Cation exchange capacity of density fractions from paired conifer/grassland soils |
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Authors: | Sarah I Beldin Bruce A Caldwell Phillip Sollins Elizabeth W Sulzman Kate Lajtha Susan E Crow |
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Institution: | (1) Department of Crop and Soil Science, Ag and Life Science 3017, Oregon State University, Corvallis, OR 97331, USA;(2) Department of Forest Science, Oregon State University, Corvallis, OR, USA;(3) Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USA |
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Abstract: | The cation exchange capacity (CEC) of a soil depends on the type and amount of both mineral and organic surfaces. Previous
studies that have sought to determine the relative contribution of organic matter to total soil CEC have not addressed differences
in soil organic matter (SOM) composition that could lead to differences in CEC. The objectives of this study were (1) to compare
the CEC of two distinct SOM pools, the “light fraction (LF)” composed of particulate plant, animal, and microbial debris,
and the “heavy fraction (HF)” composed of mineral-bound organic matter; and (2) to examine the effects of differences in aboveground
vegetation on CEC. Soil samples were collected from four paired grassland/conifer sites within a single forested area and
density fractionated. LF CEC was higher in conifer soils than in grassland soils, but there was no evidence of an effect of
vegetation on CEC for the HF or bulk soil. LF CEC (but not HF CEC) correlated well with the C concentration in the fraction.
The mean CEC of both fractions (per kg fraction) exceeded that of the bulk soil; thus, when the LF and HF CEC were combined
mathematically by weighting values for each fraction in proportion to dry mass, the resulting value was nearly twice the measured
CEC of bulk soil. On a whole soil basis, the HF contributed on average 97% of the CEC of the whole soil, although this conclusion
must be tempered given the inflation of CEC values by the density fractionation procedure. |
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Keywords: | Cation exchange capacity Density fractionation Soil organic matter Carbon Light fraction |
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