Interactions between root restriction, irrigation and rootstock treatments on the growth and cropping of ‘Queen Cox’ apple trees: Effects on orchard growth and cropping

Abstract

Summary‘Queen Cox’ apple trees on M.9 or MM.106 rootstocks were planted within root restrictive membranes buried in the soil and compared with trees planted without membranes. Half of the treated and control trees were irrigated using a trickle system and the other half did not have supplementary irrigation. Root restriction reduced greatly the extension shoot growth on the trees, by reducing the numbers and mean length of the shoots. Shoot growth on restricted trees terminated very early in the season. Irrigation, in contrast, increased the numbers of shoots and the mean individual shoot length. Root restriction reduced the mean individual size of spur and extension shoot leaves. Significant interactions between root restriction, irrigation and rootstock treatments were recorded over six seasons. Irrigation only partially alleviated the reductions in growth induced by root restriction. Root restriction increased the numbers of floral buds formed per unit trunk cross-sectional area in all years. The overall effect of root restriction was to reduce (by 50%) the annual and cumulative yields per tree, whilst supplementary irrigation had the reverse effect, increasing cumulative yields by approximately 100%. The treatments had similar effects on the yields of Class I (>65.mm diameter) fruits. Yield efficiency (yield per trunk cross-sectional area) was increased in all years by the irrigation treatment, but decreased in two of the four years by root restriction.