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The objective of this research was to develop liquid calcium compound (LCa) that is useful to improve fruit quality by increasing calcium content in apple fruit. LCa was made from egg shells extracted with 5 N HCl for 12 hours at a 1:2 (w/w) in mixing ratio of egg shells to the acid. This compound contained 9.9% calcium and had 3.2 in solution pH. But the pH increased to 5.2 when diluted 60 times for tree-spray. Tree-sprays with 20-times diluted solutions (Ca 4,650 ㎍·mL^(-1)) resulted in chemical injury. Four-times tree-sprays of LCa (1,650 ㎍·mL^(-1)) resulted in higher calcium concentrations in fruit peel and outer flesh of ´Fuji´ apple fiuits than those of CaCl₂ (1,400 ㎍·mL^(-1)) or untreated one. Tree-sprays of LCa and CaCl₂ resulted in higher firmness of fruits than untreated one. But there were no differences among treatments in soluble solids content and acidity of ´Fuji´ apple fruits. No changes occurred in mixing of LCa with Mancozeb WP, a fungicide, and Methornyl LP, an insecticide, but precipitation occurred with Fenpyroximate SC, a miticide.
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