Decoupling factor, aerodynamic and canopy conductances of a hedgerow olive orchard under Mediterranean climate

The degree of coupling between canopy and atmosphere, through the decoupling factor Ω , well describe the behaviour of a crop with respect to its water use and carbon dioxide exchange. Super high density hedgerow olive orchard system is in great expansion all over the world and, since it has a complex field structure in rows of adjacent trees, investigations are necessary to assess the Ω patterns, as well as aerodynamic ( g a ) and canopy ( g c ) conductances in different water conditions. In this study, in a hedgerow olive orchard (cv. “Arbosana”) submitted to full (FI) and regulated deficit irrigation (RDI), cropped under Mediterranean semi-arid climate (southern Italy), Ω has been determined using g c , as deduced by inverting the Penman-Monteith equation, and g a , by upscaling the wind speed measured in a close station to the canopy; the transpiration has been measured by sap flow thermal dissipation method. The results showed that this olive orchard results very well coupled to the atmosphere, in any soil water conditions; Ω is generally very low, being equal in mean to 0.015 ± 0.008 and 0.019 ± 0.012 for FI and RDI, respectively. This condition is linked to g a and g c values; in fact, canopy conductance is much smaller than the aerodynamic one in any water and climatic conditions, except when all canopy surfaces are saturated in water. In this latter case, the g c assumes highest values due to the contribution of the part of conductance attributable to the structure of the orchard.