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 Na(2)CO(3) fusion, HClO(4) digestion, HClO(4) + HNO(3) digestion, HF + HClO(4) digestion or NaOBr oxidation methods. In order to test the suitability of the HF + HClO(4) digestion the results obtained by this method were compared with the others above, especially the Na(2)CO(3) fusion which is accepted as a standard method. The phosphorus amount found with the HF + HClO(4) digestion method were almost the same as the phosphorus amount by the Na(2)CO(3) 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.