Yield Responses of a Mature Olive Orchard to Water Deficits

Abstract

Irrigation is one of the most important means of increasing olive oil production but little information exists on the responses of olive to variable water supply. Five different irrigation strategies, full irrigation, rain fed, and three deficit irrigation treatments were compared from 1996 to 1999, in Cordoba, southern Spain, to characterize the response of a mature olive (Olea europaea L. `Picual') orchard to irrigation. Crop evapotranspiration (ETc) varied from less than 500 mm in the rain fed to ≈900 mm under full irrigation. The deficit irrigation treatments had ETc values that ranged from 60% to 80% of full ETc depending on the year and treatment. Water relations, and oil content and trunk growth measurements allowed for the interpretation of yield responses to water deficits. In a deficit irrigation treatment that concentrated all its ETc deficit in the summer, stem water potential (Ψx) decreased to -7 MPa but recovered quickly in the fall, while in the treatment that applied the same ET deficit progressively, Ψx was never below -3.8 MPa. Minimum Ψx in the rain fed treatment reached -8 MPa. Yield (Y) responses as a function of ETc were calculated for biennial yield data, given the alternate bearing habit of the olive; the equation are: Y = -16.84 + 0.063 ET -0.035 × 10-3 ET2, and Y = -2.78 + 0.011 ET - 0.006 × 10-3 ET2, for fruit and oil production respectively, with responses to ET deficits being similar for sustained and regulated deficit irrigation. The yield response to a deficit treatment that was fully irrigated during the bearing year and rain fed in the nonbearing year, was less favorable than that observed in the other two deficit treatments.