpiration. A regression was used to estimate ET from the sap flow data. This approach allowed the use of the continuous records of sap flow to estimate ET for the whole season, at low cost and with good reliability. Mean evapotranspiration was about 2 mm/day, mean measured soil evaporation was around 10% of ET and mean measured crop coefficient was close to 0.5, for the considered periods. Mean measured crop coefficients were lower than crop coefficients estimated with the FAO Paper 56 approach, which yielded ET mean estimates over 35% higher than the measured ET. At the farm level, irrigation efficiency was found to be lower than expected for a drip irrigation system (50 to 70%).