Effect of the method of dispersion on the yield of clay and fine clay

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Abstract
Because the relative proportion of fine (< 0.2 µm) and coarse clay (2-0.2 µm) is considered an important pedogenetic and taxonomic criterion, the effect on yield of these fractions by different methods of dispersion was investigated for a sandy loam and a clay from the Urrbrae loam. Both soils showed a continued increase in fine clay with time of shaking even after 14 h. This may be a subplasticity effect or due to attrition of coarse clay. Electron micrographs showed that incrustations on coarse clay particles may be a source of fine clay. The amount of total clay from the sandy loam soil continued to rise after 14 h of shaking, but yield from the clay soil was constant after 100 s. Of the chemical treatments only sodium hydroxide had a significant effect. This treatment lead to a marked decrease in the proportion of fine clay. The amount of total and fine clay was unaffected by the 1iquid:solid ratio in the dispersing medium.