Abstract: | Abstract Elevated soil phosphorus (P) content is common in the central coastal valleys of California, the result of decades of the intensive vegetable production. Undesirably high P concentration in surface water in this region stimulated interest in evaluating techniques to rank the potential for soil P loss to the environment. Phosphorus availability of 25 representative soils from fields in vegetable rotations were evaluated by the following techniques: bicarbonate‐extractable P (Pbc)–calcium chloride, extractable P (Pcc), P extractable by iron‐impregnated paper (PFe), P extractable by anion exchange resin (Pae), and the degree of P saturation (Psat). A column study was conducted in which these soils were evaluated for soluble P concentration in runoff and leachate from two simulated irrigation events. There were strong correlations among all measures of soil P availability (r=0.66–0.90). Runoff soluble P was most strongly correlated with Pcc, Pae, and Pbc (r=0.98, 0.93, and 0.91, or 0.98, 0.90, and 0.85 in the first and second irrigation, respectively). The relationship of runoff soluble P to Pbc, Pae, and Pcc was characterized by a change point; runoff soluble P from soils <50 mg kg?1 Pbc was minimal, whereas at higher Pbc runoff P reached levels of environmental concern. Leachate soluble P was also correlated with Pcc, Pae, and Pbc (r=0.84–0.99). Across soils, leachate soluble P averaged 1.4 mg L?1, compared to 0.11 mg L?1 for runoff P. We conclude that Pcc, Pae, and Pbc are useful tests to rank the potential for P loss in irrigation runoff or drainage. Given the relative complexity of the Pae technique, Pbc and Pcc appear to be the most practical soil tests for this purpose. |