The release of nonexchangeable potassium from certain soils of northern Greece

The release of nonexchangeable potassium from the surface layers of nine red soils, sampled in different districts of northern Greece, was studied by treatment of the samples with H⁺-resin at various soil: resin ratios and temperatures and in a pot-experiment with rye grass. It was thus found that, the phenomenon of K-release from the soil samples during their treatment with the H⁺-resin, follows typically the kinetics of the first order opposing reactions under all conditions tested. A close relationship was shown to exist between nonexchangeable potassium released by cropping (defined as K-supplying capacity of the soil) and that released by treatment with the resin. The K-supplying capacity of the soils studied seems to be more closely related to the total amount of lattice-K released by the resin than to the rate of the release. The latter is affected considerably not only by temperature changes but also by changes in the soil:resin ratio. A value for the activation energy of the release reaction was calculated which might be considered as lending additional support to the view, already widely accepted, that K-release in the soil is a diffusion-dependent phenomenon.