NITROGEN AND CALCIUM NUTRITION AND FRUIT-QUALITY OF COMMERCIAL APPLE CULTIVARS GROWN IN FINLAND

During 1994-1995, field experiments were conducted in six apple orchar ds located in the southwest of Finland (the mainland and the Aland Isl ands). The cultivars were 'Melba', 'Raike', 'Red Atlas', 'Lobo', 'Arom a', and 'Angstrom kero'. Fruit samples were picked at about one week b efore commercial maturity and stored for three to six months at 2 to 4 degrees C and 85-95% relative humidity. During storage the percentage of physiological disorders was visually recorded. Fruit nitrogen (N) and calcium (Ca), firmness, diameter, juice titratable acidity (TA), a nd soluble solids concentrations (SSC) were determined at harvest. Nit rogen and Ca in the soil and leaves collected during fruit development were determined. The ranges in fruit N were 296-624 and Ca 27-68 mg k g(-1) fresh weight, and in the leaves N 15-23 and Ca 9-19 g kg(-1) dry matter. The N/Ca ratio was 5 and 16 and 0.9 and 2.3 in fruit and leav es, respectively. There was more variation between years in N and Ca c ontents of leaves than that of fruit. Other fruit quality characterist ics varied between seasons and cultivars. I,eaf N correlated positivel y with fruit diameter and negatively with fruit dry matter. The incide nce of physiological disorders on apples after three month storage was 2 to 13% and after six months 10 to 95%. Fruit with Ca content below 45 mg kg(-1) fresh weight were susceptible to bitter pit ('Aroma' and 'Angstrom kero') and Jonathan spot ('Red Atlas'). The cultivar 'Melba' was susceptible to bruising damages and 'Raike' and 'Red Atlas' were affected more with internal breakdown and core browning.