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Influence of Sorbed Hydroxyl and Sulfate on Neutralization of Soil Acidity¹

ABSTRACT

Soils of varying clay mineral characteristics were treated with anion-exchange resin to obtain systems containing either sorbed OH^- or SO₄^2-. They were then equilibrated with Ca(OH)₂, and the neutralization of acidity consisting of permanent charge (Hp), variable charge (Hv) and anion-exchange (Han, principally SO₄^2- absorbed) evaluated. The order of neutralization was Hp (consisting principally of Al³⁺ except in the case of the muck) first, followed virtually simultaneously by Hv and Han. Sorbed SO₄^2- resulted in more strongly acidic systems. Hv is postulated to arise from covalently-bonded H of aquo groups in the coordination sphere of hydrated Al (or possibly Fe³⁺ atoms). The source of Han is postulated to be acid radicals substituted for OH groups, likewise in the coordination sphere of Al and Fe³⁺ associated with clay surfaces or in hydrous oxide crystals. The magnitude of Han, the soil acidity due to sorbed acid radical anions, may be an appreciable part of the total acidity of Red-Yellow Podzolic and Reddish-Brown Lateritic soils.

¹ Published with the approval of the Director of the North Carolina Agr. Exp. Sta. as Paper No. 1693 in the Journal Series. Received Sept. 3, 1963. Approved Mar. 11, 1964. Presented before Div. II, Soil Sci. Soc. Am., Nov. 28, 1961, St. Louis, Missouri.

² Formerly Associate Professor, Soil Science Dept., N. C. State of the Univ. of North Carolina at Raleigh; now Soil Research Advisor, Scott Agr. Laboratories, Nairobi, Kenya.