Effects of planting orientation and density on the soil solution chemistry and growth of willow cuttings

Short rotation coppice (SRC) willow are established conventionally by inserting cuttings vertically into the soil, but their ability to reproduce vegetative has also been demonstrated by planting cuttings horizontally. There is a lack of knowledge about the biomass production, root characteristic, and nutrient leaching of plantations established through horizontally planted cuttings. A plot experiment was conducted to compare the soil solution chemistry and the growth of stem and roots of willow cuttings (Salix schwerinii) with vertical or horizontal planting orientation at two planting densities (corresponding to 7500 and 22,500 cuttings ha−1). The horizontally planted cuttings achieved the same stem yields (4.08 t ha−1) as the vertically planted cuttings (4.86 t ha−1). The stem biomass was doubled to a planting density of 22,500 cuttings ha−1 (6.34 t ha−1) compared to at 7500 cuttings ha−1 (3.36 t ha−1). The effect of planting orientation or density had no effect on the root biomass or production. Willows decreased the conductivity, (NO2+NO3)–N and the dissolved total N in the soil solution compared with unplanted plots, but the influence was not detected systematically at each sampling depth or in each year. The differences in soil water concentrations between planting treatments remained small. In conclusion, we have shown that both planting orientation methods, horizontal and vertical, can be used for preventing nutrient leaching and maximizing biomass production. It will also be interesting to expand the application of horizontally planted willow materials in order to stabilize slops, control erosion and reclaim contaminated sites.

► The yield is not different between the vertical and horizontal planting orientations.
► Planting density only affects on the stem biomass, not root biomass.
► The horizontal planting orientation can be used in biomass and nutrient leaching.