Nataliya Shcherbatyuk, Markus Keller,* and Pierre Davadant
*WSU, Prosser IAREC, 24106 N. Bunn Rd., Prosser, WA, 99350 (mkeller@wsu.edu)

Vineyard nutrient management is critical to reach quality standards, yet timely evaluation of nutrient status remains challenging. The existing sampling protocol of collecting leaf blades and/or petioles at bloom or veraison is late for in-season fertilizer applications. Early-season protocols are necessary to predict seasonal vine nutrient demand. This project aims to 1) optimize tissue sampling protocols; and 2) determine the amount of nutrients removed at the end of the growing season. Field trials were initiated in 2020 and conducted in 2021 and 2022 in commercial vineyards in arid eastern Washington. Three rates of K were applied in Chardonnay, and three and two rates of N were applied in Syrah and Concord, respectively. Dormant canes, shoots (five to six-leaf stage), leaves (blades and petioles) at bloom and veraison, fruit at lag phase and harvest, and all leaves at leaf fall were collected for nutrient analysis. Yield components and fruit composition were determined at harvest. Fertilizer treatments did not affect tissue nutrient status, except that Chardonnay blades at veraison had lower K where no K was applied. In Chardonnay, Syrah, and Concord, P and K concentrations in shoots correlated with those in blades and petioles at bloom in 2021, but not in 2022. More work is required to draw firm conclusions regarding early-season sampling. Fruit harvest and leaf fall removed significant amounts of nutrients. The harvested fruit contained more N in 2021 than in 2020 and 2022, and N and K in Concord was much higher than in winegrapes in 2021 and 2022, but not in 2020. Leaf fall removed lower amounts of nutrients after a long, frost-free postharvest period (2021) than when leaves were killed by frost (2022). Seasonal differences should be considered when developing vineyard nutrient budgets for fertilizer recommendations based on harvested fruit and potential nutrient removal from vineyards by wind.

Funding Support: USDA-NIFA-SCRI, Washington State Grape and Wine Research Program, Washington State Concord Grape Research Council