WATER RELATIONS, GROWTH AND YIELD OF FINO LEMON TREES UNDER REGULATEDDEFICIT IRRIGATION

Fine lemon trees (Citrus limon L. Burm. fil.) on sour orange (Citrus a urantium L.), growing on a low water retention capacity soil, were sub mitted to three different irrigation treatments over four years: 100% ETc all year (T-0), 25% ETc all year except during the rapid fruit gro wth period when 100% ETc was applied (T-1) and 100% ETc all year, exce pt during the rapid fruit growth period when 70% ETc was applied (T-2) . A water saving of 30 and 20% was achieved in the T-1 and T-2 treatme nts, respectively. The plant responses to irrigation treatments were s imilar in all the years studied. Leaf water potential decreased during deficit irrigation periods in T-1 and T-2 treatments. Larger differen ces were found in values taken at predawn (Psi(pd)) than at midday (Ps i(md)), indicating that Psi(pd) is a more useful indicator of plant wa ter status. There was neither osmotic nor elastic adjustment in respon se to deficit irrigation treatment. A clear separation between the mai n periods of shoot and fruit growth was found, which can be considered an advantageous characteristic in applying regulated deficit irrigati on strategies. Onset of the critical period of rapid fruit growth coul d be determined precisely by considering the decrease in relative frui t growth rate values. T-2 treatment did not induce a significant reduc tion in total yield, but it caused a delay in reaching marketable lemo n fruit size. T-1 treatment did not affect total yield, with a reducti on in yield on the first pick occurring in only one year. Chemical cha racteristics of lemon fruit were not significantly modified by irrigat ion treatment.