Effect of row spacing on olive 'Arbequina' oil quality within north-south-oriented hedgerows

Row spacing is a fundamental aspect of olive hedgerow design that modifies row length per area, tree density, amount and distribution of irradiance intercepted by the canopy, and consequently the production and quality of oil. An experiment was established in 2008 in Toledo, Spain, with north-south rows at three row spacings, 5.0, 4.0 and 2.5 m, to evaluate the impact of spacing on oil quality. The hedgerows were maintained by lateral pruning and topping to the same width (1 m) and height (2.5 m). In 2012 and 2013, fatty acid contents were measured in oil obtained from fruits harvested from each face (east and west) of the hedgerows in six height layers, 0-0.4, 0.4-0.8, 0.8-1.2, 1.2-1.6 and 1.6-2.0 m above ground and also from the top (>2 m). Overall hedgerow oil quality parameters were calculated as mean weighted concentration of oil yield across faces and layers. Reduction of row spacing from 5.0 to 2.5 m reduced the concentration of linoleic acid from 8.6 to 7.8%, while the concentrations of the remaining fatty acids were similar between row spacings. Regardless of spacing, oil quality was similar on east and west faces. Concentrations of palmitoleic, palmitic, stearic and linoleic acids were higher at the top than the base of the canopies while oleic acid showed the reverse trend. Differences between the top and the lower layers increased as row spacing was reduced. Fatty acid contents were significantly related to the irradiance received by the fruits during the oil synthesis period. The concentrations of palmitic (R-2=0.76), palmitoleic (R-2=0.46) and linoleic (R-2=0.76) acids increased, while that of oleic acid decreased (R-2=0.75), linearly with daily irradiance from 6.0 to 15.5 mol photosynthetically active radiation m(-2). Analysis of the relationships between irradiance and oil quality can help to improve the design and management of olive hedgerows destined for oil production.