Differentiation of an Eluvial Fragipan from Dense Glacial Till in Northern Minnesota
- M. B. Miller,
- T. H. Cooper and
- R. H. Rust
Over the past two decades there has been considerable discussion among soil scientists in glaciated regions of North America regarding the differentiation of a fragipan horizon from dense glacial till. This study was conducted to determine if the Nashwauk soil series (fineloamy, mixed Typic Glossoboralf) has a horizon that meets the criteria for a fragipan. Standard soil survey methods were used for sampling and measurement of physical and chemical soil properties. Micromorphology was investigated using thin sections and the scanning electron microscope. Results from this study indicate that the fragipan is of pedogenic origin. Presently, soil taxonomy does not allow for recognition of the fragipan in the Nashwauk soil series since it occurs above the argillic horizon. The eluvial fragipan (Ex) has many morphological, physical, and chemical characteristics that are significantly different from the underlying, comparatively unaltered, dense loamy glacial till in the lower horizons. There was not sufficient morlogic or particle size evidence, however, to indicate a lithologic discontinuity. Micromorphological observations reveal that close packing of soil particles within the Ex horizon are the likely cause of high soil bulk density, root restriction, and very slow permeability. Citrate-bicarbonate-dithionite (CBD)-extractable silica was lowest in the Bw and Ex horizons. It appears that physical processes rather than chemical processes are primarily responsible for the properties of the fragipan in this soil. Horizons above the Ex are especially susceptible to compaction when wet.
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