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Potassium and Magnesium Availability in Mudstone Coal Overburdens in West Virginia¹

ABSTRACT

Mudstones are rapidly weathering sedimentary rocks with a hardness of < 2.5 (gypsum = 2.0, calcite = 3.0) and are dominated by silt-and/ or clay-sized particles. They may contain abundant amounts of Ca, Mg, and K, and may have a high neutralizing potential. Mixing mudstones containing high amounts of K and Mg with infertile top-soils when reclaiming surface mined lands may increase the fertility of the resulting mine soil. The objective of this experiment was to determine which soil testing procedure(s) would best predict the availability of K and Mg to plants from nine mudstone samples associated with seven coal seams in northern West Virginia.

The soil testing procedures used to extract K and Mg from the mudstones were double acid (0.05N HCl and 0.025N H₂SO₄), boiling 1_N HNO₃ (nitric acid), neutral 1N NH₄OAC (ammonium acetate), water, and Baker's small exchange method. The biological extraction of K and Mg by oat seedlings (Avena sativa L.) was determined with a modified Stanford-DeMent procedure.

Except in mudstones where toxic elements are present, such as the Clarksburg samples, it appears that mudstones are a possible source of plant-available K in newly constructed mine soils. The HNO₃, NH₄OAC, and Baker tests predicted the relative availability of K in the mudstones. The HNO₃ test was best able to predict the total amount of K available to the oat seedlings.

Although there was a large amount of HNO₃-extractable Mg in the high-pH mudstones, it was not available to the oat seedlings. If, as postulated, the Mg in these mudstones was in the carbonate form, it may become available over time in the humid regions where the mudstones occur.

Key Words: available nutrients • soil extraction

¹ Contribution of USDA-ARS, Beckley, WV 26805, and Division of Plant and Soil Sciences, West Virginia University. Published with the approval of the Director of the West Virginia Agricultural and Forestry Exp. Stn. as Sci. Paper no. 1678.

² Former Graduate Assistant, now Graduate Assistant at University of Florida, Gainesville, FL 32611; and Research Soil Scientist, now at U.S. Regional Pasture Research Laboratory, University Park, PA 16802.

Received for publication January 9, 1981.