[Structural-functional characteristics of humic substances from podzolic and bog-podzoloic soils]
2007
Lodygin, E.D. | Beznosikov, V.A. | Chiukov, S.N.
The middle taiga soils developed in covering loamy deposits in the Russian European Northeast were studied. The following functional groups are identified by the use of NMR and EPR spectroscopy: carboxyl, carbonyl, aliphatics, phenol, quinine and aromatic. Macromolecules of humic acids (HA) contain significant amounts (up to 44.6%) of frame-forming aromatic fragments with a small share of carbohydrates. The carbonic carcass of fulvic acids (FA) is dominated by aliphatic chains, carbohydrates and amino acids (up to 77.8% in total). This explains their high solubility and low hydrophobicity. Cultivation of podzoloc soils reduces carboxyl groups in HA content and increases aromatic fragments that promotes HA accumulation in arable horizons. HA of podzolic soils are enrich of stable oxygen-containing compounds and the FA are enrich in less oxidezed ones. HA contain 3 fractions differing in molecular masses: more than 150 kDA, 73-80 and 13-23 kDA; FA contain more than 5 and 1-2 kDA. HA contain 1.5-5 times more free radicals as compared to FA. The content decreases downward soil profile. HA has high potential for polymerization and complexation following by the radical mechanism. Cultivation reduce the paramagnetic activity of humic compounds by more than 20% as compared to their virgin analogues; in result more humified and more bio-thermodynamically stable compounds in arable horizons are accumulated. Podzolic surface-gley soils are more resistant to man-caused loads as compared to podzolic and gley-podzolic ones. Aliphatic fat acids and their ethers constitute the lipid fraction of soil humus. The increase of soil moistening leads to increased share of non-saturated components. The express method of pK-spectrocsopy is recommended to assess acid-base properties of FA. By this method carboxyl and phenol classes of ionogenic groups into sub-classes with similar dissociation constant values (pK 2.9-3.8, 5.0-5.8, 6.8-8.0 and 9.6-10.5) were divided. The results of NMR and pK-spectroscopy have the closely correlation (r=0.74, P=0.95)
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