Dr. Paul Schreiner, research plant physiologist, USDA-ARS-HCRL and OWRI, has prepared the update below. This project receives funding from the Oregon Wine Board as part of its viticulture and enology research grant program.
Paul Schreiner, USDA, and collaborators and students from Oregon State University are examining how nitrogen (N) availability in the vineyard affects vine productivity and wine properties in Pinot noir and Chardonnay, and whether N additions in the winery can be used in lieu of vineyard N fertilization to boost fruit N and favorably alter wine composition.
Replicated experiments were established in a Chardonnay vineyard in 2016 and in a new Pinot noir vineyard in 2017. The original Pinot noir vineyard where this research began in 2015 was removed from the study after showing that a shallow, alternate alleyway cultivation error boosted fruit N too much to be useful for this work. Three N treatments are being compared in the vineyard; some vines are receiving soil N, some are receiving foliar N, and the control vines are not fertilized with N. Two additional N treatments are imposed in the winery by supplementing musts from non-fertilized vines using either an organic (NutriFerm, Enartis USA) or an inorganic (di-ammonium phosphate, DAP) N source. The influence of vineyard N fertilization on vine productivity and physiology is being quantified and the impact of all N additions on wine composition is being evaluated using a sensory approach.
Findings and Next Steps
Fertilization in the vineyard boosted vine N status and fruit yeast assimilable N (YAN) levels fairly rapidly, but did not alter growth or yield until the second year, if at all. For example, soil N application increased vine N status (leaf and petiole N tests) and boosted YAN in fruit in the first year in Chardonnay and in both Pinot noir vineyards, but vine growth and yield were increased only in Chardonnay after two consecutive years of soil N use. Foliar N boosted fruit YAN as well as soil N in Pinot noir in 2017, but soil N was better than foliar N in Chardonnay.
Rates of must fermentation in Pinot noir were influenced by N treatments to a small degree each year with the soil N being consistently faster than the unfertilized control by about 1 day. For the cooler Chardonnay ferments, all N additions fermented quicker than the unfertilized control by 2 to 8 days.
The initial sensory findings indicate that the soil N treatment is producing wines that are most distinct for both varieties. The 2016 Chardonnay wines have gone through a small panel (n=9) and a large panel (n=20) for sensory analysis, while Pinot noir has been analyzed by the small panel thus far. For Chardonnay, the soil N wines are described as fruity with greater tropical notes and a round mouthfeel, while the unfertilized control wines were more floral and had a clean or fresh finish. Winery addition of DAP resulted in less ripe or green aromas in the Chardonnay wines along with a short mouthfeel, and the organic N addition in the winery produced wines with apple fruit and sulfite aromas. The small panel results from Pinot noir wines showed similar trends as found for Chardonnay.
We are continuing to monitor the impact of vineyard N use on growth and numerous physiological parameters in vines, including an analysis of roots and beneficial mycorrhizal fungi that appear to be negatively impacted by N fertilization. We will also continue evaluating the sensory properties of wines to identify how N additions in both the vineyard and winery affect wine aroma and taste.