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Evaluation of Soil Tests as a Measure of Phosphorus and Potassium Availability in Illinois Coal Waste¹

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 (r²) 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.

Key Words: calcium and potassium interaction • fixation of fertilizer phosphorus • Mitscherlich-Bray equation • phosphorus and potassium uptake

¹ Contribution of the Dep. of Civil Engineering, Northwestern University.

² Associate Professor and Graduate Research Assistant, respectively, Northwestern University.

Received for publication October 18, 1982.