Influence of the number of calcium sprays on the distribution of fruit mineral concentration in an apple orchard

Abstract

SummaryThree treatments – six, nine and twelve Ca sprays – were applied to four year old ‘Braeburn’ apple trees to establish the effect of the number of sprays on the distribution of fruit mineral concentration in the orchard. The P, K, Ca and Mg concentrations of 150 fruit and N concentration of another 150 fruit were determined two weeks before the estimated optimum harvest date and each fruit was analysed separately. At the same time a second sample of fruit was picked and stored at –0.5°C for seven weeks. After another two weeks’ storage at 17°C, fruit was examined for bitter pit development. In a second single fruit analysis the P, K, Ca and Mg concentration of 37 bitter pit and 29 bitter pit-free fruit was determined, as well as the N concentration of 27 bitter pit and 27 bitter pit-free fruit. Results of the pre-harvest analysis showed that the number of sprays affected the fruit Mg and Ca concentration, but there were no differences in N, P and K concentration between treatments. Frequency distributions of N and P were non-normal, as was the Ca distribution of the six and nine spray treatment populations. These distributions were skew with extended tails in the higher concentration class regions. This non-normality has to be taken into account when using a single mean Ca value to predict the disorder and to prevent the underestimation of the bitter pit risk. The Ca distribution of the twelve spray treatment population and the distribution of K and Mg were normal. Post-storage analysis indicated that all mineral distributions were normal, with the exception of the P distribution. Save for Ca, mineral concentrations of bitter pit and bitter pit-free fruit did not differ significantly. The bitter pit and bitter pit-free Ca distributions overlapped in the 2–3 mg 100 g–1 FW range.