Water relations, growth and yield of Fino lemon trees under regulated deficit irrigation

Fine lemon trees (Citrus limon L. Burm. fil.) on sour orange (Citrus aurantium L.), growing on a low water retention capacity soil, were submitted to three different irrigation treatments over four years: 100% ETc all year (T-0), 25% ETc all year except during the rapid fruit growth period when 100% ETc was applied (T-1) and 100% ETc all year, except 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 treatments, respectively. The plant responses to irrigation treatments were similar in all the years studied. Leaf water potential decreased during deficit irrigation periods in T-1 and T-2 treatments. Larger differences were found in values taken at predawn (Psi(pd)) than at midday (Psi(md)), indicating that Psi(pd) is a more useful indicator of plant water status. There was neither osmotic nor elastic adjustment in response to deficit irrigation treatment. A clear separation between the main periods of shoot and fruit growth was found, which can be considered an advantageous characteristic in applying regulated deficit irrigation strategies. Onset of the critical period of rapid fruit growth could be determined precisely by considering the decrease in relative fruit growth rate values. T-2 treatment did not induce a significant reduction in total yield, but it caused a delay in reaching marketable lemon fruit size. T-1 treatment did not affect total yield, with a reduction in yield on the first pick occurring in only one year. Chemical characteristics of lemon fruit were not significantly modified by irrigation treatment.