Potassium availability in soil, potassium uptake and effects on the pH of musts and wines

Abstract

The pH values of South Tyrolean musts and wines are high in most years. The high pH values are not only related to the low content of organic acids of the grapes at maturity, they are also the result of high potassium levels in the must. It should therefore be examined whether vineyards with low potassium uptake would produce musts with lower pH-values and if it would be appropriate to focus even more on a targeted and possibly even lower potassium availability for the vines. For this purpose, three sites, which repeatedly showed low levels of potassium in the leaves in recent years, and three better supplied sites have been studied for potassium levels in the soil, in the leaf and from the musts to the finished wine. It turned out that all sites, even the moderately supplied ones, still had too high potassium contents in the soils to cause significantly lower potassium contents in the musts. Even in years with very low potassium levels in the leaf during flowering and early ripening, more than 1.5 g/l of potassium were still found in the musts. In pronounced periods of drought, which have been more frequent in recent years as a result of climate change, the potassium uptake by the vine is severely limited as long as the drought persists, but the deficiencies can be quickly compensated for as soon as higher soil moisture is present.