Characterisation of fulvic and humic acids from leaves of Eucalyptus camaldulensis and from decomposed hay

Soluble soil organic components including fulvic acid (FA) and humic acid (HA) have the ability to complex cations, such as plant toxic monomeric aluminium (Al). We describe the chemistry of FA and HA extracted from two sources before their use in solution culture experiments aimed at determining their ability to ameliorate Al toxicity. Aqueous extracts containing FA and HA were obtained from aerobically incubated leaves of Eucalyptus camaldulensis (Eucalyptus) and decomposed grass and lucerne hay (Compost). The FA and HA were separated and concentrated by precipitation and ion adsorption using XAD-7 resin, purified and dried. Selected elemental properties, size exclusion chromatograms and solid state 13C-NMR spectra obtained for the FA and HA from both sources showed distinct structural differences. The FA obtained from the extensively decomposed Compost consisted of simpler and smaller components. The younger FA and HA obtained from the freshly prepared extract of Eucalyptus were very similar in their chemical attributes.