Juliana Pazos, Ryan Doyle, Pierre Davadant, Nataliya Shcherbatyuk, Markus Keller, and James Harbertson*
*Washington State University, 2710 Crimson Way, Richland, WA, 99354-1671 (jfharbertson@wsu.edu)

Syrah fruit and wines from a Columbia Valley vineyard trial in Washington State were evaluated. Nitrogen was applied at four different rates: to early-season soil at 0, 22.5, 45, and 90 kg N/ha and at veraison foliar at 15 kg N/ha; these treatments were denoted as control, low, medium, and high N and urea. Treatments were applied to three different vine rows in a randomized block design in 2021 to 2023. Fifteen wines were made for each vintage (five treatments, three replicates). Fruit and wine anthocyanins, grape seed, and skin tannins were analyzed for concentration (2021 to 2023) using the Adams-Harbertson assay and composition using phloroglucinolysis (2022-2023). Phenolics were measured daily during fermentation and during aging. At harvest, N-containing compounds including ammonia, yeast available nitrogen (YAN), and protein were measured. YAN and ammonia increased in the high N and urea treatments, with some exceptions. No significant differences were found in seed tannin concentrations for the three vintages, and no clear pattern was observed for skin tannins or anthocyanins. However, wine tannin concentrations were significantly greater in the control than in the high-N application treatment in the 2021 vintage, and both the control and low treatments were significantly greater than the high and urea treatments in the 2022 and 2023 vintages. Protein concentration had the opposite trend, with higher juice protein concentrations in the medium, high, and urea treatments, although the measures varied considerably. The phloroglucinolysis results show no difference in fruit tannin size or composition; however, the high N and urea treatment wines had significantly smaller average polymer size. The results show that the vineyard N applications increased ammonia, YAN, and juice protein, but the increased protein may be responsible for the reduced tannin concentration and size observed in the high N and urea treatments.

Funding Support: USDA-NIFA SCRI, Washington Wine Commission, Washington State Grape and Wine Research Program, Ste. Micelle Wine Estates (in-kind)