Reclamation of intensively managed soils in temperate regions by addition of wood bottom ash containing charcoal: SOM composition and microbial functional diversity

Abstract

Wood bottom ash (BA), a complex mixture of mineral ash and moderate amounts of charcoal, can be used as a fertilizer in agricultural and forestry systems. BA is generated as a by-product of biomass combustion and may become a major source of pyrogenic organic matter (OM) as a result of the current high demand for biomass energy. However, very few studies have investigated how the application of BA to land affects soil organic matter (SOM) quality and soil biological properties.In the present study, changes in soil microbial community and community level physiological profile were related to changes in SOM composition (element analysis and 13C CP–MAS NMR) and thermal stability (DSC). The parameters were monitored throughout 3 years in a field experiment in which a degraded soil (acidic, poorly drained and low SOM content) was treated with different doses (16 and 32Mgha−1) of each of two types of BA (fly ash and mixed ash). The treatments led to changes in SOM composition that affected soil microbial communities. The data suggest that some of the pyrogenic OM in the BA may have been mineralized by soil microorganisms. The relatively low recalcitrance of the charcoal, as well as the priming effect of labile organic compounds and the higher nutrient availability may have favoured the process. Although application of BA to land may be useful for restoring fertility and the C-sequestration capacity of soil, the charcoal contained in this type of ash may be susceptible to microbial degradation in humid temperate climate zones and is not stable in the long term.