Calcium and Potassium Accumulation during the Growing Season in Cabernet Sauvignon and Merlot Grape Varieties

The evolution of calcium (Ca) and potassium (K) accumulation in grape berries during the growing season provided information on the productivity and quality of grape crops, considering that both elements have numerous physiological effects. The aim of the study was to determine and compare Ca and K accumulation in berries from ‘Cabernet Sauvignon’ and ‘Merlot’ grape varieties influenced by the number of days after flowering (DAF) over three consecutive growing seasons (2019–2021) in Recaş vineyards, from Banat Region in Western Romania. Results showed that Ca accumulation in the berries continued at slow rates after veraison when water was available for both varieties; accumulation was observed mainly in the skin, suggesting translocation from the flesh. Regression analysis showed a strong dependence on the interval of 65–75 DAF for Ca accumulation in the skin. K accumulation increased after the onset of veraison until 70 to 90 DAF in both varieties, with higher accumulation in the flesh than in the skin. No significant differences were found among varieties regarding the Ca and K content during the study period. In both varieties, the relationship between sugar accumulation and the Ca/K content was highly significant. Given the importance of both elements, new data may contribute to establishing the optimum grape ripeness in relation to the sugar concentration in the berries.