Effect of preharvest foliar applied calcium on postharvest quality and storability of apples in Estonia

Total fruit acreage in Estonia at present stands at 12,400 hectares. However, most of apple (Malus x domestica Borkh.) orchards are quite old and therefore the crop quality is low. In 1999, a program was initiated at the Polli Horticultural Institute to investigate the possibility of raising the quality of the crop in those old orchards through foliar supply of calcium (Ca). An experiment was set up with four treatments: 1) control (untreated trees); 2) Ca(NO3)2 (one time) + CaCl2 (two times); 3) Ca(NO3)2 (two times) + CaCl2 (three times); 4) Ca(NO3)2 (two times) + CaCl2 (two times), replicated three times, using ten trees per replicate. The experimental orchard was planted in 1972-1974, at a spacing of 6 x 3 m. Six of the most important apple cultivars including ‘Antonovka’, ‘Meelis’, ‘Sidrunkollane Taliõun’, ‘Karksi’, ‘Talvenauding’ and ‘Tellissaare’ were studied. Treatments were applied starting at the last week of June and repeated until harvest. Soil and leaf samples were collected in spring and in autumn after harvest for mineral analysis. A sample of 6 kg of fruits was collected from each replicate at harvest for storage. The fruits were analyzed twice, at the beginning and at the end of storage. The results showed that the highest percentage of quality fruit (62-76%), after calcium foliar treatment, was found in the cultivar Tellissaare. Highest N and K concentration were found in leaves of ‘Antonovka’. ‘Tellissaare’ and ‘Sidrunkollane Taliõun’ had the highest concentration of microelements. The best storage results were obtained as a result of the third treatment (Ca(NO3)2(two times) +CaCl2 (three times), on ‘Sidrunkollane Taliõun’, second treatment, (Ca(NO3)2 (two times), on ‘Karksi Renett’ and fourth treatment (Ca(NO3)2 (two times) + CaCl2 (two times), on ‘Antonovka’ which had respectively, 33, 21 and 20.5% more quality apples compared to the control treatment. Our results showed that foliar treatments with calcium formulations had a positive effect on apple fruit quality and storage.