The impact of amending forest soils with wood ash on soil organic matter attributes and associated properties

Abstract

Wood ash, the byproduct of bioenergy production from biomass, is typically discarded into landfills as waste. Adding ash back to soil may supply nutrients to soil that are lost through biomass harvesting, increase soil pH, and improve site productivity, but the effects on soil organic carbon are not well known. In Canada, there are eight wood ash experiments across the country investigating the effects of ash addition on site productivity. In this study we measured soil carbon concentrations and estimated stores of total soil organic carbon, sand fraction carbon, microbial biomass carbon, hot water extractable carbon and mineralizable carbon in soils collected from these experiments. Analyses of variance (ANOVA) were conducted to determine the significant effect of different rates of wood ash application on each fraction. The difference between ash application rates was analyzed using Tukeys post-hoc test. Following ANOVA, a multivariate analysis was conducted using principal component analysis (PCA) to capture the variables significantly contributing to the total variation in the study. Results revealed that labile fractions were more responsive than the total carbon, but none of the measured attributes showed consistent change across the sites with ash addition. Carbon attributes that varied significantly (p<0.05) with wood ash addition varied across the sites and between the forest floor and mineral soil layers. Wood ash addition had the greatest effect on microbial biomass carbon, hot water extractable carbon and sand sized fraction carbon. There was no detrimental effect of wood ash addition on carbon storage at any site. The effect of ash addition was also dependent on soil texture, soil layers and the application rate. Fractions of soil organic carbon were typically more responsive to ash addition than total carbon and may be included as indicators of soil quality.