Soil evaporation beneath and between olive trees in a non-Mediterranean climate under two contrasting irrigation regimes

Olive production with microirrigation systems has increased in the last 15 years in northwestern Argentina. An irrigation experiment in a commercial olive orchard was conducted from September 2005 to May 2007 under two different irrigation regimes (moderate irrigation MI, and high irrigation HI). From May 2006 to March 2007, soil evaporation was studied using microlysimeters located beneath olive trees, and spatial variability in a sunlit exposed area, and a shaded site was analyzed. The soil evaporation observed under the HI regime was higher than the equilibrium evaporation during the entire experimental period, while the soil evaporation under the MI regime was higher than the equilibrium evaporation only during end of autumn and winter. The high values of evaporation were associated with microadvection in the shaded area, but not in the sunlit sites between olive trees, based on the use of a microadvection coefficient. A model that takes into account the surface energy balance was used to estimate soil evaporation under the olive tree canopy. The first day after irrigation the model underestimated the observed values due to microadvection in the areas wetted by the drip emitters, whereas subsequent days (>1 day) the effect of microadvection was not present.