Manipulating Nitrogen and Water Resources for Improved Cool Climate Vine to Wine Quality

Low yeast assimilable nitrogen (YAN) concentrations (<140 mg/N/L) can produce wines with 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 to 2019) in Southern Tasmania, Australia, to improve YAN concentrations and observe 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. Analysis of variance was used to determine main treatment effects and treatment interactions of the measured variables for a subset of the vine population in each growing season. Increasing N rate improved YAN concentrations in both cultivars in two of three 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, inconsistent, and largely influenced by climatic conditions. Cool-climate grapegrowers would benefit from applying more N in the vineyard around veraison to improve YAN without stimulating vigor or reducing the quality of grape and wine chemical composition. Increasing irrigation rates may be advantageous in seasons with high crop load; however, current commercial irrigation rates are considered adequate.