Cation-exchange capacity at field pH and its relation to the affinity of soils for individual cations

Abstract

A good measure of cation-exchange capacity at field pH was obtained by equilibrium leaching with 0.025M CaCb and estimating the quantity of Ca retained in the soil by a weighing procedure, but not by washing with ethanol. Except on soils with very high levels of exchangeable aluminium, equilibrium leaching with a solution containing 2.0, 0.5, 0.4, and O.4mM of CaS04, MgS04, KCl, and KH2P04 respectively gave values of total adsorbed cations very similar to cation-exchange capacity obtained with 0.025M CaCI2. The multiple cation solution can be used to rank soils according to their affinity for individual cations. Effective relative affinities and effective cation-exchange capacity therefore can be assessed with the same solution.It was found that the selectivity of soils for cations, and therefore the ratio of affinities for a pair of cations, greatly varies with pH.

Sources of potassium taken up by ryegrass from some soils of the North Island

“…Exchangeable potassium (Kx) was determined by leaching with molar ammonium acetate at pH 7. Cation exchange capacity (CEC) and K retention (EAk) were determined by equilibration with an unbuffered standard solution containing Ca 2+, Mg2+, and K+ (During 1973). Soil pH was measured in a water: soil slurry at a ratio of 2.5: 1.…”