Abstract
The study of crop water conditions is increasingly based on plant responses to combinations of soil moisture and atmospheric evaporative demand. Several indicators can now be used to estimate this response at relatively low cost, making this integrated approach promising for scheduling irrigation in valuable crop plantations, such as fruit trees. Irrigation effects on plant water potential and leaf conductance were studied on mature olive trees of cultivars Frantoio and Leccino, grown in field conditions near Benevento (southern Italy) and submitted to different watering regimes from pit hardening to fruit veraison. Leaf conductance responded diurnally and seasonally to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. It decreased with increasing vapour pressure deficit during the season and diminishing water potential. Results suggest that, in addition to whole plant physiological factors and environmental conditions, there are endogenous inputs influencing leaf level water relations. Olive trees are long established to be efficient users of soil water, although more information on maintenance of assimilation and transpiration during drought may help in planning improved regulated deficit irrigation practices.