Characterization of the Organic Matter in Wood Ash from Biomass Power Plants in Relation to the Potential Use As Amendments in Agriculture

As a result of the increased demand for bioenergy, wood ash (WA), the main residue generated, may become a major source of pyrogenic organic matter. WA contains organic aromatic structures and could be used in agriculture, in a similar way to biochar, to improve the amount and quality of soil OM (OM). However, the organic composition of WA may differ from that of biochar, which has not yet been addressed. In the present study, different types of fly wood ash (FWA) and mixed wood ash (MWA), generated in industrial boilers, were characterized and compared with biochar generated from different feedstocks and at different temperatures (300 and 600 degrees C). WA differed in the amount and composition of the OM. The OM in MWA consisted of condensed carbon as well as substantial amounts of lightly charred plant biomass. Because of the low degree of carbonization of this OM, it may be susceptible to microbial degradation after application to soil. By contrast, the OM in FWA comprises highly carbonized and condensed organic compounds, similar to those in biochar. Selection of the most suitable type of WA will be determined by the requirements of the specific soils. MWA could be used to amend soils requiring high amounts of OM, whereas FWA might be more appropriate for application in acid soils rich in OM. Thermal analysis proved a useful tool for characterizing the charred material in these by-products in order to determine the best strategy for use of the material in agriculture. Copyright (c) 2017 John Wiley & Sons, Ltd.