Initial effects of wood ash application to soil and soil solution chemistry in a small, boreal catchment

With the conception that whole tree harvesting leads to an impoverishment of forest soils wood ash application is recommended, with the foremost benefits being increased pH in soil and subsequent surface waters, and recycling of nutrients from the wood ash.In this investigation a small boreal catchment in central Sweden was studied for 2 years before and 2 years after treatment with the maximum recommended dose, 3 tonnes/ha, of crushed, self-hardened wood ash. The sampling area was situated in a slope towards a stream, to include the effect on both recharge- and discharge areas with different soil constitutions. The soil solution chemistry, exchangeable pool of cations and potential heavy metal accumulation in berries were studied. Temporary increases in soil solution concentration were found for K in the recharge area and Ca and SO4 in the discharge area when comparing ashed and control areas. No change in exchangeable cations was observed during the study period, and no increase of heavy metals in bilberries did occur. These small changes in the constitution of the soil solution do not suggest wood ash application as a method to improve soil quality in an initial phase.

► A forested catchment was monitored during 4 years to study the initial effects of wood ash application (WAA) (3 tonnes/ha).
► Overall the WAA had a modest impact on the soil solution chemistry compared to seasonal variation.
► Significant increases of K and Ca were though registered for the ash treated area.
► No effects were detected in the soil respiration rates, and in the metal content of bilberries.