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The Effect of Periodate Oxidation on the Strength of Soil Crumbs: II. Quantitative Studies¹

ABSTRACT

The rate of consumption of sodium periodate by Fargo clay loam surface grassland crumbs was measured at different periodate concentrations, and the degree of subsequent slaking and dispersion of the crumbs in 0.01M NaCl/Na p-nitrophenol was observed. Prior leaching of the crumbs with 0.05M NaCl was essential before crumb stability was reduced appreciably 0.250 mmoles of periodate per gram of soil.

Release of the effective inorganic and organic binding agents by NaCl, Na₄P₂O₇, and NaIO₄ treatments was studied quantitatively. The effect of periodate oxidation alone was demonstrated when no measurable release of organic matter occurred with preliminary leaching by 0.05M NaCl. The amount of periodate consumed by the grassland crumbs was more than could be accounted for by primary oxidation of the carbohydrate present.

The loss in strength for the grassland crumbs, after systematic removal of the binding agents, was measured quantitatively by means of a plummer balance. The effect of prior leaching with 1M NaCl followed by 0.05M NaCl also was investigated. After the combined treatments, dispersion was still incomplete for the Fargo crumbs, indicating some residual bonding. The dispersion of Houston Black clay crumbs was complete, however, when 0.1M Na₄P₂O₇ was substituted for 1M NaCl. The organic material released by either NaCl or Na₄P₂O₇ stabilized the claysized fraction of the soil only. The periodate-oxidizable substances stabilized both the silt- and clay-sized fractions.

¹ Contribution from the Soil and Water Conservation Research Division, ARS, USDA, in cooperation with the Department of Soil Science, University of Minnesota, St. Paul. Paper No. 5184 Scientific Journal Series.

² Research Chemist and Research Soil Scientist, respectively, St. Paul, Minn. W. W. Emerson was on leave during 1961–62 from CSIRO, Division of Soils, Adelaide, South Australia.

Received for publication April 15, 1964. Accepted for publication November 10, 1964.