Relationship between pore size distributions and physical properties of clay soils

Pore size distributions using mercury injection and nitrogen sorption techniques were determined on a number of soils classified as clays on the basis of particle size analysis. Some of these soils exhibit markedly different consistencies during texturing and undergo changes in texture during prolonged manipulation, e.g. subplastic, superplastic and self-mulching soils. The pore size distributions for these soils do not differ significantly from those obtained for the normal labile clay soil in the pore size range 2 nm to 50 �m. The clay soils examined, with the exception of the krasnozem, have the majority of their pore volume within pores smaller than 10 nm with the predominant pore size centred around 3 nm plate separation. In the case of the krasnozem, the particle size analysis does not correspond to the texture assessment as a clay loam. Surface and subsoil samples of the krasnozem have high porosities and predominant plate separations of 6 nm. They consequently possess significantly different pore size distributions from the other clays. In the case of the surface sample, only a small proportion of its total pore volume is in pores smaller than 10 nm. These differences in pore structure observed between the krasnozem and the other soils examined may result from differences in mineralogy, and in particular from the high sesquioxide content of the krasnozem.