Mollic Epipedon - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 37

None of the 59 soil series in the Oxisol order in the USA, which are confined to
Hawaii (HI), Puerto Rico (PR), and Micronesia, contain a mollic epipedon.
According to Beinroth et al. ( 1996 ), some Oxisols in tropical regions have a mollic
epipedon. Four soil orders lack soils with a mollic epipedon, including the Histosols
(organic soil materials), Aridisols (too dry), and the Spodosols and Ultisols (too
acidic or base depleted).
These findings suggest that Mollisols contain 91 % of the mollic epipedons or
intergrades in soil series identified in the USA, followed by Alfisols (4.8 %),
Entisols and Andisols (1.0 % each), and Inceptisols (0.3 %; Table 5.2 ). Soils with
a mollic epipedon comprise about 41 % of the total soil series (approximately
23,000) identified in the USA.
5.4 Distribution of Soils with a Mollic Epipedon
Soils containing a mollic epipedon occur in all of the states except three in New
England (Delaware, DE; New Hampshire, NH; and Rhode Island, RI), total about
8,250 series, and comprise 3.27 million km 2 or 39 % of the US area (Fig. 5.2 ).
Fig. 5.2 Distribution of Mollisols in the USA. Soils in other orders with a mollic epipedon are not
shown (Figure courtesy of USDA, NRCS)