The Effects of Increasing the Supply of Nitrogen, Phosphorus, Calcium and Potassium to the Roots of Merton Worcester Apple Trees on Leaf and Fruit Composition and on the Incidence of Bitter Pit at Harvest

SummaryMerton Worcester apple trees in pot culture were supplied for four consecutive years with N, P, Ca and K at two rates. Apples of this cultivar differed from those of cvs Cleopatra and Jonathan both in their response to nutrient supply variations and in the interrelationships among the levels of mineral elements in the fruit and bitter pit incidence at harvest. The association between fruit levels of N, P, K and Mg previously observed in the other two cultivars was absent in Merton. In two years a positive association appeared in Merton between K level and bitter pit incidence. Doubling the K supply reduced fruit Ca level and increased protein N level and bitter pit incidence. A threefold increase in the Ca supply had the opposite effect on each of these variables. Bitter pit incidence was not affected by doubling the P supply, but was increased by supplying extra N, some of which was in the form of ammonium ion. The differences found between Merton Worcester and the two cultivars studied previously under the same cultural conditions demonstrate that any conclusions in this area concerning apples in general are valid only if they are based on findings over a number of seasons in a wide range of cultivars.