Matthew Fidelibus

Calcium (Ca) is a critical macronutrient for all plants, including grapevines. The divalent cation (Ca2+) serves structural roles in cell walls and membranes, is an important counter‐cation for inorganic and organic anions in the vacuole, and is an intracellular messenger in the cytosol. Calcium is among the most abundant elements within Earth’s crust and is present in various soil minerals, including phosphates, silicates, sulfates, and carbonates.

Potassium (K) is an essential nutrient that fulfills critical functions including enzyme activation, osmotic adjustment, turgor generation, cell expansion, regulation of membrane electric potential, and pH homeostasis.

Berry sugar and anthocyanin accumulation are key factors in determining the fruit quality of red wine grapes in the San Joaquin Valley (SJV), where >70% of California wine grapes are grown (California Grape Crush Report 2022). Hot climates are not ideal for red Bordeaux cultivars such as Cabernet Sauvignon and Merlot as anthocyanin accumulation is inhibited (Figure 1). However, fruit quality might be improved with certain management practices, including deficit irrigation and leafing.