IMPACTS OF SURFACE APPLIED ALKALINE-TREATED BIOSOLIDS ON SPRUCE PLANTATION SOILS AND VEGETATION IN NOVA SCOTIA, CANADA

Abstract

Decades of acid deposition in northeastern North America has resulted in base cation (Ca, Mg, K) loss and increased exchangeable Al concentrations in many forest soils across the region. In Nova Scotia, Ca has been identified as a potentially limiting nutrient affecting current or future forest productivity in many areas – including plantation sites where nutrient demands are increased through intensive management. In this study, the use of alkaline-treated biosolids (ATB) on spruce plantations was investigated. It was hypothesized that ATB could be a good source of Ca in Ca-limited sites, while providing an environmentally sound end-use for this waste-stream product.

Through field and greenhouse trials, it was found that ATB can increase mineral soil Ca and base cation / Al ratios in Ca-limited sites, while also increasing forest floor pH and reducing exchangeable Al3+ concentrations. In addition, ATB treatments did not result in any significant accumulation and/or leaching of NO3- or trace metals, nor to any impact on ground vegetation abundance or diversity in the juvenile plantations assessed. It did, however, improve Ca, K, P, and Mn concentrations in white spruce crop tree foliage, while also slightly increasing diameter increment over two growing seasons.

With appropriate consideration of soil and site characteristics, use of ATB could be an effective way to offset current or future Ca deficits associated with base cation depletion and intensive harvesting in Nova Scotia spruce plantations, but it may not result in any short-term increases in yield due to lack of significant impact on N availability and/or the presence of other limiting nutrients. In addition, ATB produced using cement kiln dust as the alkaline stabilizer is a poor source of Mg, and the possibility of creating major Ca:Mg imbalances and/or inducing Mg shortages needs to be addressed when applying ATB to plantation soils.

Although initial results support the possible use of ATB in spruce plantation nutrient management, further research is needed to assess the longevity of ATB treatment impacts on plantation soils and vegetation, as well as the associated cost-effectiveness of ATB use versus other amendments such as lime and wood ash.