Abstract: A laboratory experiment was carried out on ion [viz. NH4+, C, Ca2+, P (HPO42– + H2PO4–), SO42– and NO3–] sorption behaviour of Old Brahmaputra Floodplain soil with a view to examine the amount of ion sorbed by soil when recommended doses of N, P, K and S fertilizers are applied at different moisture regimes i.e. 5 cm standing water (low concentration), saturated condition (medium concentration) and field capacity (high concentration). Results showed that there was a wide variation in ion sorption for different moisture regimes as well as times. In general, the sorption of different cations and anions increased with the increase in ionic concentration i.e. ionic strengths of the solution and the maximum sorption was found at saturated condition (medium concentration). The sorption of Ca2+ was the highest followed by NH4+ and K+. Among the anions the P sorption was the highest followed by NO‾ and SO4–2.