TY - JOUR T1 - Defining Phosphorus Requirements for Pinot noir Grapevines JF - American Journal of Enology and Viticulture JO - Am J Enol Vitic. DO - 10.5344/ajev.2018.18016 SP - ajev.2018.18016 AU - R. Paul Schreiner AU - James Osborne Y1 - 2018/05/29 UR - http://www.ajevonline.org/content/early/2018/05/23/ajev.2018.18016.abstract N2 - A study to examine the phosphorus (P) requirements for Pinot noir was carried out using a microplot vineyard where P inputs were carefully controlled. Pinot noir grafted on 101-14 rootstock was exposed to four levels of P supply delivered via fertigation beginning in their fourth growing season. Vine nutrient status, productivity, and must chemistry were studied over four years (2012–2015), and fermentation dynamics were evaluated over three years (2012–2014). Phosphorus supply primarily influenced vine productivity by reducing leaf area at veraison and reducing yield which occurred after 3 years only in vines that received no P fertilizer. Flowering and fruit set were not altered by low P status. Phosphorus supply had the most significant impact on must P levels where the two lowest P supply treatments had lower P in musts within the first year that P was altered. However, must P concentrations as low 32 mg P/L did not influence the time for yeast to complete alcoholic fermentation. These findings suggest that P limitation reduces canopy size and yield of Pinot noir before it alters flowering parameters or reduces must P concentrations to a level low enough to alter fermentation. A P concentration of 1.0 g P/kg DW in leaf blades at veraison is proposed as the critical level where P reduces growth and yield of Pinot noir when vines are cropped at levels typical for premium wine production in the region. Growers should closely monitor vine P status when leaf blade P at veraison approaches 1.2 g P/kg DW in western Oregon Pinot noir vineyards to account for sampling and laboratory error. ER -