High biomass productivity of short-rotationwillow plantation in boreal hokkaido achieved by mulching and cutback

Abstract

Weed control, which is commonly achieved by herbicides, is important in successfully establishing short-rotation coppice (SRC) of willow. In this study, we examined agricultural mulch film as a means of effective weed control and the influence of cutback practice (coppicing the first year's shoot growth in the winter following planting) on biomass production in boreal Hokkaido, Japan. One-year-old cuttings from two clones each of Salix pet-susu and S. sachalinensis were planted in double-rows at a density of 20,000 plants ha-1. All plants were harvested three growing seasons after cutback. Average oven-dried biomass yield was 5.67 t ha-1 yr-1 with mulching, whereas it was 0.46 t ha-1 yr-1 in the unmulched control with a weed biomass of 4.13 t ha-1 yr-1, indicating that mulching was an effective weed control. However, weeds grew vigorously on the ground between mulch sheets and their dry biomass amounted to 0.87 t ha-1 yr-1. Further weeding between the mulch sheets enhanced the willow biomass yield to 10.70 t ha-1 yr-1 in the treatment with cutback. In contrast, cutback even reduced the willow yield when there were weeds between the mulch sheets. This negative effect of cutback on the willow yield resulted from nutrient competition with weeds; there was similar leaf nitrogen content and dry biomass per unit land area for the weeds and willows combined in the control and mulching treatments. These results suggest that growing SRC willow is feasible in boreal Hokkaido if combined with complete weed control and cutback, and is facilitated by using mulch film.