Soil Chemical Properties Following Wood Ash Applications after Biomass Harvesting in the Boreal Forest.

Forest land application of wood ash could improve soil fertility, divert materials from landfills and close a loop in the cycling of nutrients in managed forest systems. However, before widespread use of ash as a soil amendment is approved in forest management it must be demonstrated that its use is beneficial to forest soil properties and processes. Concerns regarding an increase in energy production from woody biomass are the costs of ash storage, disposal and usage and these challenges can affect the deployment of forest bioenergy as a renewable energy supply.

The impact of biomass boiler ash applied to full-tree harvested plots on soil chemical properties was determined with repeated soil sampling 1, 2 and 3 years post-ash applications. The site was a boreal jack pine forest in north-eastern Ontario, Canada with coarse textured soils, developed in a deep glaciofluvial deposit with a 10 cm thick forest floor. Bottom ash was applied at four different rates calculated in relation to the harvest removal of calcium, which was estimated at 100 kg Ca ha^-1, with application rates of 400, 200, 100 and 50 kg Ca ha^-1 (equivalent to 5.6, 2.8, 1.4, and 0.7 Mg dry ash ha^-1). The ash applied had a pH of 10.2 and a C concentration of 18.5% by loss on ignition. Our objective was to examine the impact of wood ash on organic and mineral soil acidity, total C and N, exchangeable base cations, base saturation and cation exchange capacity.