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Cation-Exchange Capacity of Plant Lignins and Soil Humic Colloids as Affected by pH and Hydrolysis Error¹

ABSTRACT

The effect of the pH of the buffered saturating solution on the cation-exchange capacity (CEC) of several plant lignins and soil humic colloids isolated by NaOH and 1,4-dioxane was determined for the pH range 2.5 to 8.0. The CEC of lignins ranged from 0 to 38 meq/100 g at pH 2.5 and 33 to 130 meq/100 g at pH 8.0, whereas the CEC of soil humic colloids ranged from 40 to 117 meq/100 g at pH 2.5 and 163 to 367 meq/100 g at pH 8.0. For the same plant or soil material, NaOH-extracted samples were invariably higher in CEC than were dioxane-extracted samples. The CEC values of the root lignins were lower than those of the shoot lignins irrespective of extraction method. The extent of hydrolysis error throughout the pH range was measured using two comparable CEC methods in which a water-wash step was included in one case and omitted in the other. Maximum percentage hydrolysis error occurred at pH 2.5. Dioxane lignins of prairie grass and dioxane extracts of the 0- to 12-inch layer of the virgin and cultivated Prairie soils were found to be more susceptible to hydrolysis errors than their NaOH-extracted analogs.

¹ Contribution from the Department of Soils, University of Wisconsin, Madison. Published with the approval of the Director, Wis. Agr. Exp. Sta. Supported in part by grants under Title IV of the National Defense Education Act of 1958 and Federal Regional Project NC-55. Presented before Div. S-3, Soil Science Society of America, Nov. 18, 1964, at Kansas City, Mo.

² Research Fellow, Associate Professor, Research Assistant, respectively.

Received for publication March 3, 1965. Accepted for publication July 7, 1965.