| Abstrakt: |
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 (P bc )–calcium chloride, extractable P (P cc ), P extractable by iron‐impregnated paper (P Fe ), P extractable by anion exchange resin (P ae ), and the degree of P saturation (P sat ). 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 P cc , P ae , and P bc (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 P bc , P ae , and P cc was characterized by a change point; runoff soluble P from soils -1 P bc was minimal, whereas at higher P bc runoff P reached levels of environmental concern. Leachate soluble P was also correlated with P cc , P ae , and P bc (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 P cc , P ae , and P bc are useful tests to rank the potential for P loss in irrigation runoff or drainage. Given the relative complexity of the P ae technique, P bc and P cc appear to be the most practical soil tests for this purpose. [ABSTRACT FROM AUTHOR] |
