The effect of wood ash (0, 6, 12, and 24 t ha^-1) on the nutrient concentrations and biomass production of willows (Salix viminalis and S. x dasyclados) and birches (Betula pendula and B. pubescens) on two cutaway peats was studied in greenhouse conditions. In addition to ash, all treatments included fertilisation with nitrogen (150 kg N ha^-1). The largest amount of wood ash increased the pH from 4.0 to 7.3 for Aitoneva peat and from 5.0 to 7.5 for Piipsanneva peat. Increasing the amount of ash also significantly increased extractable phosphorus, potassium, calcium, and magnesium concentrations in peat – even the smallest dose increased concentrations manifold compared to unfertilised peats. The growth of the studied species was affected by both peat type and fertilisation treatment. Unfertilised willows and willows fertilised with nitrogen died in Aitoneva peat and grew poorly in Piipsanneva peat. Biomass production of birches in unfertilised peat was low. Nitrogen fertilisation without ash did not increase growth. The best growth was recorded with the lowest dose of ash (6 t ha^-1). Ash fertilisation significantly increased the foliar concentrations of phosphorus and potassium in all species studied and decreased those of calcium and magnesium. The study indicated that the original peat characteristics affect growth of seedlings even when the sites are fertilised. Wood ash proved to be a suitable fertiliser in afforestation of cutaway peatlands.

Keywords: willow, birch, cutaway peatland, wood ash, fertilisation, biomass production.