[Fractionation and spectroscopic property of dissolved organic matters in soils]

Based on a modified Leenheer DOM fractionation sche me, fractionation of DOM from paddy soils was conducted byusing XAD-8 resin into hydrophobic bases (HOB), hydrophobic acids (HOA), acid-insoluble matter (AIM), hydrophobic neutrals (HON) and hydrophillic matter (HIM), and their structural characteristics were studied by means of elemental composition, FTIR and 1H-NMR spectroscopy. The fractionation scheme used here provided a preferable separation of the fractions in terms of hydrophobicity and a high recovery. Of the DOC extracted from the soils, the HOB was the least fraction, accounting for 0.73%-3.83%, and the HIM fraction was the largest, accounting for 36%-42%. The HON fraction represented 7%-15%. The relative content of the HOA plus AIM was about 50%. Separated by this technique, the large-chain alkylate and the major portion of the N components mainly characterized HON, while the HOA fraction contained a large amount of carboxyl groups but less amount of aromatic groups with a higher quantity of carbohydrates compared to that of FA. AIM fraction was dominated by high branched (n value) polyphenols and humus bound carbohydrates. HIM was characterized by considerable amount of carboxyl and carbohydrates.