Secondary Carbonates in Three Fine and

Fine-loamy Alfisols in Michigan

Randall J. Schaetzl, William E. Frederick, and Lawrence Tornes

Secondary pedogenic carbonates are usually associated with ustic or drier soil moisture regimes; when found elsewhere, their interpretation can be troublesome. We studied three Alfisol pedons in Michigan that contained secondary carbonates on ped faces. The purpose of the research was to (i) characterize these accumulations, (ii) examine possible genetic explanations for the accumulations, (iii) determine if these soils have calcic horizons, given the recent redefinition of this diagnostic horizon, and (iv) evaluate how current k horizon nomenclature might apply to these soils. Three different drainage classes and two soil temperature regimes were represented in the sampled pedons: a fine, mixed Glossic Eutroboralf; a fine, illitic, mesic Aquic Hapludalf; and a fine-loamy, mixed, mesic Aeric Endoaqualf. All three pedons had thin (<50 cm) leached zones near the surface, and carbonate coatings (calcans) on ped faces within the lower B and/or upper C horizons. Two of the three pedons had horizons that met calcic horizon criteria. Horizons of preferential carbonate accumulation sometimes occurred near subtle textural breaks in the lower solum. Some B horizons in one pedon contained carbonate accumulations in amounts that exceeded that of the presumed parent material. The calcans have probably resulted both from vertical translocation of carbonates, followed by precipitation at depth, as well as internal redistribution of carbonates from ped interiors to ped faces. Use of the k subscript is warranted for some horizons in these soils. We recommend that its usage should be similar to t or s, i.e., horizons with evidence of secondary carbonates merit the k subscript.