Properties of non-humic substances of fulvic acids fractionated by ethanol precipitation

Abstract

Abstract The PVP-non-adsorbed fulvic acids (FAs), which are non-humic substance fractions of FAs, were fractionated by precipitation from an aqueous solution upon gradual addition of ethanol. The amount of precipitate increased exponentially with the increase of the ethanol concentration, and one-third of these fractions was soluble in a 90 × 10-2 L L-1 ethanol solution. The characteristics of the fractions suggested that the non-humic substances of FAs consisted of a variety of materials differing in their chemical composition and molecular size. Saccharide contents, elementary composition and IR spectra indicated that the contents of aliphatic chains and carboxyl groups as well as the degree of unsaturation were higher in the fractions precipitated at a higher ethanol concentration. The reverse was true for the contents of saccharides and peptides as well as the molecular size distribution. Differences in the saccharide contents and IR spectra among the sub-fractions were most conspicuous in the samples obtained from the brown forest soil, while they were attenuated in the samples from the lowland paddy soil. However, the elementary composition and molecular size distribution were also clearly different in the sub-fractions from the lowland paddy soil.