Estudio del efecto de la aplicación de diferentes estrategias de riego al olivo (olea europaea L.) de la variedad arbequina sobre al composoción del aceite

Abstract

Olive tree has been regarded as a dry farmed crop since it has enough resources to adapt to the arid zones of the Mediterranean basin. From a productive point of view, it responds favourably to small additional amounts of water besides the rain, despite being its water requirements high. Taking into account that water availability is a considerable constraint in agriculture, it is important on the one hand to determine the olive tree water requirements for a correct use of this resource and on the other hand, to evaluate irrigation strategies tending to reduce water supplies without affecting production and quality. The main objective of the present work is based on the assessment of olive oil quality. The effect of two irrigation strategies has been studied: a regulated deficit irrigation strategy (RDC)and a linear irrigation strategy, in olive trees cv. Arbequina grown under the area of the Protected Denomination of Origin Les Garrigues (Lleida), on the quality, chemical composition and organoleptic characteristics of the oils obtained. Regulated deficit irrigation strategy experiment was located in a commercial orchard of mature olive trees during three years (1996-1998), applying 4 irrigation treatments corresponding to a control treatment (100% ETc) and three RDC treatments, irrigated like the control but applying only the 75%, 50% and 25% of the control dose during the period ranging from the massive pit hardening (mid July) to the end of September (treatments RDC-75, RDC-50 and RDC-25 respectively). From the olive oil quality point of view, it can be said that oils from the most deficitary irrigation treatment (RDC-25) are the ones which significantly differ from those of the control treatment. Oils from RDC-25 treatment are characterised by a higher level of polyphenols and consequently, by a higher oxidative stability. The bitter index of these oils is slightly higher than for the control treatment, a fact confirmed by the results of the sensorial analysis. These oils are also characterised by a higher intensity of the fruity attribute and a slightly higher overall grading. As a conclusion of this part, it can be affirmed that RDC-50 and RDC-75 strategies lead to important savings of irrigation water without affecting oil quality and oils slightly more stables and fruity are obtained. The linear irrigation experiment was located in a commercial orchard of young olive trees for two years (1998-1999), applying 7 irrigation treatments defined according to the crop coefficient (Kc) (Kc= 0.25, 0.38, 0.50, 0.57, 0.64, 0.71 and 0.85, corresponding to T1 to T7 treatments respectively). From the quality point of view it can be said that the supply of increasing amounts of irrigation water to young olive trees cv. Arbequina under these trial conditions, although has no effect on the classical quality parameters of olive oil, it does have a clear effect on the photosynthetic pigments and phenolic content of the oil. In the oils from the most irrigated treatments, T6 (Kc=0.71) and T7 (Kc=0.85), there is a marked decrease of chlorophyll and carotenoid pigments content as well as phenolic content, which implies a decrease on oxidative stability and a lower bitter index. On the other hand, oils from the less irrigated treatments, T1 (Kc=0.25), T2 (Kc=0.38) y T3 (Kc=0.50), show a high level of phenols and consequently a higher resistance against oxidation, but with the disadvantage of being excessively bitter oils. From the quality point of view, the most suitable treatments are located in the intermediate conditions, which would correspond to T4 (Kc=0.57) and T5 (Kc=0.64) treatments.