Effect of Regulated Deficit Irrigation on Vegetative Growth, Fruiting, Stomatal Conductance and Water Use Efficiency in 'Nules' Clementine under Arid Conditions of the Souss Valley of Morocco

The Souss valley of Morocco is its major citrus producing area but is subjected to water scarcity, resulting in negative effects on citrus yield and quality. This research aims at contributing to the development of irrigation strategies for citrus which resulted in water economy and that they do not affect negatively fruit yield or quality. Threeregulated deficit irrigation (RDI) treatments were tested on 5-year old 'Nules' clementine trees (Citrus reticulata) grafted on Citrus macrophylla. Water supply was done daily according to tree phenological stage and local experience which was then compared to crop water needs calculated based on base evapotranspiration (ETo). From 1 Oct. 2011 to 30 Jan. 2012, all trees received the same amount of water (129 mm). The trial started on 1 Feb. 2012 just prior to bud break with a supply of 0.9 to 1.8 mm/day, depending on treatment. The dosage increased with increasing ambiance temperature to reach supply duration of 2h 40 min during hot summer days (supplying 2.7, 3.5 and 2.1 mm/day respectively for T0, T1 and T2). Total water supply was 627 mm for T0 (= 84% ETc), 752 mm for T1 (= 106% ETc), 512 mm for treatment T2 (= 68% ETc), applied during the trial period corresponding to 2011-12 cropping season. Results indicated that the local irrigation strategy did not match up with crop water needs. During the crop cycle studied here temperatures were very high reaching 48 degrees C and relative humidity as low as 10%, particularly during fruit set and fruit growth. Stressed trees had more flowers, reduced vegetative growth, lower fruit set, lower final fruit size and yield. Stomata conductance decreased with water deficit while tree water use efficiency increased.