Phosphorus and trace metals in serpentine-affected soils of the Sumas Basin, British Columbia

Soils of the Sumas watershed in the Lower Fraser Valley of British Columbia have contrasting P, Mg and trace elements contents arising from two major sources, periodic deposition of serpentine-rich sediments and intensive agricultural activities. Four study sites were examined for soil P by several extractants commonly used for P availability assessments. The results were compared with aqua regia to determine best estimates of extractable P. In addition, these extractants were evaluated as indices of associated trace metal amounts. Aqua regia, acid ammonium oxalate and 1 M HC1 extracted similar amounts of P and trace metals. Acid ammonium oxalate was found to be closely related to the estimates of total P and recoverable elements, followed by 1 M HC1. There was clear separation of the sites by both P values and trace elements associated with serpentine (Cr and Ni) and those from agricultural activities (Cu and Zn). Results suggest that a single extraction, 1 M HC1, can be an effective measure of both available P and trace elements in serpentinitic soils.