Dynamics of uptake of calcium, potassium and magnesium into apple fruit in a high-density planting

Accumulation of nutrients into fruits depends on several factors, including the relative strengths of vegetative and reproductive sinks. In one experiment we assessed the accumulation of major cations in apple fruit from an irrigated, high-density orchard (7142 trees/ha), located in the Po Valley of Italy. Fruits of cvs. Braeburn, Fuji and Golden Delicious, all grafted on Pajam 1, were sampled from fruit set to harvest. The effect of frequent canopy sprays of Ca on fruit Ca content was also investigated in a second experiment. Total Ca content increased in all genotypes from fruit set to the end of August, whereas potassium (K) and magnesium (Mg) continued to accumulate throughout the growing season. Calcium and Mg concentrations were significantly higher in the peel than in the flesh at harvest, while flesh K concentration was almost twice that of peel K. Calcium sprays increased total fruit Ca content only in cv. Golden Delicious and the effect was significant only in the second half of the season. Data indicate that in the high-density apple orchards Ca enters into the fruit for a much longer period than previously suggested.