The Effect of Periodate Oxidation on the Strength of Soil Crumbs: I. Qualitative Studies1
- C. E. Clapp and
- W. W. Emerson2
Various methods of extraction and oxidation of soil organic matter were used in combination with a sodium saturation technique to assess the binding strength of wet soil crumbs. The procedure consisted of equilibrating a few 3- to 5-mm crumbs with 0.05m NaCl, treating the crumbs with chemical reagents to remove the effective stabilizing components, and then observing the degree of slaking and dispersion of the crumbs when the sodium ion concentration is reduced. For crumbs from predominantly montmorillonitic or illitic soils, the dispersion solution was either 0.01m NaCl buffered with p-nitrophenol at pH 7 or 0.025m Na2B4O7 at pH 10. For kaolinitic soils a more severe dispersion technique was required.
The stability of crumbs formed under long-term grass was reduced greatly by oxidation of the organic matter with 0.05m NaIO4 followed by extraction with Na2B4O7. Complete dispersion in Na2B4O7 or NaCl/Na p-nitrophenol was obtained when a preliminary extraction with neutral Na4P2O7 was followed by periodate oxidation. The stability of corresponding cultivated crumbs was destroyed completely without pyrophosphate extraction in a shorter period of oxidation. Surface crumbs from wooded sites on the same soils showed extreme resistance to all treatment combinations. It appears that there are two types of polymeric organic material binding the grassland crumbs together, one extractable by pyrophosphate and the other oxidizable by periodate.
Samples from Houston Black clay behaved anomalously until the CaCO3 was removed by dilute HCl treatment in the cold. The latter process in itself caused no loss in strength of the crumbs.
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