Timing of Foliar Calcium Sprays Improves Fruit Firmness and Antioxidants in “Liberty” Blueberries

Highbush blueberries require proper agronomic management in order to produce high quality fruits. Calcium (Ca) has been applied in many fruit crops due to its well-established role in improving fruit quality. Our aim was to study the effect of foliar Ca sprays at different timings (early: fruit set, 8 and 16 days after fruit set-dafs; or late: 16, 24 and 32 dafs) and rates (400 or 800 g Ca ha−1) on fruit quality and antioxidant features. Five Ca treatments were applied: control, early low Ca, early high Ca, late low Ca, and late high Ca to 9-year-old “Liberty” highbush blueberries in Perquenco, Araucania Region, Chile (38° 43′ 88 ″ LS), for two seasons: 2014/15 and 2015/16. Berry quality variables were analyzed at each harvest. Fruit antioxidants properties and Ca concentration in fruits and leaves were measured at 30 and 1 day before harvest (dbh), as well as the initial, middle, and final harvests. There were no significant interactions and treatments effects on berry weight, yield, fruit size, titratable acidity (TA), and total soluble solids (TSS). Significant interactions (Ca rate x spray timing) were registered for fruit firmness throughout the study and consistent effects were detected for Ca contents in fruits and leaves at harvest but not 30 and 1 dbh. High positive correlations between fruit firmness and fruit Ca concentrations were found. Early spray treatments consistently resulted in increased fruit firmness and had better antioxidant response compared to control and late Ca application treatments.