The aim of this work was to evaluate, for an olive orchard in the Aljarafe county, the method developed by Orgaz et al.

AbstraetMeasurements of leaf water potential ('I') and stomatal conductance to H 2 0 (g) were made in 26-year-old Manzanillo olive trees under irrigation and dry-farming conditions. On days of high water demand, the olive trees reduced water losses by closing the stomata, so preventing excessive water stress. The analysis of g values versus photosynthetically active radiation (IPAR) and vapour pressure deficit (VPD), showed that stomata were fully opened at relatively low IpARlevels, from about 500 Jlmol m-2 S-l.Also, g decreased with increasing VPD, for values of up to approximately 4 kPa. After plotting the relative extraetable soil water (REW) values against their counterparts of pre-dawn leaf water potential ('I'pd) , it was observed that 'I'pd remained eonstant for values ofREW higher than 0.4, with a mean value of -0.46 MPa.

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