Strong Acid Extraction Methods for “Total Phosphorus” in Soils: EPA Method 3050B and EPA Method 3051

Core Ideas: Many agricultural labs have added environmental tests to their repertoire of protocols. These labs test various media (soils, waste residuals, manures, and runoff waters) for P. Almost no rigorous comparisons indicate what methods are best suited for this purpose. We compared EPA 3050B and 3051 (with/without HCl) on various acidic and alkaline soils. Both EPA 3050B and EPA 3051 gave reliable and comparable results. The emphasis on controlling environmental phosphorus (P) losses from agriculture has expanded the role of agricultural laboratories in testing a variety of media for P, including soils, waste residuals, manures, and runoff waters. To estimate total P in soils, strong acid extraction methods, which actually measure total recoverable P, are generally used because true total digestion methods (e.g., USEPA method 3052 or perchloric acid digestion) possess an array of operational concerns and safety limitations and also typically extract forms of P that are of limited environmental import. We sought to assess the merits of two strong acid extraction methods, USEPA method 3050B and USEPA method 3051 (both with and without hydrochloric acid [HCl] addition), on a variety of acidic and alkaline soils typical of the northeastern United States. Both methods gave reliable results, although method 3050B without HCl showed somewhat lower (though not statistically significant) extraction efficiencies. Method 3051 was unaffected by the addition of HCl, and its extraction efficiencies were approximately 7% greater when compared to method 3050B, although the differences were only significant in one of the seven soils tested.