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 alum inium (Al). We describe the chemistry of FA and HA extracted from two sourc es before their use in solution culture experiments aimed at determining th eir ability to ameliorate Al toxicity. Aqueous extracts containing FA and H A were obtained from aerobically incubated leaves of Eucalyptus camaldulens is (Eucalyptus) and decomposed grass and lucerne hay (Compost). The FA and HA were separated and concentrated by precipitation and ion adsorption usin g XAD-7 resin, purified and dried. Selected elemental properties, size excl usion chromatograms and solid state C-13-NMR spectra obtained for the FA an d HA from both sources showed distinct structural differences. The FA obtai ned from the extensively decomposed Compost consisted of simpler and smalle r components. The younger FA and HA obtained from the freshly prepared extr act of Eucalyptus were very similar in their chemical attributes. (C) 2000 Elsevier Science Ltd. All rights reserved.