A basis for soil mesomorphological analysis

SUMMARY To bridge the gap between description of soil in the field, i.e. macromorphology (which is usually qualitative), and micromorphology (which may be quantitative), a technique for mesomorphological description is presented. Undisturbed vertical soil monoliths are impregnated with epoxy resin and features of interest are quantified using image analysis. Resin is applied, in the field, to the soil profile. A monolith is excavated and resin is applied to the reverse side which is then ground flat with a disc grinder. The prepared surface is then presented to a video camera for image capture. In general, the resolution is > 0.2 mm and the field of view is 100 × 500 mm. This scale permits details of horizons to be quantified and the relationship between features of interest in different horizons to be discerned. The technique is illustrated by quantifying the pore structure and distribution of manganese/ iron-rich material (nodules and some rock fragments) in the first three horizons of a Paleustalf. The attributes measured on each of these features are the volume proportion and surface area. The three horizons may be distinguished by the quantity and two-dimensional pattern of the pore structure. The macroporosity (volume proportion of pore space) and surface area are greatest in the surface horizon, smallest in the second horizon and intermediate in the third horizon. The concentration of manganese/iron-rich nodules is at a maximum in the second horizon which corresponds to the region of least macroporosity.

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