Cumulative effect (6 years) of deficit irrigation in two important cultivars of Douro region, Portugal

Abstract

Context and purpose of the study – Numerous studies have demonstrated the importance of irrigation in improving the grape yield and quality in areas with arid and semiarid climates, particularly in the context of ongoing climate changes. However, the introduction of irrigation in vineyards of the Mediterranean basin is a matter of debate, in particular in those of the Douro Demarcated Region (DDR), due to the limited number of available studies in this region. The present study aimed to evaluate how different irrigation deficits for 6 years would influence production and must quality in Touriga Francesa (TF) and Touriga Nacional (TN) varieties.

Material and methods – Field grown plants of cultivars TF and TN, were tested in a commercial vineyard, at Douro Superior sub-region, between 2015 and 2020. Vineyards are planted in a steep slope area (slope of 45%), in terraces of two rows, in a schistic and acidic soil. Three irrigation regimes were compared to a rain-fed treatment, R0, based on the estimated crop evapotranspiration (ETc): R25 (25% ETc), R50 (50% ETc), R75 (75% ETc). Irrigation was performed every 15 days, based on weather parameters recorded at the meteorological station located in the plot.

Results – Regarding the production, the number of clusters/vine in TN at different irrigation debts were as follows: R0 = R25 = R50 < R75 (11% higher). In turn, the yield was as follows: R75 > R0/R50 > R25.  In TF variety, the lowest number of clusters/vine was registered at R0 (24% lower than at R75), and the yield at all irrigation debts were higher than at R0. Considering the composition of the must of both varieties, evaluated during the six years of the trial, results showed that all irrigation debts did not change the sugar amount, pH and acidity (titratable and malic acid), nor phenolic compounds. In TN, values of pruning mass were higher at R75, while in TF the pruning mass was higher at R50. These results showed that irrigation in DDR did not significantly change berry quality traits and its effect in vine performance was inconsistent, thus suggesting that this agricultural practice should be implemented in a case-by-case scenario, depending on the cultivar, orientation, water holding capacity of the soil, microclimatic conditions, among others.