Investigation of suitable digestion methods for the determination of total phosphorus in soils

Total phosphorus in five soils with different compositions which were obtained from different places were extracted by using Na2CO3 fusion, HClO4 digestion, HClO4 + HNO3 digestion, HF + HClO4 digestion or NaOBr oxidation methods. In order to test the suitability of the HF HClO4 digestion the results obtained by this method were compared with the others above, especially the Na2CO3 fusion which is accepted as a standard method. The phosphorus amount found with the HF + HClO4 digestion method were almost the same as the phosphorus amount by the Na2CO3 fusion method, while the superiority in extracting phosphorus when compared to other methods were obvious. The methods used in the study were evaluated according to the recovery of total phosphorus, ease of application and rapidity with which they were performed. Orthophosphate in the soil extracts was determined by the molybdenum blue colour method. The relationships between methods are examined statistically. (C) 1997 Elsevier Science B.V.