Relationship between flame photometry and ICP-MS detected potassium concentrations extracted in calcium chloride for paddy soils samples

Ammonium acetate extracted and Flame photometry (FP) detected potassium (K) concentration is widely used to determine the exchangeable K in paddy soils. Recently, inductively coupled plasma mass spectrometry (ICP-MS) is also used widely in analytical purposes as it has capabilities of simultaneous determination of major and trace elements. Moreover, calcium chloride (CC) is used as a universal extractant when determining mineral elements in soil samples. However, the relationship between FP and ICP-MS detected K concentrations in CC extracted paddy soil samples of Sri Lanka is not known. Therefore, a total of 250 soil samples were collected from lowland rice paddy fields in Sri Lanka representing all three climatic zones (wet, dry and intermediate). Potassium in 4 g of soil was extracted into 40 mL of 0.01 M CaCl2 for two hours in an orbital shaker at the ambient temperature and K concentration was determined by FP and ICP-MS methods. The range of K determined by both methods was similar. The concentration of K ranged from 17.84 mg kg−1 to 490 mg kg−1 in the FP method while it was in the range from 0.00 mg kg−1 to 492 mg kg−1 in the ICP-MS method. The mean K concentration detected by the FP method was greater (136±5.98 mgkg-1 ) than that by the ICP-MS method (64.0±3.95 mgkg-1 ), indicating lower sensitivity of the ICP-MS method than FP. The relationship between the FP and ICP-MS detected K was K(FP) =0.52 × K(ICP-MS) − 6.64 with a R 2 value of 0.61 (p<0.000). Therefore, ICP-MS and FP detected K concentrations are interchangeable when determining K concentration in paddy soils extracted using the CC method. Due to the use of soils from a wide range of soils and concentrations, derived relationships are robust.