Spodosol-Alfisol Intergrades:  Bisequal Soils in NE Michigan, USA


Randall J. Schaetzl


           Twenty three well-drained Boralfs, most of which exhibit bisequal soil morphology, were described and sampled in NE lower Michigan, where they occur on landscapes shaped by Greatlakean ice ca 12 ka.  Bisequal soils in Michigan are intergrades between Orthods and Udalfs, with a spodic-like upper sequum (A-E-Bs) overlying a sequence of E’-Bt-C horizons.  Thus, they frequently occupy a pedogenic “ecotone”.  The purpose of the study was to characterize these soils, which have been little-studied, and to determine if parent material homogeneity and texture are correlated with various aspects of their morphology.

           The soils have formed in coarse-loamy and fine-loamy materials, often with a distinct lithologic discontinuity between the two sequa.  The lower material, interpreted as glacial till, is strongly calcareous and slightly coarser-textured, with considerably more dolomitic gravel than the upper material.  Water flowing through the material above may “hang” at the discontinuity and deposit illuvial clay; Bt horizons are found at or immediately below the discontinuity.  Statistical correlations indicate that bisequal sola and their eluvial horizons are thicker when developed in coarser-textured materials.  Finer-textured pedons contain more extractable Fe and Al in the spodic sequum, but have thinner eluvial zones which have not been as completely stripped of metal cations.  In the fines-textured pedons, the E’ horizon may be completely lacking.