Evaluation of irrigation in a converted, rain fed olive orchard: The transition year

Olives for oil production are traditionally grown without irrigation. In spite of this, water application during dry growing seasons has been shown to substantially increase yields and consequently, it is becoming more and more common to find irrigation systems in established orchards in traditional regions of olive cultivation. The reported research has been initiated in order to determine the response of mature 'Souri' olive (Olea europea) trees, previously cultivated under rain fed conditions, to irrigation. Results from the initial growing season following introduction of treatments are presented. Trees in a 15 year old orchard in Bakaa el Garbiya receive one of seven irrigation treatments (0, 25, 50, 75, 100, and 125% return of reference evapotranspiration applied throughout the season or 50% annual return concentrated during predetermined growing periods). In August samplings, mid-day stem water potential, which ranged from -2.7 MPa in the rainfed to -2.1 MPa in trees receiving 125% return, was negatively correlated with water dosage. Vegetative growth rate was positively correlated to the water dosage. Fruit number was determined prior to initiation of irrigation treatments. Fruit growth rate was retarded in rain fed trees but, the increased size of irrigated fruit did not affect overall oil production per fruit as lower oil content was found in fruit from irrigated trees (22-23% compared to 27% in non-irrigated trees). Oil from irrigated trees had higher free fatty acids and lower content of polyphenol compounds. Furthermore, oil from the rain fed trees possessed higher values of positive organoleptic attributes including "fruity", "pungent" and "bitter" han oil from trees receiving maximum irrigation return. In the initial year of water application, irrigation quantity increased vegetative growth, had no quantitative effect on oil production and appeared to negatively affect oil quality. Timing of deficit irrigation was not found to have any effect on the measured parameters.