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
