A soil fractionation related to soil structural behaviour

Abstract

To date, in order to characterise and understand soil behaviour, most emphasis has been placed on surrogate measurements of soil structure. However, a direct assessment of the structure of well-aggregated (pedal) soil samples can provide relevant information on soil organisation and lead to a better understanding of soil behaviour. In this paper, we suggest an original fractionation allowing natural soil structural elements, defined on morphological criteria and related to soil behaviour, to be separated. The soil samples come from 2 tropical sequences widespread in the intertropical zone: a ferrallitic and ferruginous soil sequence from Basse-Casamance (Senegal); and an alluvial soil sequence from the middle valley of the Senegal River. The principle of the fractionation is based on the concept of soil friability, and on the use of an organic solvent to separate primary structural units of soil samples first equilibrated at a specific soil water potential. This optimal soil water potential is selected on the basis of experimental studies and its relevance is discussed in relation to the particular structural properties of the soil occurring at this wetness.