Root pruning reduces the vegetative and reproductive growth of apple trees growing under an ultra high density planting system

Braeburn, Royal Gala, Oregon Red Delicious, Splendour, Granny Smith and Fuji/MM.106 apple (Malus domestica Borkh.) growing under an ultra high density planting system were manually root pruned, with a sharp spade, prior to 4th leaf in early Spring (September) 1994, along both sides of the row and between trees, 20 and 30 cm from the trunk, to the depth of 30 cm. The soil was duplex soil with all lateral roots lying in the top 30 cm. Root pruning effects were evident in both the 1st and 2nd years after treatment with the more severe effect being for the more severe pruning. Severe (20 cm from trunk) root pruning decreased tree height by 12%, shoot length by 12%, tree and shoot diameter, and number of branches per tree compared to the control. Severe root pruning increased the number of flowering spurs per selected shoot (from 2.4 to 4.2) and on the main stem (from 9.4 to 20) in the 1995/1996 season. Total yield (3.3 to 1.2 kg tree(-1) in 1994/1995, 4.1 to 2.6 in the 1995/1996 season) and average fruit size (146 to 128 g in 1994/1995, 129 to 107 g in 1995/1996 season) decreased in both seasons. This suggested a lack of balance between the reproductive components and potential yield. Part of this can be explained by reduced bourse and shoot (6.2 to 4.5 leaves per shoot in 1994/1995) leaves for carbohydrate supply to the developing fruits. (C) 1998 Published by Elsevier Science B.V. All rights reserved.