Macronutrients, metals, and metalloid concentrations in non-industrial wood ash in relation to provincial land application limits in Ontario, Canada

Abstract

Non-industrial wood ash (NIWA) provided by residents who heat with wood, is rich in base-cations and other nutrients and may be used as a forest soil amendment to return nutrients lost through acid deposition. However, due to concerns regarding high trace metal concentrations, most wood ash is landfilled in Canada. This study investigated the chemical variability of NIWA of individual samples and homogenized mixtures to determine if they met Ontario provincial trace metal restriction limits. One hundred and seven ash and 10 charcoal samples collected from residents of Muskoka, Ontario, and three 10-sample composites were analyzed. Chemical composition varied among individual samples, but nutrient levels were within or higher than reported ranges for industrial wood ash, while trace metal values were lower. Ninety-seven percent (104 of 107) of the samples were within Ontario Regulation 267/03 of the Nutrient Management Act, and after homogenization, all samples were below soil application restriction limits. This study indicates that NIWA can be safely used as a forest soil amendment but recommends routine testing of batch samples prior to application.