Fundamental Changes in Soil Taxonomy: The Mollic Epipedon.

Soil Taxonomy was developed in the 1950’s by a number of individuals and groups called “Soil Survey Staff.” Seven preliminary drafts were circulated in the 1960’s. The first and second completed editions of Soil Taxonomy were published in 1975 and 1999, respectively. A series of 12 updates to the keys and differentiae have been published from 1975 – 2014 as editions of Keys to Soil Taxonomy. Because of the increased complexity of Soil Taxonomy and the difficulty in teaching soil classification to students using Keys to Soil Taxonomy, version 2.0 of a web-based Illustrated Guide to Soil Taxonomy (IGST) was published in 2015 that contains simplified classification keys to the great group level in addition to many illustrations, photos, and hyperlinks. Our objectives are to (1) propose simplifying the classification keys for the mollic epipedon and (2) discuss how these simplified classification keys for the mollic epipedon can be used as a model in future fundamental revisions of Soil Taxonomy. For the mollic epipedon, we propose a concise thickness requirement and a simplified list of required criteria throughout the thickness requirement including color, organic carbon content, base saturation, and soil structure.  We suggest that a comprehensive revision of Soil Taxonomy is needed that (1) improves internal consistency in definitions and uses of terms, (2) contains shorter definitions and simplified terminology, (3) includes keys that have inclusive, not exclusive, classification criteria, and (4) has unifying concepts with a universal soil classification system.