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We report the results of a study carried out in a ‘Manzanilla de Sevilla’ olive orchard near Seville, Spain, where the influence of different fertigation treatments on oil chemical composition was considered. Four treatments were established: control (no fertilizer) and T200, T400, and T600 in which each tree, respectively, received 200, 400, or 600 g N per irrigation season of a 4N–1P–3K complex fertilizer applied daily from 1999 to 2003. Results shown here correspond to the last 2 years of the experiment, 2002 and 2003. Fruits were sampled at the beginning of ripeness at the “green” stage. Fruit water content increased with the amount of fertilizer, probably because of the increase of potassium in the pulp. Oil content was unaffected by the treatments, but oil yield increased with the fertilizer dose in 2003 as a result of the number of fruits per tree. Polyphenol content, which is related to antioxidant oil capacity, K225 (bitterness), and oxidative stability were lower in the oils made from trees receiving greater fertilizer doses. The monounsaturated fatty acid content, in particular oleic acid, decreased with increasing amounts of applied fertilizers, whereas polyunsaturated fatty acids, in particular linoleic acid, increased with it.
Mature `Picual' olive (Olea europaea L.) trees growing in two different localities of Córdoba and Jaén provinces, southern Spain, were subjected to annual applications of 0, 0.12, 0.25, 0.50, or 1.0 kg N/tree in the Cordoba's experiment, and to 0 or 1.5 kg N/tree in the Jaén's experiment. Nitrogen was applied 50% to the soil and 50% through foliar application in Córdoba, and 100% to the soil in Jaén. Three years after the initiation of treatments, when the trees showed differences among them in nitrogen content, fruit were sampled at maturity from each experimental tree during six consecutive seasons to determine the effect of nitrogen fertilization on olive oil quality. Tree nitrogen status was always above the threshold limit for deficiency even in control trees, indicating that most treatments caused nitrogen over fertilization. Nitrogen in excess was accumulated in fruit and, consequently, polyphenol content, the main natural antioxidants, significantly decreased in olive oil as nitrogen increased in fruit. The decrease in polyphenols induced a significant decrease in the oxidative stability of the oil and its bitterness. Tocopherol content, on the contrary, increased with nitrogen application, mainly by an increase in α-tocopherol, the main component in the olive oil. No effect was found on pigment content, particularly carotenoid and chlorophyllic pigments, neither on fatty acid composition.