Responses of young clementine citrus trees to water stress during different phenological periods

Citrus (Citrus clementina Hort. ex Tan., cv. Clementina de Nules) were subjected to water stress by withholding irrigation in three periods of the year corresponding to three phenological stages of tree development during 1993 and 1994. Predawn leaf water potential (Psi(a)) was measured in representative treatments during each period and the water stress integral (S-Psi) calculated for all treatments. Actual tree evapotranspiration (ET) was calculated by soil water balance during the intervals of no irrigation and extrapolated from a weighing lysimeter during the irrigation intervals. Both S-Psi and ET were found to be good stress indexes with respect to yield and growth parameters, but ET was a better yield predictor. Yield was reduced by severe water stress during each period of the year, but the most sensitive phenological stages were the flowering and fruit set periods. Fruit quality and vegetative growth were affected mainly during the ripening period. A linear correlation was found between relative yield reduction and relative ET deficit with a slope of about 2.0, indicating a higher sensitivity of 'Clementina de Nules' citrus trees to water stress than earlier results on other citrus cultivars.