Irrigation Effects with Different Mixtures of Olive MillWastewater (OMW) and Clean Water on the Growth and Quality of Young Olive Plants cv. ‘Ottobratica’, in a Nursery

This study examines the effects of olive mill wastewater (OMW) combined with clean water (CW) in a nursery of olive plants (Olea europaea L.). Four treatments (Control = 0%, T1 = 5%, T2 = 18%, T3 = 46% OMW) were compared. From July to November, the amount of OMW given to cv. ‘Ottobratica’ olive plants ranged from 0 ml in control plants to 1540 ml per plant in T3. The increase in shoot development was higher in T1 (6.25 cm) and in T2 (4.51 cm) compared to the control plants (1.96 cm). In T3 a decrease in shoot development (0.88 cm) was evident. Absorbent root length was statistically higher in T1 (157 m) than in T2 (85 m) and T3 (74 m), decreasing as the OMW% in the mixture increased. Stomatal conductance increased by 144% in T1, 35% in T2 and 42% in T3 compared to control plants. In T1, T2 and T3 the leaf area and stomatal conductance decreased with a reduction in length of the absorbent roots due to the higher OMW% in the mixture. The potassium level was highest in T1 but no significant differences were observed in the other treatments compared to the control. The total dry weight per plant increased by 28% in T1 and decreased ~12% in T2 and T3, compared to the control plants. OMW, if diluted, can be considered a valid fertilizer and interesting ecological and economic solution in olive nurseries.