Clay dispersivity and crusting of soils determined by Buchner funnel extractions

Abstract

Soil dispersivity tests strongly disturb soils and therefore only remotely reproduce conditions in the field. A quick and inexpensive laboratory method for the assessment of clay dispersivity of soils is proposed that involves a much milder soil treatment. The method is based on the observation that, during the separation of the soil solution from soil pastes, the separated soil solution in some soils contains suspended fine matter. The method involves the consecutive extraction of wetted and only mildly disturbed soil packed in a Buchner funnel, under standardized conditions. The time needed for the completion of the extraction of 20 mL of solution, and the extracted mineral load, are monitored. After drying, the micromorphology of the soil cake can be observed by scanning electron microscopy. By this method, the results obtained from six South African soils compared well with spontaneous dispersion test data (after Rengasamy et al., Aust. J. Soil Res., 1984, 22, 413-31) obtained independently.