Potassium Requirements for Pinot noir Grapevines

Abstract

The potassium (K) requirements of Pinot noir grapevines were studied in a microplot vineyard, where four levels of fertilizer K supply were carefully controlled. Vine nutrient status, productivity, and must chemistry were studied over four years, and fermentation dynamics were evaluated over three years. Vine productivity, based on leaf area, pruning weights, and yield, was reduced by K supply only after four years in vines receiving no K fertilizer. K deficiency symptoms were apparent on leaves and fruit in vines receiving no K the year before productivity was altered, and after must pH was already reduced. 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 years 3 and 4 in vines receiving 20% K. Late bunch stem necrosis occurred on some fruit clusters in year 3 in vines receiving no K and 20% K; this increased dramatically in year 4 in the no-K vines. Low must pH values of ~3.0 and must K concentrations as low as 600 mg K/L did not influence the rate of 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 dry weight (DW) at veraison is proposed as the critical concentration for Pinot noir vines cropped at levels typical for the region. Growers should monitor vine K status closely 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.