The organic matter extracted from peats (P), leonardites (Le) and lignites (Li) was characterised by humification parameters and electrofocusing (EF). The degree of humification and the humification index might be used to distinguish P from Le and Li, but not Le from Li because they showed overlapped values, while the humification rate could be used only for the identification of Le and EF profiles of P, Le and Li fertilisers revealed different band patterns: P samples did not show bands in the region with isoelectric point, pI > 4:4; Le samples showed very intense bands in the region with pI > 4:4; Li samples showed a very different band pattern with poorly resolved bands in the region with pI > 3:8. P, Le and Li samples can be distinguished by combining humification parameters and EF.

Introduction

The chemical characterisation of the organic matter extracted from peats (P), leonardites (Le) and lignites (Li) is difficult because of the complexity of humic substances (HS) and the great heterogeneity of the materials. Organic matter from these materials containing a high amount of HS has been characterised using spectroscopic techniques, such as laser fluorescence (Morita and Measures, 1983), ¹³ C-NMR (US Geological Survey, 1989), ¹H-NMR (US Geological Survey, 1989), FT-IR (Francioso et al., 1996, 1998), surface enhanced Raman spectroscopy (Sanchez-Cortez et al., 1998). However, it usually happens for the HS from different origins, that these techniques show some difficulties in characterising the organic matter. Ciavatta et al. (1989) proposed the use of two humification parameters, the degree of humification (DH) and the humification rate (HR), to evaluate the humification level in organic materials. Since then, DH and HR have been applied to several organic materials, such as soils (Govi et al., 1992), slurries (Govi et al., 1989), compost (De Nobili et al., 1989; Ciavatta et al., 1992; Govi et al., 1993b), and sludges (Govi et al., 1993a). Humification parameters have also been applied to characterise organic and organic-mineral fertilisers (Ciavatta et al., 1989, 1996; Govi et al., 1989; Alianiello et al., 1999) and appeared to be useful for the differentiation of P from Le samples, but not for their humic extracts (HE) (Ciavatta et al., 1996). De Nobili et al. (1985) proposed the use of gel electrofocusing (EF), as a qualitative parameter to characterise HS of different origins and to evaluate the humification level of an organic material from a qualitative point of view. Govi et al. (1992) showed that the EF technique was useful for evaluation of differences in soil organic matter not detectable by quantitative parameters such as DH and HR.

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