A Rapid Method to Determine Total Phosphorus in Soils

Abstract Present methods for extracting total phosphorus (P) from soil samples are tedious and time consuming. A rapid and precise extraction procedure was developed in which sequential additions of concentrated H 2 SO 3 , H 2 O 2 , and HF were made to soil samples. This was followed by 10 min of heating (≃ 423 K) to eliminate excess peroxide. The entire procedure required about 30 min. The proposed method was compared to standard Na 2 CO 3 ‐fusion and HClO 4 ‐extraction methods. Almost equal amounts of P were extracted by the proposed and Na 2 CO 3 ‐fusion methods. About 7% less P was found in HClO 4 extracts. In the proposed method, treatment with H 2 O 2 was used to oxidize P associated with the organic carbon. Treatment with HF was necessary to solubilize P associated with the aluminosilicate minerals found in sandy soils that are low in organic C. The proposed method is not only more rapid than those previously used, but is easily performed at minimal cost with simple laboratory equipment. It is especially useful for analyzing small numbers of soil samples, and should be useful to evaluate P dynamics in sediment transport (erosion) studies, and in soil formation and degradation studies.