Effect of the number of calcium chloride sprays on 'Jonagold' apple quality

The aim of this study was to examine effect of frequency of calcium chloride (CaCl2) sprays on 'Jonagold' apple (Malus domestica Borkh.) quality. The experiment was carried out in 1996-1998 in the Experimental Orchard of the Research Institute of Pomology and Floriculture in Skierniewice. Apple trees were grafied on M.26 rootstock and planted in 1992 at a distance of 4 x 2 m on a sandy loam soil with high available phosphorus, potassium and magnesium contents. Four experimental treatments were applied: (i) three sprays with CaCl2 solutions at 2, 10 and 18 weeks after full bloom, (ii) six sprays with CaCl2 at 2, 6, 10, 14, 16 and 18 weeks after full bloom, (iii) nine sprays with CaCl2 at 2, 4, 6, 8, 10, 12, 14, 16 and 18 weeks after full bloom and (iv) control plot - trees unsprayed with CaCl2. The results showed that fruit Ca concentration increased with the number of CaCl2 sprays during the growing season. Apples nine-times sprayed with CaCl2 solutions were smaller, less mature at harvest and after storage, had lower titratable acidity and soluble solids contents after storage and were less sensitive to bitter pit, internal breakdown and Gloeosporium-rot compared to other treatments; however these effects were influenced by the growing season. Six CaCl2 sprays only in one year of the study increased fruit firmness after storage, fruit resistance to bitter pit and internal breakdown. Three CaCl2 sprays decreased bitter pit incidence; however this effect was found only in one investigated year