Geoscience Reference
In-Depth Information
Fig. 18.31 FTIR spectra of fulvic acid (FA) indicating the structural differences induced by soil
acidification. NS natural soil, AS acidified soil (modified after Calace et al.
2001
). Reprinted from
Calace et al. (
2001
). Copyright 2001 with permission from Elsevier
podzolization process. Mulder et al. (
1989
) concluded that ''…the current rapid
depletion of organic aluminum in the rooting zone of many acid sandy soils is
irreversible on a time scale of decades or centuries.''
Acid rains also may affect the molecular configuration and the properties of soil
humic compounds. Calace et al. (
2001
) reported a laboratory experiment in which
humic and fulvic acids extracted from a natural soil were subjected to simulated
acid rains, until a soil pH of 4 was obtained. The effect of soil acidification on the
humic and fulvic substances was determined in terms of humic/fulvic substance
molecular weight and composition of the soil, before and after soil treatment.
Neither molecular weight nor the FTIR spectrum of humic acid was influenced by
the acidification process. In contrast, both the molecular weight and the FTIR
spectrum of the fulvic acid were affected. The differences between FTIR spectra of
pristine and acidified fulvic acids with molecular weights of 50 and 3 kDa,
respectively, are shown in Fig.
18.31
.
The fulvic acids extracted from the pristine soil (FA-NS) reveal a greater alcohol
and carbohydrate content (1,050-1,250 cm
-1
) and higher adsorption than the
