Effect of wood ash fertilization on soil chemical properties and stand nutrient status and growth of some coniferous stands in Finland

The effects of wood ash or wood ash plus nitrogen (N) fertilization on soil chemical properties, needle nutrient concentrations and tree growth were studied in five coniferous stands, aged 31-75 yrs, after 5 and 10 yrs. In each experiment 3 t ha −1 of loose wood ash was applied to three replicated plots (30×30 m). In three of the experiments 120-150 kg N ha −1 was applied together with the same wood ash (WAN). These three experiments also included a stand-specific fertilization (SSF) treatment, which consisted of 120, 150 or 180 kg N ha −1 . Five years after wood ash or WAN application the pH increase in the humus layer was 1-1.7 pH-units and in the 0-5 cm mineral soil layer 0.3-0.4 pH-units. The increase was approximately the same 10 yrs after application, and was also associated with an increase in pH in the 5-10 cm mineral soil layer. Wood ash or WAN significantly increased both the total and extractable calcium and magnesium concentrations in the humus layer on all the sites. Wood ash or WAN had an increasing effect on the boron concentrations, but a decreasing effect on the manganese concentrations in the needles. Wood ash had no significant effect on the volume growth. The trees on the WAN plots grew as well as or slightly better than those on the SSF plots.