Effect of olive trees density on the quality and composition of olive oil from cv. Arbequina

The number of plants per hectare is a key factor for olive tree productivity. Nevertheless, information about the effect of tree density on olive oil quality and composition is scarce. Thus, the effect of planting densities of cv. Arbequina trees on olive oil quality and composition was studied along the first four years of production. Two types of planting tree arrangements were evaluated, namely olive trees planted at different distances within a row (2.0 m; 1.5 m; 1.25 m; and 1.0 m, fixing the space between rows equal to 4.0 m) or at different distances between rows (4.0 m; 3.5 m; and 3.0 m, fixing the space within the same row at 1.5 m), which led to planting densities from 1250 to 2500 trees ha−1. The results indicated that the quality parameters, composition, antioxidant activity and oxidative stability were significantly affected by the densities of plants and the crop year (P-value < 0.0001, for one-way ANOVA). An increase of plants in the row and between rows showed a tendency for a slight increase of free acidity, and a reduction of the peroxide value and of the extinction specific coefficients. Fatty acid composition was also affected, with a tendency for the decrease of C16:0, C18:0, SFA and PUFA, and an increase of C18:1, C18:2 and MUFA. The antioxidant activity and the oxidative stability also showed a reduction trend. For all parameters evaluated, the crop year had a marked influence. The year of production had significant statistical effects on the evaluated parameters, which could be related to agro-climatic factors.