Abstract
To increase calcium content in apple fruit a trial was carried out for two years spraying commercial crystalline calcium chloride and two locally sold liquid calcium products. Furthermore two prohexadione-Ca treatments after full bloom were combined with later calcium chloride sprays. Also a new surfactant added to calcium chloride was supposed to increase the calcium uptake. All calcium chloride sprays increased the calcium content in ‘Boskoop’ and ‘Elstar’ apples compared to the unsprayed control. The best treatment in both years and both cultivars was 10 kg calcium chloride in 500 L/ha sprayed every two weeks after June drop until harvest. This treatment increased the calcium content in ‘Boskoop’ or ‘Elstar’ apples on an average by 29% or 18%, respectively. Nearly the same effect had the pre-treatment with prohexadione-Ca. The surfactant added to the calcium chloride treatment decreased the calcium content in fruits whereas the two liquid calcium formulations showed no significant effects on the calcium content compared to the untreated control. Calcium chloride sprays caused leaf injury but only single leaves were affected and no increase of fruit russetting was observed. Considering this fact and the positive effects of the calcium chloride sprays on the calcium content in apples, leaf injury should be accepted by apple growers.
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