Diffusion of cations in soils

The rate at which nutrients move through soil can possibly limit their availability to plants; in some cases this movement is mainly by diffusion. Several studies of cation diffusion in soils have been reported. For soils or similar materials, the most easily interpreted diffusion measurements relate to self-diffusion which can be studied when a concentration gradient of radiotracers is set up in a system where the non-radioactive ions are uniformly distributed. In this paper a method of determining self-diffusion coefficients for cations is described and previously published results obtained by this method are reconsidered together with some unpublished data. The role of cation diffusion in plant nutrient supply is discussed in the light of these results