| Abstract: | Abstract Four selected soil tests (Olson's bicarbonate, Bray P‐l, Bray P‐2, and a modified Bray P‐l test) were compared over a four year period as methods for predicting plant available‐P in a slightly alkaline (pH 7.25) minespoil from a west‐central coal field in Illinois. Phosphorus recovery by hybrid corn, measured under both greenhouse and field conditions, showed that the minespoil was extremely P deficient. Extractable Olson's bicarbonate P and standard Bray P‐l phosphorus were highly correlated with total‐P recovery by corn, with respective coefficients of r =0.973 and r =0.957 in the greenhouse; and r =0.998 and r =0.983 respectively, under field conditions. Consistent Mitscherlich‐Bray proportionality constants were calculated from corn grain yields under field conditions in three of four years, after adjustments for annual differences in plant population density. Minespoil was found to require about twice as much extractable‐P (about 40 mg/kg Olson‐bicarbonate or Bray P‐l) as topsoil to support maxiumum corn productivity. It was estimated that more than 500 kg/ha fertilizer‐P will be required to achieve maximum corn grain production in spoil. |
