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Ethanol-soluble and insoluble fractions of humic substances in soil fulvic acids

Soil Science & Plant Nutrition 38(3): 391-399

Ethanol-soluble and insoluble fractions of humic substances in soil fulvic acids

Humic substances in fulvic acids (FAs) obtained as polyvinylpyrrolidone (PVP)-adsorbed fractions were further fractionated based on their solubility in ethanol. Elementary composition, IR spectra, UV-Vis spectra, saccharide contents, molecular size distribution, and 13C-NMR spectra were clearly different between the ethanol-soluble and the insoluble fractions. The yield of the ethanol-soluble fractions exceeded 80%. These fractions showed higher aromatic- and carbonyl-C contents than the insoluble fractions. The differences in the signal intensities of phenol or aryl ether C-1 and methoxyl groups in the 13C-NMR spectra (lowland paddy soil gt brown forest soil gt ando soil) as well as the aromatic-C contents (lowland paddy soil gt ando soil gt brown forest soil) of these fractions among the three soils suggested that the content and composition of the aromatic components varied depending on the soil types. Saccharides and nitrogen compounds were mainly distributed in the ethanol-insoluble fractions and it was suggested that these fractions were composed of humic substances combined with polysaccharides. The weight average molecular weights of these fractions which were 25,000-30,000, were about two times as large as those of the ethanol-soluble fractions. The lower DELTA-log K values of the insoluble fractions than those of the soluble fractions indicated the presence of structural differences in the aromatic components between the two fractions.

Accession: 002373632

DOI: 10.1080/00380768.1992.10415071

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