Potassium requirements for Pinot noir grapevines

Authors: Schreiner, Roger; OSBORNE, JAMES - Oregon State University

Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2019
Publication Date: 10/11/2019
Citation: Schreiner, R.P., Osborne, J. 2019. Potassium requirements for Pinot noir grapevines. American Journal of Enology and Viticulture. 71(1):33-43. https://doi.org/10.5344/ajev.2019.19043.
DOI: https://doi.org/10.5344/ajev.2019.19043

Interpretive Summary: Grape growers rely on tissue nutrient tests to diagnose mineral nutrient health of vineyards and guide management practices such as fertilizer and irrigation applications. However, the standards used to assess grapevine nutrient status from tissue tests have been based on obtaining high yields in warmer regions. These standards may be too high for wine grapes grown in cool regions leading to excessive nutrient applications and potential losses to the environment. In addition, the manner that potassium alters vine productivity and fruit quality for wine grapes produced at typical crop levels for the region was not known. The potassium requirements for grafted Pinot noir grapevines were thus evaluated over four years using a pot-in-pot vineyard that allowed for precise control of this nutrient. The impact of potassium on vine vegetative and reproductive growth parameters, and on fruit composition and fermentation behavior of musts was used to define potassium needs and these were equated to leaf and petiole tissue tests. Reducing potassium supply had the greatest impact on must potassium levels and pH, well before vine productivity was reduced or potassium deficiency symptoms had developed. Guidelines to better manage potassium in Pinot noir vineyards were defined and this information will allow producers to maintain or improve quality, increase profits, and protect the environment.

Technical Abstract: The potassium (K) requirements of Pinot noir were studied in a microplot vineyard where K inputs were carefully controlled. Pinot noir grafted on 101-14 rootstock was exposed to four levels of K 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). Vine productivity based on leaf area, pruning weights, and yield was reduced by K supply only after 4 years in vines receiving no K fertilizer (no K) and when leaf blade K at veraison was about 4 g K/kg DW for two consecutive years. Potassium deficiency symptoms on leaves and fruit occurred in the no K vines a year before yield was altered while must pH was altered prior to that. Must pH was reduced below the level of control (100% K) vines in year 2 and thereafter in vines receiving no K and also in year 3 and 4 in vines receiving 20% K. Those treatments where must pH was reduced had veraison leaf blade K values below 5.5 g K/kg DW. Late bunch stem necrosis (LBSN) occurred on some fruit clusters in year 3 in vines receiving no K and 20% K and this increased dramatically in year 4 in the no K vines. Low must pH values of about 3.0 and must K concentrations as low as 600 mg K/L did not influence the time for yeast to complete alcoholic fermentation. These findings indicate that monitoring must pH in addition to leaf blade or petiole K concentrations would be helpful in managing vine K status. A leaf blade K level of 6.0 g K/kg DW at veraison is proposed as the critical concentration for Pinot noir vines cropped at levels typical for the region. Growers should closely monitor vine K status and must pH when leaf blade K at veraison approaches 7.0 g K/kg DW in western Oregon Pinot noir vineyards to account for sampling and laboratory error.