Author
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Laird, David |
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Submitted to: Clay Minerals Society Meeting
Publication Type: Abstract Only Publication Acceptance Date: 7/1/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Agricultural soils may help reduce net emissions of greenhouse gasses to the atmosphere through increased C sequestration in soil organic matter. Objectives of this study were to determine the relationship between mineralogy and the chemical and biochemical properties of humic substances associated with soil clay minerals. The soil sample used was from the Ap horizon of a Webster (Typic Haplaquoll) soil. The whole soil clay fraction (<2um size fraction) was separated by a noninvasive sedimentation technique, and coarse, medium, and fine clay fractions (0.2-2.0, 0.02-0.2, and <0.02 um size fractions, respectively) were separated from the whole clay sample by an invasive sonication-centrifugation technique. The samples were analyzed for mineralogy, chemical composition, total C and N, C chemistry, biochemistry, and morphology of the clay-humic complexes. The results indicate that the course clay fraction is dominated by quartz with lesser amounts of kaolinite, 10 A-illite, and feldspars. The medium and fine clay fractions are dominated by smectite and a low-charged interstratified illitic phase. The C:N ratios of humic substances associated with the coarse, medium and fine clay fractions are 17, 10, and 10, respectively. The coarse clay humics have stronger C=O and C-O 13C-NMR peaks and lower NaOH extractable amino acids than humics associated with the fine clay fraction. The results suggest two distinct pathways for the formation of stabilized humic substances; (i) bio-redox reactions leading to the formation of dense metal humic complexes, and (ii) abiotic accumulation and polymerization of humic monomers on surfaces of 2:1 phyllosilicates. |
