Foliar Calcium Application Shows Limited Impact on Fruit Calcium and Firmness in Cranberry (Vaccinium macrocarpon Ait.)

Calcium is a fundamental macronutrient for plant growth, signaling, and fruit development. High Ca concentration has been associated with improved fruit quality. The objective was to evaluate the effect of foliar calcium applications during pre-bloom and bloom on fruit calcium concentration and fruit quality. In 2022, a research site in Central Wisconsin was used to investigate the effects of calcium chloride (CaCl2) applications at concentrations of 750 mg L−¹, 1500 mg L−¹, and 3000 mg L−¹ on cranberry ‘Stevens’. Treatments were applied at four phenological stages: pre-bloom, 10% bloom, 50% bloom, and 100% bloom. Additional treatments with multiple foliar applications of 1500 mg L−¹ of CaCl2 were applied in combinations of four, three, and two of the phenological stages described above, and fruit firmness and Ca content were evaluated at harvest. In 2023, the study was expanded to include two additional experimental sites, another cultivar, and a different Ca fertilizer. In 2022, single foliar Ca applications were ineffective in increasing fruit Ca content. However, multiple applications of 1500 mg L−¹ CaCl2 during bloom increased fruit Ca content but without improving firmness. In 2023, multiple applications during bloom had no significant effect on fruit Ca content or firmness across all treatments, cultivars, and sites. These contrasting results suggest that seasonal variation may influence the efficacy of foliar calcium applications in cranberry. Overall, fruit with higher Ca content were firmer during storage. These findings underscore the role of fruit Ca in cranberry quality, providing insights for future studies aimed to enhance cranberry fruit quality.