DISTRIBUTION OF AVAILABLE MANGANESE IN KENTUCKY SOILS1

Abstract

Laboratory studies were conducted to determine fractions of native soil and applied 54Mn that contribute to the Mn extracted by DTPA (0.005 M diethylenetriamine pentaacetic acid, 0.005 M CaCl2, 0.1 M triethanolamine, pH 7.3). Since DTPA-extractable Mn is closely related to Mn uptake by plants, such studies should provide information about fractions of soil Mn that contribute most to its being taken up by plants. Soil types (8), varying in pH from 4.8-7.0, were treated with 448 kg N/ha as NH4NO3 and labeled with 1 .mu.Ci 54Mn (as 54MnCl2)/100 g of oven-dry soil. Samples of each soil were fractionated in sequence into water-soluble, exchangeable, organically bound, reducible, Fe-bound and residual Mn fractions before and after extraction with DTPA. The reducible fraction accounted for an average of nearly 45% of the total Mn before DTPA extraction. The exchangeable, organic and Fe-bound fractions each contained intermediate amounts (13-19%), and the water soluble had less than 2% of the total. The distribution varied widely among soils and generally was related to initial soil pH. With some exceptions, soils of lowest pH had the highest amounts of water-soluble, exchangeable and organic Mn, whereas soils of highest pH contained large amounts of reducible Mn. The distribution of added 54Mn in soil, both before and after DTPA extraction, generally paralleled that for native soil Mn. The extraction of native Mn or added 54Mn by DTPA varied among soils and generally was related to soil pH. In soils of lowest pH, the exchangeable, organic and reducible fractions contributed most to the Mn extracted by DTPA. In soils of highest pH, the reducible fraction contributed most to extractable Mn.