Forest floor chemistry and mineral soil ion exposure after surface application of alkaline-treated biosolids under two white spruce (Picea glauca) plantations in Nova Scotia, Canada

Two field trials were established to evaluate the use of alkaline-treated biosolids (ATB) to offset current or predicted Ca deficits in Nova Scotia forest soils under juvenile white spruce (Picea glauca) plantations. At the rates applied (7.5 and 15 t ha−1 wet weight), ATB treatments led to significant increases in total and available Ca within the forest floor and surface mineral soil, significant increases in forest floor pH, significant or near-significant decreases in exchangeable forest floor Al3+ concentrations, and negligible leaching of metals (Cu, Cd, Pb, Zn) for the 2-year duration of study. Near-surface PO43−-P availability was also slightly enhanced after an initial delay period. However, despite relatively high K concentrations in the ATB product used, there were no significant increases in forest floor K concentrations, suggesting a relatively rapid release and movement of K+ to deeper soil layers compared to Ca2+. There were also no significant increases in forest floor Mg concentrations, or in total and available N. Results suggest that ATB could be a good source of Ca in Ca-limited sites, but nutrient imbalances may be a problem on sites where K and Mg depletion has also occurred or where N is also limiting.