Short-term effects of hardened wood ash and nitrogen fertilisation in a Norway spruce forest on soil solution chemistry and humus chemistry studied with different extraction methods

A field trial with wood ash, nitrogen fertiliser, combined wood ash and nitrogen treatment and control was set up in a Norway spruce [Picea abies (L.) Karst.] forest, and post-treatment changes and differences in humus chemistry and soil solution chemistry at 40 cm depth were studied from 2013 to 2015. Element concentrations in humus samples were compared using NH₄NO₃ extraction (M1) and nitric acid/perchloric acid digestion (M2). Nitrogen treatment led to significant increases in Mg determined after both M1 and M2. No significant effect of ash or ash + nitrogen treatment on soil C or N in the humus layer was found, while pH and concentrations of many elements after M2 increased in the same samples. Decreases after ash treatment for Al, Co, Fe, Ni, Pb and Zn in humus determined after M1 may be because of decreased mobility due to increased pH. Differences depending on analytical method suggest that methodology should be taken into account when evaluating ecological relevance of differences in element concentrations. In soil solution at 40 cm depth nitrogen treatment led to short-term increases in concentrations of , , Ca, Mg, Co, Ni and Zn and a reduction in pH, while ash treatment led to no clear effects.