Response of Salustiana oranges to high frequency deficit irrigation

Summary

Mature ‘Salustiana’ orange trees under drip irrigation were subjected to deficit irrigation during three years. The water applied (including effective rainfall) in the five irrigation treatments was: (A) 60% of the evaporation of a Class A pan over irrigated grass (Control treatment); B) and C 80% and 60% of control, during the whole year, respectively; (D) 60% of control during the flowering and fruit set period; (E) 60% of control during the fruit maturation period. During the rest of the year, treatments D and E received the same amount of water as the control. There were four replicates in a completely randomized block design. Irrigation frequency was the same for all treatments. Crop evapotranspiration (ET) was estimated by the water balance method using a neutron moisture meter. ET for the control treatment was about 840 mm/year and it was reduced in the deficit treatments. Irrigation treatments affected both yield and fruit quality although the effects varied between years according to the season's rainfall. Fruit number was not affected by the irrigation treatments, therefore differences in yield were due to effect on average fruit weight. Compared to the control treatment, treatments B and C decreased yield significantly (p = 0.05) by 5% and 15%, respectively, and increased the total soluble solids and acids content of the fruit juice. Water deficit in the flowering and fruit set period (treatment D) decreased yield by 4%, acids content of the juice and peel thickness. Treatment E produced fruit of lower quality with thicker peel and more acids than the control. Treatments did not affect juice and pulp content, maturity index of fruits nor maturation time. The effects of the irrigation treatments on the water status of the trees, fruit set and abscission and their implications on irrigation scheduling are also discussed.