Physical and clay mineralogical properties of some Natal and eastern Transvaal soils

Abstract

Soils, collected from the south-eastern Transvaal, Natal north coast and the more arid areas of the Natal interior, were examined using physical, chemical and mineralogical methods. Most of the soils were associated with particular management problems such as poor internal drainage, high bulk density or clay dispersion. The results of the investigation confirm that there is a relationship between clay mineralogical composition and physical behaviour. Poorly drained soils tended to be dominated by smectite minerals, while dispersive and compact soils had a mixed clay mineralogical composition of smectite, mica and kaolinite. Problem-free soils were generally kaolinitic. The presence of iron oxides, as indicated by colour, had an ameliorative effect on the physical properties, tending to reduce swelling, dispersion and compaction. Properties such as modulus of rupture, coefficient of linear extensibility and Atterberg limits, successfully discriminated between soils associated with different management problems.