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Cation-Exchange Capacity and Exchangeable Cations in Piedmont Soils of North Carolina¹

ABSTRACT

Soils of the North Carolina Piedmont were analyzed for permanent- and pH-dependent charge components of cation-exchange capacity. Permanent charge was taken as the summation of exchangeable metal cations, including Al displaced upon leaching with a neutral salt solution; pH dependent charge was regarded as the amount of exchange acidity (BaCl₂-TEA) remaining after neutral salt leaching.

Well-developed upland soils had small permanent charges and large pH dependent charges. For soils of a given sequence, the permanent-charge/pH-dependent charge ratios (B₂ and above) were smallest for the red end member. Deeper horizons often had very large permanent charges, as did the B horizons of some Planosols. Latosolic soils had smaller permanent-charge/pH-dependent charge ratios than did Red-Yellow Podzolics.

Permanent-charge components of CEC were countered exclusively by metal cations. In acid soils Al predominated, while Ca and Mg neutralized most of the permanent charge in soils with pH's above 6. There were negligible amounts of electrostatically-bonded H in any soil. Generally exchangeable Al increased with depth. Yellow Podzolic and Planosolic soils in particular tended to have large amounts of exchangeable Al in lower horizons.

Percentage base saturation concepts are discussed, the conclusion being that a saturation percentage based on permanent charge is preferred.

¹ Published with the approval of the Director of the North Carolina Agr. Exp. Sta. as Paper No. 907 in the Journal Series. Presented before Div. V, Soil Science Society of America, Nov. 21, 1957, at Atlanta, Ga.

² Professor of Soils, Assistant Professor of Soils, and Associate Professor of Soils, respectively.

Received for publication July 7, 1958. Accepted for publication August 1, 1958.