Classification and distribution of soils with albic horizons in the USA: A preliminary analysis

Abstract

The albic horizon, a diagnostic subsurface horizon that is comprised of primary sand and silt particles that are light-colored because they lack clay or iron oxide coatings, is unique in that it is an eluvial horizon that is defined on the basis of a loss rather than a gain of weathering products. Over 3000 official soil descriptions were examined in the US Natural Resources Conservation Service databases to identify which taxa contain albic horizons. Albic horizons are present (i.e., more than 8 soil series) in seven orders, 28 suborders, 73 great groups, and about 1600 soil series in soil taxonomy. Orders with albic horizons can be ranked on an area basis: Alfisols>Spodosols>Ultisols>Mollisols>Inceptisols, Entisols>Aridisols. The mean thickness of the albic horizon is 19cm, with the greatest thickness in Alorthods (90cm) and the least in Xerolls (3.1), Humods (4.0), and Ustolls (5.6cm). Albic horizons may occupy one or two of several positions in the soil profile, including (i) the mineral soil surface, (ii) below an A horizon, (iii) as a buried horizon, (iv) between a variety of diagnostic subsurface horizons in bisequal soils, and (v) in some soils with alternating E and Bt lamellae. Albic horizons separate or are underlain mainly by an argillic or a spodic horizon. Half (50%) of the soils with albic horizons are excessively to well drained. Many albic horizons have been lost due to cultivation, especially in Aqualfs, Udalfs, and Udults.