Abstract
A three-year study was conducted to investigate the accumulation of yeast assimilable nitrogen (YAN) during the final weeks of ripening in seven winegrape cultivars grown in New York State and to assess the feasibility of predicting harvest YAN using linear regression models. Berry samples of <i>Vitis vinifera</i> cvs. Cabernet franc, Chardonnay, Merlot, Pinot noir, and Riesling and interspecific hybrid cvs. Noiret and Traminette were collected weekly from 49 vineyard sites across the Finger Lakes, Hudson Valley, Lake Erie, and Long Island growing regions from August through harvest. YAN concentrations in Cabernet franc, Riesling, and Traminette were generally low, averaging <100 mg/L annually, while Chardonnay and Pinot noir had average YAN concentrations >200 mg/L. During the ripening period, linear regression models predicted harvest YAN up to five weeks before harvest (R<sup>2</sup> = 81.6%). A decrease in YAN during ripening was observed across cultivars, caused primarily by decreases in ammonia (AMM), as primary amino nitrogen levels remained stable. Population distributions were used to estimate appropriate prophylactic nitrogen additions for each cultivar, minimizing the risk of deficiency or excess; this was most difficult with Chardonnay, Noiret, and Pinot noir, which had the highest and most variable YAN concentrations and subsequently run the greatest risk of oversupplementation with prophylactic additions.
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