Comparison of extraction and detection methods of exchangeable Potassium in paddy soils in Sri Lanka

Abstract

Extracting potassium (K) with ammonium acetate (AA) and detecting under flame photometer (FP) is widely used to determine the exchangeable K concentration. Moreover, calcium chloride (CC) is used as a universal extractant (simultaneous extraction of many elements) and the concentration of these elements are detected using inductively coupled plasma emission mass spectrometry (ICP-MS). Therefore, this study aimed to examine the relationship between 1 M AA extracted K detected using the FP method and 0.01 M CC extracted K detected using the ICP-MS method. A total of 250 soil samples were collected from lowland paddy fields in Sri Lanka representing three climatic zones and 19 districts. Extraction and detection protocols of K were as mentioned above. Results revealed that the mean exchangeable K detected by ammonium acetate-flame photometer (AA-FP) method was greater (250±9.2 mg kg−1) than the calcium chloride- ICP-MS (CC-ICP-MS) method (64±3.4 mg kg−1). Concentration of K determined by AA FP method ranged from 34 mg kg−1 to 803 mg kg−1 while that by the CC-ICP-MS method ranged from 0 mg kg−1 to 373 mg kg−1. The relationship between the exchangeable K by the AA-FP method and CC-ICP-MS method was K (CC-ICP-MS) = 0.288 × K (AA-FP) −7.25 with a R2 value of 0.58 (P<0.001). Therefore, CC-ICP-MS can be used as a reliable and convenient method to determine the exchangeable K in paddy soil in Sri Lanka