Soil Water Responses to Wood Ash Addition to Acidic Upland Soils: Implications for Combatting Calcium Decline in Lakes

Calcium (Ca) concentrations in lakes have declined in many regions, and concerns have been expressed that Ca levels are falling below biologically significant thresholds. Wood ash additions to soil are typically used to combat soil acidification, and it is unclear whether wood ash additions to upland soils will lead to higher Ca leaching to surface waters. In this study we applied fly ash or bottom ash at 4 Mg ha−1 and 8 Mg ha−1 to upland soils at replicated plots in Haliburton Forest in central Ontario and measured soil water chemistry at 3 depths over 4 years. Increases in soil water Ca concentration following application were quite modest and occurred primarily in the fly ash treatments in the upper depth (0.3 m) during the first 2 years following application. There was no concomitant increase in pH or acid-neutralizing capacity primarily because of the high sulphate leaching associated with the fly ash treatments. Overall, these results show that wood ash addition to soils at moderate doses will have little impact on soil export to lakes.