Manipulating nitrogen and water resources for improved cool climate vine to wine quality

Low yeast assimilable nitrogen (YAN) concentrations (<140 mg/N/L) can result in wines of inferior aroma and flavor, regardless of supplemental nitrogen (N) additions in the winery. The impact of doubling commercial field N and irrigation rates was explored in Vitis vinifera L. cv. Chardonnay and Pinot noir over three growing seasons (2016 -2019) in Southern Tasmania, Australia, with the aim of improving YAN concentrations and observing the concurrent influence on vine canopy, yield, and grape and wine composition. Six combinations of irrigation and N rates were applied to 20 vines for each treatment combination and replicated across both cultivars. The treatments included, the standard irrigation rate (~530 L/vine/year) / control N (0 kg/N/ha/year) rate, standard irrigation / standard commercial N rate (~18 kg/N/ha/year), standard irrigation / double commercial N rate (~36 kg/N/ha/year), double irrigation rate (~1060 L/vine/year) / control N, double irrigation / standard N and double irrigation / double N. ANOVA was used to analyze main treatment effects and treatment interactions on the measured variables for a sub-set of the vine population in each growing season. Increasing N rate improved YAN concentrations across both cultivars in 2 out of 3 growing seasons, with the double N rate associated with increasing YAN to acceptable (>140 mg/N/L) levels. Irrigation had no impact on YAN concentrations. Treatment influences on vine vegetative growth, yield, and grape and wine composition were marginal and inconsistent, and were largely influenced by climatic conditions. Cool-climate grape growers would benefit from applying more N in the vineyard around veraison to improve YAN, without stimulating vigor and negatively impacting chemical grape and wine composition. Increasing irrigation rates may be advantageous in seasons of high crop load, however current commercial irrigation rates are considered adequate.