Historical development of soil and weathering profile concepts from Europe to the United States of America

In the 1870s, agricultural geologists (pioneer pedologists) in Germany, Denmark, and Russia conceived of the soil profile. In more than a century since, pedologists have generally agreed on the reasons and purpose for using symbols such as A-B-C for the designations, but not on the definitions themselves or the assigned significance of the designations. In this paper, we submit that two seemingly conflicting classes of profile concepts evolved in the USA from European roots. The conflict stems historically from arbitrarily defined thin and thick profile concepts, often referred to as the soil or geologic weathering profiles, respectively. The pedologic or thin profile concept is depth-restricted when compared with the geologic thick weathering profile. The geologic profile concept was developed as a homologue of the pedologic profile and is considered to be the full or complete profile of weathering. Throughout the 20th century many variations of the concept of profile appeared, and all seem to have pedo-geo conflicts, exemplified by the myriad C horizon definitions by soil scientists. Recent concepts, such as the pedoweathering profile, have integrated the terminology used by pedologists and geologists into a functional and useful classification for all horizons of complete profiles. Full 21st century understanding of soils beyond the historic 20th century needs of agriculture, increasingly requires a knowledge of soil properties to greater depth than merely the historic solum and upper C horizon, and makes understanding subsolum properties more critical than ever before.