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Managanese Oxide Minerals in Nodules of Two Soils of Texas and Alabama¹

ABSTRACT

Elemental analyses were made to determine the total Mn and other selected metal elements in the nodules and whole soils of Benchley (Vertic Argiustolls) (Texas) and Decatur (Rhodic Paleudults) (Alabama). Also, DTPA-extractable Mn in the whole soils was determined as a measure of Mn available to plants. Managanese oxide minerals in soil nodules were magnetically concentrated, and subsequently identified by x-ray diffraction (XRD), selective chemical treatments and various thermal methods. Tentative identification of one Mn oxide was done by high-resolution transmission electron microscopy. The greatest concentration of Mn was in the surface horizon of Decatur and in the subsoil of Benchley. Most of the Mn was in the coarser soil fractions. Zinc, Li, Ba, Cu, Mn, and Fe were more concentrated in the nodules than in the respective whole soil. The correlation between DTPA-extractable Mn and total Mn was high for Benchley and Decatur whole soils. Two Mn oxide minerals, birnessite and lithiophorite, were identified in the nodules of Benchley. Preferred oriented slide mounts and magnetic concentration of the samples aided in Mn oxide identification by XRD. Lattice fringes attributed to todorokite also were observed in Benchley nodules. Lithiophorite was identified in the nodules of Decatur. Other minerals found in the nodules include smectite, kaolinite, quartz, and goethite in Benchley, and kaolinite, quartz, and hematite in Decatur. Calcium, Zn, Li, Ba, and Cu detected in Benchley and Decatur nodules may be part of the Mn oxide mineral structures.

¹ Contribution from the Texas Agric. Exp. Stn., College Station, TX (Technical Article no. 20775).

² Former Research Associate and Professor of Soil Science, Dep. of Soil and Crop Sciences, Texas A&M Univ. The first author is now Assistant Professor, Dep. of Plant Science and Technology, North Carolina A&T State Univ., Greensboro, NC 27411.

Received for publication July 22, 1985.