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Wine Grape Tissue Nutrient Concentrations in the Inland Pacific Northwest

Soil and plant tissue testing is routinely used by growers to assess the status of their crops to determine what, if any, supplemental fertilizers are needed to reach both quality and quantity production goals. In wine grape (Vitis vinifera L.) production, leaf tissue testing is often used as the primary assessment tool for in-season fertilizer adjustment. In this project, we conducted a 3-year survey to evaluate actual leaf nutrient concentrations for comparison with published tissue nutrient guidelines. Leaf petiole and blade samples were collected from six different wine grape cultivars (two white, four red) from eight different sites that geographically encompass Washington's Columbia Valley American Viticultural Area (AVA) (inclusively), the Milton–Freewater area in Oregon, and the Parma area in Idaho. These are all low-rainfall areas (<450 mm/year) in the Pacific Northwest (PNW). Leaf samples (petioles and blades) were collected at bloom and veraison and analyzed for nutrients by a commercial laboratory. Concurrently, replicated nitrogen (N) rate trials were conducted on two Riesling and two Merlot vineyards in the Columbia Valley AVA. The same tissue-sampling technique was employed on grapevines receiving from 0 to 67 kg ha–1 N for up to 4 consecutive years. Results from the vineyard survey and from the N-rate trials show that many of the nutrient concentrations in the sampled tissues fall outside of the ranges currently considered normal or adequate in published standards. However, grapes from the survey and trial sites were all of sufficiently high quality for production of premium wines. This suggests that currently published standards are not appropriate for use in regulated deficit-irrigated wine grapes in the low rainfall areas of the inland PNW.