The Measurement of Exchangeable Aluminum in Soils and Clays

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Abstract
The 1N salt leaching of Al‐saturated soils and clay samples or of acid subsoil materials with native ion saturations resulted in the displacement of Al+++ions in amounts close to the exchange capacity for the Al‐saturated materials and near capacity minus exchangeable Ca + Mg for the acid subsoils. Prolonged leaching with neutral salt solutions did not displace quantities of Al significantly larger than those which were present on exchange sites. Acidified salt solutions, on the other hand, continued to dissolve Al. One normal solutions of KCl, CaCl2 and NaCl removed the same amounts of Al from a number of soils and clays, so long as the leaching was sufficiently exhaustive. For limited leaching, KCl was the most effective displacing agent and NaCl the least.Potentiometric titrations of some Al‐saturated or naturally acid soils and clays to pH6 in 1N KCl consumed quantities of base equivalent to the Al displaced by salt‐leaching or determined by conductimetric titration. With other soils, containing mostly kaolin minerals and iron oxides, the acidity which could be titrated was significantly larger than the amount of Al which could be displaced.

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