Apple orchard spraying with commercial sources of calcium to improve fruit quality

The objective this work was to evaluate the effects of different sources of pre-harvest calcium (Ca) sprays on the physico-chemical quality and bitter pit (BP) control of 'Catarina' apple fruit. The experiment was conducted in a commercial orchard in Southern Brazil in 2006/2007. The experiment used a randomized block design with four replicates. The sources of Ca sprayed on the trees were CaCl₂ (powder formulation, with two sprays at 0.4% followed by 13 sprays at 0.6%); Cal Super (15 sprays, at the doses of 2, 3 or 4 L ha^‑1), CalSOL 15 (liquid CaCl₂, with 5, 10 or 15 sprays at the dose of de 3 L ha^‑1) and Coda-Ca-L (10 sprays, at the dose of 1 L ha^‑1), in addition to CodaSal-Plus 2000 applied to the soil (two applications at the dose of 5 L ha^‑1 and 15 applications at the dose of 2 L ha^‑1) and the untreated control. The treatments started at the phenological stage J (green fruit) and finished 30 days before fruit harvest, with intervals between treatments of 10 days. Fruit were assessed at harvest for yield, weight, contents of N, P, K, Ca and Mg, starch index, flesh firmness, skin red color, soluble solids content (SSC), titratable acidity (TA) and SSC/TA ratio. The incidence of BP was assessed at harvest, and the severity of BP was assessed at harvest and after five months of cold storage (0-1°C/90-95% RH). Preharvest spraying with different sources of Ca had no significant effect on yield, fruit weight and physico-chemical quality of the fruits at harvest. The control treatment (without Ca) had incidences of BP at harvest of 46%. Preharvest sprayings with CaCl₂ (15 sprays) and CalSOL 15 (15 sprays at 3 L ha^‑1) reduced the incidence of BP at harvest (18.7 and 15.9%, respectively), without significantly changing the fruit contents of Ca, N and K in comparison to the control. The results show that the source of Ca tested did not consistently increase the Ca content in the fruit, and a great efficiency to control BP in 'Catarina' apples was achieved with CaCl₂ and CalSOL 15 (10-15 sprays, at 3 L ha^‑1).