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

Abstract

Abstract The non-humic substances in fulvic acids (FAs) of three Japanese soils were obtained as the non-adsorbed fraction through a column of insoluble polyvinyl-pyrrolidone (PVP), and this fraction was further fractionated based on the solubility in ethanol. Although the yield of the ethanol-soluble fractions from the PVP-non-adsorbed FAs was 5–7%, the analytical data indicated that their chemical structure was clearly different from that of the ethanol-insoluble fractions. The ethanol-soluble fractions were characterized by low average molecular weights, low saccharide contents and strong peaks for aliphatic C-H, alcoholic C-O, and carboxyl groups in the IR spectra. The 13C-NMR spectrum of this fraction in the ando soil that was determined quantitatively also showed strong peaks for the long alkyl chain, secondary alcohol or aliphatic ether, and carboxyl groups. The main constituents of the ethanol-insoluble fractions consisted of polysaccharides. Contents and composition of saccharides, however, varied depending on the soil types. Pentose content of the insoluble fraction was very high in the lowland paddy soil, and the uronic acid content was higher in the ando soil than in the other two soils. The carbohydrate-C content of the insoluble fractions estimated from 13C-NMK spectra was in the order of lowland paddy soil, ando soil, and brown forest soil. The aliphatic-C content was in the opposite order. These findings suggested that abundant plant components remained in the FA of the lowland paddy soil while many aliphatic components were incorporated into the FA of the brown forest soil.