Fractionation of soil fulvic acids using polyvinyl -pyrrolidone and their lonization difference spectra

Abstract

Fulvic acids were divided into adsorbed brown fractions and non-adsorbed. pale-yellow fractions using insoluble polyvinylpyrrolidone (PVP) as an adsorbent. The distribution pattern of the two fractions varied with the types of soils. The yield of the PVP-adsorbed fraction was higher in the order of brown forest soils, ando soils, and lowland paddy soils and red-yellow soils. The difference spectra between pH 12 and pH 7 (ΔE _7-12 spectra) and those between pH 7 and pH 3 (ΔE ^3-7 spectra) of the PVP-adsorbed fractions were classified into three types corresponding to the types of soils. The ΔE _7-12 spectra of the PVP-adsorbed fractions and humic acids obtained from the same soil were similar. In the PVP-non-adsorbed fractions, both the ΔE _7-12 and ΔE _3-7 spectra did not clearly differ among all soils.