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A pooled sample of sun-dried Oedogoniumwas made from equalparts biomass from four successive harvests in June 2013. Thebiomass was converted to biochar through slow pyrolysis at fivedifferent highest heating temperatures (HHT; 300, 450, 600, 750and 900 C). Each of the biochar samples were produced byweighing 150 g of Oedogonium into a ceramic bag which was putinto a muffle furnace purged with N2 gas (4 L min1). The biomasswas left at the HHT for 60 min, then removed and cooled to roomtemperature under continued N2 flow and re-weighed to calculateyield.The elemental profile (C, H, O, N, and S) of the biomass andbiochar were analysed using an elemental analyser (OEA LaboratoryLtd, United Kingdom). Metal concentrations in the biomassand biochar samples were measured as described above. The O:Cratio was calculated from the ultimate analysis to predict the longtermstability of biochar C (Crombie et al., 2013; Spokas, 2010).Electrical conductivity (EC) and pH were determined in 10:1 waterand sample mixtures (Rayment and Higginson, 1992). Exchangeablemetals were eluted from biomass and biochar according tostandard protocols (Farrell et al., 2013). Briefly, the biomass andbiochar samples were sieved (0.5e4.0 mm), then added to deionized(DI) water (1:10 w/v) and placed in a shaker incubator cabinet(100 rpm, 20 C) for 24 h (British Standards, 2002). The watersamples were then filtered (0.45 mm) and analysed for metals (As,Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Na, Ni, Pb, Se and Zn) as described. Allplastic-ware was acid washed before use (5% HNO3, 48 h).
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