Evaluation of Soil Tests as a Measure of Phosphorus and Potassium Availability in Illinois Coal Waste

Abstract

Abstract The Mitscherlich‐Bray relationship was applied to soil test‐extractable P and K in coal waste, and yield of tall fescue ( Festuca arundinacea Schreb.) grown in the waste at pH 6.5. The typical exponential function between yield and extractable P obtained with soil‐grown plants was not exhibited by the waste‐grown plants for dilute acid or acid ammonium fluoride extractants, partly because values > 15 mg/kg extractable P in the waste could not be obtained despite heavy P fertilization. Correlation coefficients ( r 2 ) for extractable P in the growth media vs. P concentrations in shoots were 0.45 for the waste, and 0.81 for Elliott silt loam. Results with extractable K and yield on the waste were inconclusive, due to the confounding effect of an apparent Ca interference with K uptake. It is concluded that results of “soil testing” for P and K in coal waste should be interpreted with caution; in some cases, the tests may be inappropriate as indices of available forms of these elements in the waste.