An Alkaline Oxidation Method for Determination of Total Phosphorus in Soils

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Abstract
A simple and precise method for determination of total phosphorus in soils and lake sediments is described. A mixture of soil and sodium hypobromite solution is boiled to dryness in a sand bath (260–280°C), and the total amount of orthophosphate is extracted with 1N H2SO4 and determined colorimetrically by the molybdenum blue method. Analysis of a group of diverse soil, lake sediment, and sewage sludge samples indicated that the proposed method and the HClO4 digestion method give essentially the same total P values. With 10 soils, the average results by the proposed NaOBr oxidation method were 1% higher than those obtained by the HC1O4 digestion method and 4% lower than those obtained by the Na2CO3 fusion method. A comparison of methods used for colorimetric determination of the orthophosphate extracted indicated that the results by the recently developed method by Dick and Tabatabai agree closely with those obtained by the method of Murphy and Riley. Digestion of samples with sodium hypobromite solution and colorimetric determination of the extracted P by the method of Murphy and Riley permits rapid analysis of a large number of samples at one time.

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