Effects of High Rates of Potassium Fertilization on Raw Product Quality and Changes in pH and Acidity during Storage of Concord Grape Juice

Excessive levels of potassium (K) fertilizer (225 to 900 kg/ha) were applied to Concord grapevines for five years in a vineyard with adequate initial levels of petiole K. Petiole K increased from 1.24% (dry weight basis) in control plots to 6.07% in high K plots. Petiole Ca and Mg showed highly significant negative correlations with petiole K, while Mn decreased only slightly with K fertilization. Juice K increased with high levels of K fertilization, resulting in pH increases and titratable acidity reductions in the juice. As fresh juice K content increased, significant increases in pH and acidity loss occurred during juice storage. K levels in the fresh juice and acidity and K loss during storage were highly correlated. K fertilization did not affect total pigment content of the juice, but tristimulus color values were reduced, probably through K-induced pH effects on the anthocyanin molecule. K fertilization reduced the amount of green fruit present at harvest, but had little effect on % soluble solids.