Prediction of phosphorus availability from 88 Ontario soils using five phosphorus soil tests

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Abstract
Five chemical soil‐P extractants were compared. Surface samples from 88 Ontario soils were collected and used to grow corn (Zea mays L.) in a greenhouse. Soil pH ranged from 5.0 to 7.6 and organic matter from 60 to 575 g kg‐1. The amount of P extracted by the five extractants was used to predict P availability to corn plants. The amounts of P extracted by the five extractants were highly correlated (r = 0.83 to 0.97). The correlation of extractable P to plant P uptake resulted in r2 values of 0.74, 0.73, 0.54, 0.65, and 0.66 for the NaHC03, AB‐DTPA, Bray‐Kurtz P1, Bray‐Kurtz P2, and Mehlich 3 extractants respectively. Adding soil pH to the equations improved the prediction of plant P uptake resulting in R2 values of 0.80, 0.80, 0.70, 0.73, and 0.75 for the NaHC03, AB‐DTPA, Bray‐Kurtz P1, Bray‐Kurtz P2 and Mehlich 3 extractants, respectively. The two alkaline extractants appeared to be equally effective and superior to the three acidic extractants with the Bray‐Kurtz P1 extractant being least effective.