Measuring and Modelling Soil Evaporation in an Irrigated Olive Orchard to Improve Water Management

The aim of this study was to estimate soil evaporation (Es) in an intensive olive orchard. Measurements of Es were performed for 19 days using microlysimeters, during summers 2010, 2011 and 2012 in southeast Portugal. In order to relate each area type to radiation transmissivity, ground cover measurements were performed over the years. These data were used to calibrate and validate an empirical model for Es estimation. Measured daily average Es was 0.55 +/- 0.14 mm; the model estimated 0.53 +/- 0.18 mm for the same days, with a determination coefficient of 0.94. This corresponds to 9% of the reference evapotranspiration, representing well the overall values estimated for the summer, except for days after rain. Regarding the wet area, measured Es for the validation data set was 2.42 L/(m(2) of wet area), the estimated was 2.49 L/(m(2) of wet area). Measured average Es in dry area (validation data set) was 0.42 L/(m(2) of dry area), estimated Es was 0.43 L/(m(2) of dry area). The large exposed dry area had a significant contribution to evaporation. On average, estimated Es during a typical Mediterranean summer was 10% of reference evapotranspiration, representing 30% of transpiration and 23% of evapotranspiration.