Effect of root wrenching in the nursery on the quality of Japanese larch transplants.

Abstract

The influence of root undercutting and wrenching in the nursery on the quality of two-year-old Japanese larch (Larix kaempferi) seedlings was investigated. Seedlings were undercut in June and then subjected to a factorial combination of wrenching in July, August and October. All treated stock plus one set of controls (not undercut or wrenched) received additional fertiliser. The effect of these treatments on the phenology of height growth and bud flushing the following spring, end-of-season morphology and root growth potential (RGP) was evaluated. Undercutting (June) had the largest effect on the rate of shoot growth. Wrenching in July reduced the rate of shoot elongation further, wrenching in August had a smaller effect, while wrenching in October had no effect. Treatments had little effect on the date of growth cessation in the year of treatment or date of bud flushing the following spring. Wrenching had little effect on root collar diameter, but improved (reduced) sturdiness (height/diameter), especially if carried out late in the season and/or more than once. Wrenching also increased RGP, decreased height and improved (decreased) the shoot:root ratio, but had a small or non-consistent effect on shoot and root dry weights. Except for final height, the time of wrenching had a small effect on this outcome. The results of this study suggest that larch transplants should be undercut in June and wrenched early if height control is required, but more than one wrenching may be necessary to improve RGP.