The effect of irrigation and root pruning on the growth of sycamore (Acer pseudoplatanus) seedlings in nursery beds and after transplantation

Seeds of Acer pseudoplatanus were sown in November 1989 in a nursery bed and received a low or a high rate of irrigation from emergence until 30 July 1990. Shoot lengths, leaf areas and dry-matter accumulation all increased with irrigation rate. Altering the irrigation rate after this date had a negligible effect on growth. In addition, half the seedlings from each irrigation treatment were root-pruned by cutting with a wedge shaped blade pulled horizontally at 20 cm depth (wrenching) on 30 July 1990; this had a small but non-significant inhibitory effect on shoot extension. When the seedlings were lifted on 28 February 1991, the high rate of irrigation had increased the length of fine root (<2 mm diameter) by 50% but had reduced the root:shoot dry-weight ratio by 36% compared with the low rate of irrigation. The seedlings that had received the wrenching treatment had greater fine root length and root:shoot ratio than those not wrenched. After outplanting in March 1991, the shoot growth of seedlings that had previously received the high rate of irrigation was less than that of seedlings that had received the low rate. There was no significant effect of wrenching on shoot growth after outplanting, nor any interaction between the irrigation and wrenching treatments.