Abstract

Many irrigation strategies have been proposed in olive orchards to overcome both increasing water scarcity and competition for water with other sectors of society. However, threshold values of stomatal conductance (g(s)) and stem water potential ((stem)) for use in designing deficit irrigation strategies have not yet been adequately defined. Thus, an experiment was conducted to determine g(s) and (stem) thresholds for water stress in a super-intensive olive orchard (cv. Arbequina) located in Pencahue Valley (Maule Region, Chile) over three consecutive growing seasons. The experimental design was completely randomized with four irrigation treatments. The stem water potential ((stem)) of the T-1 treatment was maintained between -1.4 and -2.2MPa, while the T-2, T-3,T- and T-4 treatments did not receive irrigation from fruit set until they reached a (stem) threshold of approximately -3.5, -5.0, and -6.0MPa, respectively. Stomatal conductance (g(s)), transpiration (T-l), net CO2 assimilation (A(n)), and stem water potential ((stem)) were measured fortnightly at midday. A significant nonlinear correlation between A(n) and g(s) was used to establish different levels of water stress. Water stress was considered to be mild or absent when the g(s) values were greater than 0.18molm(-2)s(-1), whereas water stress was estimated to increase from moderate to severe as g(s) decreased significantly below 0.18molm(-2)s(-1). Similarly, water stress using (stem) was determined to be mild or absent above -2.0MPa. Such categorizations should provide valuable information for maintaining trees well-watered in critical phenological phases.