Long-term effects of ash and N fertilization on stand growth, tree nutrient status and soil chemistry in a Scots pine stand

The long-term effects of varying quantities and types of ash, given together with nitrogen, on stand growth, tree nutrient status and soil chemical properties were studied in a Scots pine (Pinus sylvestris) stand on upland soil. The treatments were: unfertilized control (C), nitrogen (N), wood ash and nitrogen (WA + N), bark ash and nitrogen (BA + N) and peat ash and nitrogen (PA + N). The dose of nitrogen was similar (185 kg N ha−1 as urea) in all the fertilizer treatments. The ash doses were 1, 2.5 and 5 t ha−1. Urea was applied in autumn 1978, and ash in March 1979. The C and N treatments had six replicates, and the other treatments two.The amount of elements added in wood ash far exceeded those added in equivalent amounts of bark or peat ash. The resulting differences in soil chemical properties were mainly due to the amount of base cations added in the ash and not to the ash type. Only the treatment with the highest dose of wood ash produced significant changes in most of the soil chemical properties. The increase in humus layer pH given by this treatment was 2.1 pH units after 9 growing seasons, and 0.9 pH units after 23 growing seasons. The concentration of extractable Ca was six- and three-fold compared to the control after 9 and 23 growing seasons, respectively.There was a positive volume growth response to N added either alone or together with various types and doses of ash, during the first two periods (1978–1982 and 1983–1987) after the treatments. No positive response to the N treatment was subsequently detected. In contrast, during the third study period (1988–1998) 2.5 t ha−1 of wood ash given together with N resulted in a significantly higher volume growth than the control or N alone. A corresponding positive, although non-significant, growth response was also obtained with the other doses of wood ash and the highest dose of bark ash.