Productive and vegetative responses of 'Gala' and 'Fuji' apple trees under controlled irrigation strategies

We investigated the productive and vegetative responses of ‘Gala’ and 'Fuji' apple (Malus domestica Borkh.) trees to deficit irrigation and partial rootzone drying under the dry climate of central Sicily. Soil water tension (SWT), stomatal conductance, yield, fruit quality, fruit growth, and shoot extension of conventionally irrigated trees (CI), where drip emitters on both sides of each tree were left open, were compared to that of partial rootzone drying (PRD) trees, where only one side of the rootzone was irrigated for the entire season (receiving 50% of the CI irrigation water), and to that of deficit irrigated (DI) trees, where drip emitters on both sides of the rootzone were delivering 50% of the CI irrigation water for the entire season. The irrigation season started on 21 June and ended on 4 Sep, 2006. In CI trees and on the wet side of PRD trees, SWT remained generally above -50 kPa (about 80% field capacity) and followed oscillations due to irrigation cycles. In DI and the dry side of PRD trees, SWT progressively decreased to values around -200 kPa. In PRD trees, wet and dry sides were alternated at intervals of about 20 days. In both 'Gala' and 'Fuji', gs of DI trees was significantly lower than that of CI trees (52% reductions) during the entire irrigation period, while gs of PRD trees exhibited intermediate levels (24% reductions). Fruit size and fruit and shoot growth rate was similar for all treatments and in both cultivars, although 'Gala' fruits of PRD trees tended to be larger than those of CI and DI, and 'Fuji' shoots stopped growing earlier than 'Gala' shoots. In both cultivars, trees of the three treatments had similar yields, number of fruits, yield efficiency, although 'Gala' trees under PRD tended to produce less than those of the other treatments. In 'Gala', fruit quality was similar for all treatments, whereas PRD and DI fruit of 'Fuji' were firmer and better colored than CI ones. This first year of observations suggests similar potential water savings without loss of yield and fruit quality using both PRD and DI irrigation strategies in 'Gala' and 'Fuji' apple orchards, although cumulative effects of deficit irrigation could preferentially penalize yields of 'Gala' trees under the climate of central Sicily.