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

Abstract

The degree of coupling between canopy and atmosphere, through the decoupling factor Ω, well describes the behaviour of a crop concerning 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 (ga) and canopy (gc) 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 a Mediterranean semi-arid climate (southern Italy), Ω has been determined using gc, as deduced by inverting the Penman-Monteith equation, and ga, 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 during daytime equal in mean to 0.021±0.003 ms-1 and 0.018±0.004 ms-1 for RDI and FI, respectively. This condition is linked to ga and gc 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 gc assumes the highest values due to the contribution of the part of conductance attributable to the structure of the orchard.