A method for dispersing Chilean Ando soils (trumaos) was investigated at the Soil Science Department of the University of Concepción at Chillán, Chile.
The method, originally proposed by Jackson (USA) and Fieldes (New Zealand) consisted of the elimination of monovalent and divalent cations, and the removal of organic matter, free iron and aluminum oxides and allophane. The dispersion was obtained by treating the sample with 2% Na2CO3, pH 10,8.
The method proved to be useful when applied to the Chilean soils derived from reeently deposited volcanie ash.
The results show that flocculation, whieh oecurs with the Bouyoucas ar Pipette methods, is avoided in the proposed method.
It is also shown that the texture of these soils ean not longer be considered as loam, but rather as clay which agrees with the tremendaus reactivity presented by these sails.
The experimental work suggests that free Fe2O3 may be the agent inducing floceulatian in these sails.

1 Ingeniero Agrónomo M. S., Profesor Departamento de Suelos, Facultad de Agronomía, Universidad de Concepción