The Effects of a Sheltered Environment on the Mineral Element Composition of Merton Worcester Apple Fruits and Leaves and on the Incidence of Bitter Pit at Harvests

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Abstract
Summary The effect of shelter in reducing air movement around Merton Worcester apple trees was studied for four years. Forty-eight trees growing in pots in a glasshouse with 10% of its surface open and a further 48 trees growing outdoors were compared with respect to mineral element composition of fruit and leaves and bitter pit incidence in the fruit at harvest. The two sets of trees were subjected to the same treatments, consisting of differing combinations of N, P and Ca levels in the nutrient solution. Air movement under shelter was only one-fortieth of that outside, and maximum and minimum temperatures were slightly higher. The sheltered trees exhibited much greater terminal growth than the exposed trees and produced softer, flatter leaves. In addition, they bore fewer fruits, which were larger, softer and smoother. Both leaves and fruits from sheltered trees had higher P and K levels, and the fruits had a higher percentage of dry matter. In the first year fruit Ca was higher under shelter, and bitter pit incidence was lower in spite of the greater fruit size. However, in all subsequent years the fruit under shelter was lower in Ca and showed a higher incidence of bitter pit. The results indicate the importance of wind movement as a factor influencing vegetative growth and consequently the mineral composition of the fruit and its susceptibility to bitter pit.