The effects of environment and cultural practices on calcium concentration in the apple fruit

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Abstract
Calcium concentrations in bulked samples of randomly selected apples from field trials are dependent on orchard environment and management in addition to nutrition. Concentrations in individuals within each sample vary widely and adequate numbers of fruit must be analysed to detect the relatively small changes in mean concentrations induced by orchard treatments. Since there is an inverse curvilinear relationship between calcium concentrations and mean mass per apple (average curves may differ according to scion cultivar), concentrations can be altered by factors affecting fruit size. Hence, excessive thinning or irrigation can lower calcium concentration and, at East Mailing, manurial (N, P, K) and soil management treatments have had little effect other than via fruit size. Significant deviations from the average curve can occur as a consequence of weather conditions during the growing period and sometimes because of biennial tendencies. Soil applications of calcium sulphate, of sodium nitrate late (rather than ammonium sulphate early), late summer pruning, and judicious irrigation can all increase calcium concentrations slightly without altering fruit size. It is suggested that the combination of all these treatments, and an effective calcium spray programme could result in large increases (eg from 35 up to 60 ppm fresh weight) in calcium concentrations.