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United States Department of Agriculture

Agricultural Research Service


item Clapp, Charles
item Hayes, Michael

Submitted to: International Humic Substances Society Conference
Publication Type: Proceedings
Publication Acceptance Date: 7/1/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Organic matter in soils is composed of an intimate combination of organic and inorganic components. The mineral (inorganic) fraction is usually clay or gel-like material that provides a backbone for the humus (organic) fraction. The organic matter provides the more reactive network for water, air, and nutrient interaction in the soil. It is necessary to extract by different methods and identify the individual components of the organic matter, such as the humic substances--humic acid, fulvic acid, and humin-- and the polysaccharides. These fractions are especially important because they are the most active agents for binding soil particles (aggregation) and for transporting chemical pollutants (pesticides). By isolating, fractionating, and characterizing these components, we are able to uncover the processes by which they carry out their activities. Understanding their modes of action will allow us to find ways of preventing undesirable chemicals from polluting the soil and ground water. In turn, the environmental quality of agricultural ecosystems will be preserved.

Technical Abstract: An agricultural soil (Mollisol), amended with 200 kg ha**-1 yr**-1 of N [as **15N-enriched (NH4)2SO4] for the 8 previous years, and which had carried a maize (Zea mays L.) crop for that period, was extracted exhaustively with the following sequence of solvents: sodium pyrophosphate (Pyro, 0.1M) at pH 7.0; Pyro (0.1M) at pH 10.6; Pyro (0.1M) and NaOH (0.1M) at pH 12.6; NaOH (0.1M) at pH 12.6; and dimethyl sulfoxide (DMSO) + HCl (12M) in a ratio of 94:6. Increases in the basicities of the extractants increased the extent to which the soil organic components were solubilized, and the introduction of NaOH into the solvent systems significantly increased the extractabilities of the sugar- and amino acid-containing components in the humic acid fractions. Humic substances isolated in DMSO/HCl, when separated from the solvent system, did not display any of the solubility characteristics of operationally-defined humin, and had solubility properties that were more characteristic of fulvic acids than humic acids or humin.

Last Modified: 06/23/2017
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