The Effect of Frequent Spraying with Calcium Nitrate Solutions on the Mineral Composition and the Occurrence of Bitter Pit of the Apple Cox’s Orange Pippin |
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| Authors: | BJ Van Goor |
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| Institution: | Institute for Soil Fertility, Haren-Groningen, The Netherlands |
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| Abstract: | In several commercial orchards the percentages of Ca and K in the leaves and fruit of the cultivar Cox’s Orange Pippin were determined at intervals during one or more years. The values for a series of untreated trees were continually compared with those of a comparable series of trees which were sprayed at about seven-day intervals with a Ca(NO3)2 solution. At the end of each experiment the fruit was placed in storage and later examined for the incidence of bitter pit.The Ca contents of leaves and fruit and the quotient (K+Mg)/Ca in the leaves of untreated trees showed only a moderate relationship with the percentage of bitter pit. The K content of the fruit was more closely correlated, however.The level above which much bitter pit was unlikely to occur was found to be approximately 7.5–8 mg Ca in a fruit of 140 g fresh weight.The total amount of Ca in the untreated fruit increased in a rather regular and comparable fashion in the various experiments. The rate of increase was somewhat higher during the first period of development, until the fruit reached about 20–40 g in weight, than during its subsequent growth.Spray treatments increased the Ca content of the leaves by 0.2–0.5% of the dry weight; a maximum of 4 mg Ca was added to the fruit, an increase of 47% on the basis of the amount already present. In general the Ca level increased progressively during the season with successive spray applications, and 9–15 sprays reduced bitter pit incidence to about 5%.The permeability of the fruit tissue to ions diminished as a result of the sprays, and it is suggested that an increase in cell membrane permeability may be involved in the development of the disease.For commercial orchards, more frequent sprays may need to be applied than are recommended at present to provide effective control of bitter pit. |
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