Nitrogen Management in the vineyard and in the winery
Nitrogen is critical to manage in wine grape production because it strongly influences vine growth and fruit quality, and because excess nitrogen can leach from the root zone. The objective of this research is to determine how nitrogen availability in the vineyard affects vine productivity and wine properties in Pinot noir and Chardonnay. It also investigates whether nitrogen additions in the winery can be used in lieu of vineyard nitrogen fertilization to boost fruit nitrogen and alter wine composition.
Importance to the Oregon wine community:
The Oregon wine industry will benefit by understanding how to manage nitrogen inputs to create desired wines, maintain productivity, and potentially reduce the environmental impact of wine production.
Progress so far:
Plots were established in a Chardonnay vineyard in 2016 and in a Pinot noir vineyard in 2017. Three nitrogen treatments were applied in the vineyard; some vines received soil nitrogen, some received foliar nitrogen, and the control vines received no nitrogen. Two additional nitrogen treatments were imposed in the winery by supplementing musts from unfertilized vines using either an organic or an inorganic nitrogen source.
Results from the Chardonnay trial showed that soil nitrogen increased vine nitrogen status (based on leaf blade and petiole nitrogen) in every year, but foliar nitrogen use did not.
Soil nitrogen also increased canopy growth and crop yield in Chardonnay in years 2 and 3, but foliar nitrogen did not alter growth or yield. The larger canopies in the soil-fertilized vines caused a slight increase in water stress in years 2 and 3, but only when all the data were pooled for each season.
Must yeast assimilable nitrogen (YAN) in Chardonnay was strongly increased by soil nitrogen application, while foliar nitrogen was less effective in boosting YAN. Fermentation rates in Chardonnay across all three years were dictated primarily by must YAN level, with the non-fertilized control treatment significantly slower than all other treatments. The foliar nitrogen musts also fermented slower than the soil nitrogen musts.
Sensory analysis of Chardonnay wines from years 1 and 2 showed that soil nitrogen use had the greatest impact on wine aroma resulting in more tropical and ripe fruit fragrances. In addition, the wines supplemented with the inorganic nitrogen source were characterized as having green or vegetal characters.
Results in Pinot noir have also shown that soil nitrogen use increased vine nitrogen status and thatfoliar nitrogen applications have not. Yield has not been altered by vineyard nitrogen applications in Pinot noir, although leaf area was greater in vines that received soil nitrogen in year 2.
Even though foliar nitrogen use did not alter leaf and petiole nitrogen status, it was just as effective in boosting must YAN levels as was soil nitrogen application. Both of the vineyard nitrogen treatments fermented slightly faster than all other musts in each year, even though the winery nitrogen additions had similar, high levels of YAN.
The sensory analysis of Pinot noir wines is not as far along as the Chardonnay study. However, early results from the 2017 vintage, and from 2016 wines produced from a different Pinot noir vineyard where this study began, indicate that soil-applied nitrogen has a greater impact on wine aroma than the winery nitrogen additions.
Further work to better characterize how vineyard and winery nitrogen use alters the sensory attributes of wines in both cultivars studied here, as well as the underlying chemistry driving these exciting differences, is ongoing.