Effects of tree age at planting, root manipulation and trickle irrigation on growth and cropping of apple (Malus pumila) cultivar Queen Cox on M.9 rootstock

The apple cultivar Queen Cox on M.9 rootstock cropped more precociously when planted as two year old trees than when planted as one year old trees, even though there were no significant differences in the sizes (leader height and branch length) of the trees at the time of planting. However, the two year old trees had larger root systems at planting. As the trees aged, those planted as one year olds grew more vigorously and bore higher cumulative yields than those planted as two year olds. Annual root pruning of the trees, commencing 15 months after planting, reduced extension shoot growth, crown volume, and grubbing weights (final fresh weights of scions) severely. In some seasons root pruning increased the number of spur and terminal floral buds produced and also the final sets and yield efficiencies on the treated trees. Planting trees within semi-permeable fabric membranes also reduced extension shoot growth and tree size, but less severely than the root-pruning treatment. Root restriction increased the efficiency of fruit set and yields and also improved the grades of fruits produced. Trickle irrigation treatments increased shoot growth and tree, fresh weight. at the time of grubbing, but had inconsistent and small effects on fruit set and yields. Interactions between tree age at the time of planting and the root manipulative treatments were significant.