A laboratory experiment was carried out to see the distribution of sorbed potassium (K) in Old Brahmaputra Floodplain and Madhupur Terrace soils and its subsequent release behaviour for getting an idea on K fertility of these two soils. For sorption, four different concentrations 0, 10, 20 and 30 mg K L-1 were added and kept for 15 days. After the allocated time, one sample of the treated soils was repeatedly extracted with 1N NH40Ac solution to see the K release capacity and another sample was sequentially extracted with distilled water, 1N NH40Ac and H2SO4 for water soluble, exchangeable and non-exchangeable forms of K. The sorption of K increased progressively with increasing K concentrations of the solution. The flood plain soil sorbed higher amount of K compared to terrace soil. The terrace soils from Madhupur farm sorbed K mostly in exchangeable form whereas the flood plain soil from BAU farm sorbed mostly in non-exchangeable form. About 33-41% and 36-62% of added K were released by the first extraction for BAU farm and Madhupur soils respectively, but in following extractions the release of K from BAU farm soil was almost equal or higher than Madhupur soil. The Elovich equation showed a higher rate of K release from Madhupur soil than from BAU farm soil.