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Separation and Functional Group Analysis of Soil Organic Matter¹

ABSTRACT

An investigation was conducted on the Romney silty clay loam and Zanesville silt loam soils to determine an efficient method of separating organic matter from the mineral fraction of the soil with a minimum amount of alteration, and to compare the two soils on the basis of the functional group composition of their organic matter. Soil organic matter was obtained as an organic residue after the sand and silt fractions had been removed from an alkaline soil-water suspension by sedimentation following dispersion of the soil by ultrasonic vibration, and the remaining suspended clay fraction dissolved by repeated treatments with an HCl-HF acid mixture. No loss of organic matter was incurred by the physical removal of the sand and silt fractions, but approximately 12% of the Romney organic matter and 37% of the Zanesville organic matter was dissolved by the acid treatments.

Various chemical and instrumental techniques were used to quantitatively analyze this organic matter preparation for the carboxyl, aliphatic hydroxyl, phenolic hydroxyl, and carbonyl functional groups. The Romney organic matter was characterized by its high carboxyl and carbonyl content, whereas the Zanesville organic matter exhibited a high aliphate hydroxyl content. This comparison of functional group composition indicates a greater state of humification (oxidation) for the Romney organic matter than for the Zanesville organic matter. This difference in functional group composition is a major factor affecting the chemical interactions each type of organic matter undergoes in the soil.

¹ Journal paper no. 3373. Purdue University Agr. Exp. Sta., Lafayette, Ind. Contribution from the Department of Agronomy. This investigation was supported by a grant from the Department of Interior, Office of Water Resources Research. Presented before Div. S-3, Soil Science Society of America, November 1967, at Washington, D.C.

² Graduate Research Assistant, Purdue University, and former Assistant Professor of Agronomy, Purdue University. Present address: Makerere University College, P.O. Box 7062, Kampala, Uganda.

Received for publication June 13, 1968. Accepted for publication October 3, 1968.