Determination of Total Phosphorus in Soils: A Rapid Perchloric Acid Digestion Procedure

Abstract Extraction and colorimetric methods were evaluated for determining total P in soils. A procedure involving simultaneous digestion of 60 soil samples with perchloric acid and determination of extracted orthophosphate with an ascorbic acid method was evaluated. Analysis of diverse soils indicated that the proposed and conventional HClO 4 digestion procedures yielded essentially the same total P values; however, both HClO 4 methods underestimated total P by 1–6% when compared to Na 2 CO 3 fusion. A comparison of colorimetric orthophosphate procedures indicated the method of Murphy and Riley (1962) was suitable for determination of orthophosphate following either HClO 4 digestion or Na 2 CO 3 fusion. Determination of total P in soils by tube HClO 4 digestion and estimation of extracted P by the method of Murphy and Riley (1962) enables rapid and precise estimation of total P in a wide range of soils.