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Chemical Extraction and Crop Removal of Manganese from Air-Dried and Moist Soils¹

ABSTRACT

Oats were grown in the greenhouse on 20 different soils which had been stored in a moist condition prior to potting. Available soil Mn was estimated by extraction with 1.5M NH₄H₂PO₄, 1.0N H₃PO₄, and 0.1N H₃PO₄ on moist as well as air-dried soil samples. Correlations with soil and plant Mn showed that extraction of soil Mn from the moist samples with 0.1N H₃PO₄ gave the highest correlation coefficient (0.848). Other extractants resulted in much lower correlation coefficients (0.311 to 0.694), regardless of the sample moisture condition.

In a second greenhouse experiment, oats were grown on seven soils which had been stored under air-dry as well as moist conditions. With one exception, the amount of Mn removed by the oats grown on the previously air-dried soils was equal to or greater than the Mn removed from soils previously stored in a field moist condition.

Chemical extraction of soil Mn from moist as well as air-dried soils revealed that the release of Mn upon drying requires aerobic conditions and is not a simple dehydration phenomenon. Extractions of moist as well as air-dried samples with 0.1N H₃PO₄, 0.05M NaEDTA of pH 9.5, and 0.2% hydroquinone were performed to estimate the weakly acid-soluble, organic, and easily reducible oxides of soil Mn, respectively. The results indicated that the release of Mn upon air drying stemmed from the organic fraction of soil Mn. This release of organically complexed Mn is thought to be a result of chemical oxidation of soil organic matter.

¹ Contribution from the Department of Soils, University of Wisconsin, Madison. Published with the permission of the Director, Wisconsin Agr. Exp. Sta. Presented before Div. IV, Soil Science Society of America, Nov. 18, 1959, at Cincinnati, Ohio.

² Former Research Assistant in Soils, now Assistant Professor of Soils, respectively, University of Wisconsin, Madison.

Received for publication December 3, 1959. Accepted for publication June 14, 1960.