Impact of irrigation in production and oil properties in intensive and hedgerow olive groves

The Alentejo region in southern Portugal is characterized by a Mediterranean climate of mild temperature associated with annual rainfall in winter and hot and dry season in the summer, demanding a frequent irrigation in this season. This work evaluates the effects of irrigation management on the quantity and quality of olive oil produced in an intensive grove of the cultivar 'Cobrançosa' (grove FEA) and in a hedgerow olive orchard of the cultivar 'Arbequina' (grove OS), both located in Alentejo near Évora. In both orchards, the usual farmer daily drip irrigation (emitters with flow of 1.6 l/h, spaced 1 m apart and emitters with flow of 2.3 l/h, spaced 0.75 m apart, respectively in FEA and OS) was compared with an excessive water supply (emitters with flow of 2.3 l/h, spaced 1 m apart, in 'Cobrançosa' orchard) or a deficit irrigation strategy after middle of July (new emitters with flow of 1.6 l/h, spaced 0.75 m apart, in 'Arbequina' grove). Measured variables were average fruit weight, maturity index, oil content on a dry matter basis and total production/tree. First results show that in the intensive grove there are no significant differences in total production and in the maturity index between the two treatments, whereas the average fruit weight was slightly lower and the oil content in dry matter basis was slightly higher in the standard irrigation strategy. In the hedgerow orchard, average fruit weight and oil content in the dry matter were slightly higher in plants with usual water supply and the total production was significantly higher in this case, whereas maturity index increased slightly in the deficit irrigation treatment. In both groves, olive oil quality did not show significant differences between the two irrigation treatments and fulfilled the characteristics for an extra virgin olive oil, the one with the highest economic return. These results suggest that there is no advantage in the excessive irrigation in 'Cobrançosa' orchard whereas the deficit irrigation appears as too stringent in the 'Arbequina' orchard.