Wood/sludge ash effects on white spruce seedling growth

The disposal of wood ash and/or pulp and paper mill sludges is becoming increasingly more challenging as landfills are more difficult to site due to diminishing land availability and public opposition, as well as more costly to construct and operate because of increasingly stringent regulations. The most notable alternative to disposal that is receiving the attention of the forest industry is land application. The objective of this study, therefore, was to determine the influence of applying a pulp mill wood/sludge ash mixture on 1) various soil chemical properties of an Orthic Gray Luvisol and 2) the growth and nutrient uptake of white spruce [Picea glauca (Moench) Voss] seedlings. The pulp mill wood/sludge ash mixture from an olivine burner was surface broadcast at rates of 1 and 5 Mg ha -1 around white spruce seedlings planted on disc-trenched microsites. Soil solutions from lysimeters and soil samples were analyzed for exchangeable elements, soil pH and electrical conductivity while white spruce tissue samples were analyzed for various elements. Applications of pulp mill wood/sludge ash material significantly increased the soil pH from 4.8 to 6.9, resulting in increased soil extractable and soil solution P, Ca, and Mg. Soil electrical conductivity (EC) was increased from about 0.02 dS m -1 to approximately 0.10 dS m -1 by the heavier application rate of ash. In addition, at higher ash application rates, white spruce seedling growth was significantly decreased, suggesting salt phytotoxicity effects from the ash. These results indicate that with proper rate determination and management of salt effects, land application of this material would not appear to pose serious problems for white spruce seedling establishment. Key words: Picea glauca, wood/sludge ash, Luvisols, lysimeters, electrical conductivity, pH