Fig. 5. Gapon selectivity coefficient (K_G) (upper panels) and natural logarithm of the Vanselow selectivity coefficient (ln Kv) (lower panels) as a function of the equivalent adsorbed fraction of K (E_K). Data are for the <2-mm fraction (filled circle) of the nontreated soil, and for the 2Bt3 clay fraction (triangle) that was treated with H₂O₂ to remove organic matter and citrate-dithionite to remove free Fe oxides before dispersion and particle-size fractionation