Effect of Winter Irrigation on Flowering and Fruit Set of Olea europaea L. cvs Zard and Manzanilla in Loushan Region

Flowers number and quality of olive tree is the main factor which influence on fruit and oil yield. On this case, water limitation during flowers differentiation and development in winter can reduce productivity by increasing incomplete flowers. Therefore, one of the most important times for irrigation where there is not enough rainfall in the late winter is one month before flowering, which unfortunately usually does not pay attention enough. Therefore, in this study, effect of winter irrigation with three (WI3), six (WI6) and nine days (W19) on flowering, fruit set and fruit and oil yield of two olive cultivars, Zard and Manzanilla was investigated. Rain fed irrigation (Rain fed) and common irrigation schedules in the orchard with, seven days (Control) were as a control. Irrigation of trees in treatments was performed from January to mid-April for three and a half months. The characteristics such as inflorescence number and length were measured from four main branches in each tree. Thereafter, total flowers number, complete flowers and final fruit set after natural flowers abscission was determined form six secondary shoots in each main branch. Fruit yield per tree in each treatment was calculated after fruit maturation. Furthermore, oil yield was measured after oil extraction. The Results showed there was a significant difference between different irrigation treatments for number of inflorescences, number of flowers, complete flowers, final fruit set percent, fruit yield and oil yield and fruit weight was not influence by irrigation. The best winter irrigation interval was dependent to olive cultivars so that The lowest inflorescence number, total flowers numbers, complete flowers and final fruits was found in rain fed olive tree and the highest values inflorescence number, total flowers numbers, complete flowers was found after six days interval for cv Zard and after nine days interval for cv Manzanilla. There was no significant difference between winter irrigation treatments for fruit yield, but there was a significant with rain fed tree. The highest values fruit yield was found after six days interval. Winter irrigation increased fruit yield by about 35 percent and increased oil yield by about 50 percent compared to rain fed treatment, the highest fruit yield was found after six days winter irrigation interval and highest oil yield was found nine days winter irrigation interval. Overall, winter irrigation in olive orchards could increase fruit and oil yield by increasing complete flowers number, final fruit set percentage, oil yield, and fruit weight.