The quantity–intensity relationships between gains and losses of exchangeable K of the soil, and the K-intensity in the equilibrium solution, were determined for two soils incubated at 25 ± 1 °C for 0, 2, 4, 6 and 8 weeks under submerged conditions. The Kintensity modified to include the factor (F) by which Mg differs from Ca in its behaviour on the exchange complex, i. e. aK/(a½Ca + F.a½Mg), gave significantly lower values of equilibrium activity ratio, , and higher values of linear buffering capacity (LBCK), than when measured by the simple ratio, aK/(aCa + aMg)½. The mean value of the factor, F, was 0·46 for Conlubang sandy loam and 0–49 for Luisiana clay. Submergence up to 2 weeks resulted in an increase in the equilibrium activity ratio, , by 43–3% in Conlubang sandy loam. In Luisiana clay, , increased slightly after an initial decrease. In both soils, the readily exchangeable K, , increased with submergence, more so in Conlubang sandy loam than in Luisiana clay. Linear buffering capacity, LBCk, which is a measure of the rate of release of K to the soil solution, increased markedly with soil submergence.