Two agronomic techniques, water deficit and severe leaf area reduction, applied with the objective of obtaining grapes with low sugar content without altering (or increasing) the polyphenol content.
For this purpose, during the years 2011, 2012, and 2013, a Merlot experimental vineyard was set up in the experimental farm of the University of Udine. In the present communication we present the results of the 2013 season. The experiment design was a full 2x2 factorial design with two levels of irrigation imposed at berry set as the first factor (I- Irrigated vines and stem water potential maintained between -0.3 and -0.6 MPa; and D-water deficit vines, with stem water potential maintained between -0.8 and -1.4 MPa). The vineyard was sheltered by a tunnel covered by EVA film and water was supplied by a sub-surface drip irrigation system. Two levels of summer trimming (applied at the end of veraison, that is when at least 80% of all berries had changed color) was the second factor. Trimmed (T) vines were manually topped above the 6th node. Non-Trimmed vines (NT) were topped at the 12th node (normal viticultural practice). Leaf area at veraison and harvest, berry composition during ripening, and non-structural carbohydrates reserves at the beginning of the trials and after were observed. Microvinification was performed for all treatments.
Results indicate that there is no interaction effect between irrigation and trimming, leading to no synergic effect on the reduction of sugars and enhancement of polyphenols. Both, water deficit and leaf area reduction heavily modified total leaf area per vine and the leaf area to fruit ratio but with different consequences in terms of grape and wine quality.
