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Title: CARBON DYNAMICS OF SOIL CLAY-HUMIC COMPLEXES

Author
item Laird, David
item GONZALEZ, JAVIER - IOWA STATE UNIVERSITY
item HILL, RONALD - EXXONMOBIL
item YLAGAN, ROBERT - EXXON PROD. RESEARCH CO.

Submitted to: Clay Minerals Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/18/2001
Publication Date: 6/18/2001
Citation: LAIRD, D.A., GONZALEZ, J., HILL, R.J., YLAGAN, R. CARBON DYNAMICS OF SOIL CLAY-HUMIC COMPLEXES. CLAY MINERALS SOCIETY MEETING. 2001. ABSTRACT P. 29.

Interpretive Summary:

Technical Abstract: Clay-humic complexes have a large influence on the ability of soils to supply water, nutrients, and air to growing plants and are both a sink and a source of greenhouse gasses for the atmosphere. We investigated both the nature of soil clay humic complexes and the turnover rate of carbon in soil clay-humic complexes. Coarse (0.2 to 2.0 um), medium (0.02 to 0.2 um), and fine(<0.02 um)particle size fractions were isolated from 6 different soils using a sonication-centrifugation-decantation technique designed to separate mineralogically distinct fractions. Chemical and XRD analyses indicated that the coarse clay fractions were dominated by quartz with lesser amounts of feldspar, kaolinite and 10 A-illite. The fine clay fractions were dominated by smectite and randomly interstratified I/S. All fractions contained between 30 and 80 g/kg organic C and 0.15 to 0.70 g/kg organic N. Chemical, 13C MAS-NMR, thermol, and SEM analyses indicate the existence of two distinct phases of humic materials in the soil clays. In fine clay separates, humic materials exist as diffuse low density material on basal surfaces of smectites and interstratified I/S. The fine clay fractions are enriched in aliphatic C and have a relatively low C:N ratio(8 to 15). Incubations, 14C-dating, and 14C-labeled residue decomposition studies indicate that C in the fine clay separates is both young (14C dating indicates 101.0 to 106.6% modern C relative to a 1950 oxalic acid standard) and biologically active. By contrast, the organic C in coarse clay separates is present in discrete high density particles with relatively high C:N ratios(17 to 26). The C associated with the coarse clay separates is both old(14C dates are 60 to 670 y.b.p.)and biologically unavailable.