Effect of reduced irrigation on grapevine physiology, grape characteristics and wine composition in three Pinot noir vineyards with contrasting soils

The effect of water stress on grapevine performance has been extensively studied in different wine producing regions around the world, but little has ocurred in New Zealand. Pinot noir is the second most planted variety in the country and the most planted in Waipara. An improved understanding of the physiological responses of Pinot noir vines growing in different soils under a water restricted scenario is crucial for winegrowers, because vineyard irrigation is commonly practiced in Waipara and water is expected to become scarcer in future seasons. Three Pinot noir vineyards having similar characteristics, but planted in three of the most representative types of soil of the Waipara region were selected to investigate the effect of reducing irrigation by about 50% under commercial conditions. Control (CON) vines corresponded to those receiving the irrigation applied according to the viticulture manager’s criteria, and a reduced irrigation (RI) treatment was implemented by modifying the drippers spacing and flow rate. The experiment was carried out during the 2013-2014 and 2014-2015 seasons. Edapho-climatic characteristics were compared within the region and among the three sites. “Terroir” provides the link between wine composition and place of origin. Thus, soil and climatic conditions, were characterised to understand the uniqueness of Pinot noir wines produced in Waipara. Differences in soil profile available water were found between the three types of soil. Also, variations in temperatures, wind speed and evapotranspiration, among other parameters were found within the region as well as between sites. A range of analyses was used to identify differences in grapevine physiology between vines under RI and those normally irrigated. Primary leaf area abscission and stomatal closure were short-term responses to water stress, which together with the lack of differences in stem water potential suggested the isohydric behaviour of Pinot noir under the conditions of this study. Other parameters like carbon isotope ratio, leaf proline content and root carbohydrates were little affected by RI. Berry weight was reduced by the treatment, but this varied depending on the site and season. Seed water content, seed fresh and dry weight were unaffected by RI which may suggest that seeds remain “isolated” from the rest of the berry from veraison onwards, even under moderate water stress. Taurine was found in berry juice, the first time that this nitrogen compound is described in Vitis vinifera L. Wines produced during the first season showed differences in wine titratable acidity (TA), colour and aroma profile by GCMS only at the site having the lowest profile available water, while wines from those sites with high and very high profile available water did not report differences between CON and RI for most of the parameters evaluated. This study demonstrated the edapho-climatic variability within the Waipara region, as well as the adaptive responses to water stress site by site, confirming irrigation as one of the main factors modifying “terroir” expression. From a practical perspective, the findings suggest merit for the use of reduced irrigation in vineyard management, as a means to save cost whilst maintaining grape quality.