Mollic Epipedon - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 41

5.6 Genesis of Mollic Epipedons
According to ST, the mollic epipedon is “defined in terms of its morphology rather
than its genesis” (Soil Survey Staff 1999 , p. 23). Nevertheless, the mollic epipedon
later is described as forming mainly from the underground decomposition of
organic residues in the presence of divalent cations such as Ca. An analysis of the
literature revealed surprisingly little recent information regarding the genesis of
Mollisols and the mollic epipedon in particular. Rather, a large body of the recently
published literature deals with the impacts of cultivation and erosion on the SOC
content of Mollisols.
Some of the major theories regarding the formation of Mollisols are synthesized
in a flow diagram (Fig. 5.3 ). Fenton ( 1983 ) discussed the formation of Mollisols,
including the inputs, outputs, transformations, and transfers. He identified melani-
zation (darkening of the soil by addition of organic matter), cumulization (buildup
of the mollic epidedon in toeslope positions), and dust deposition as key inputs,
truncation by erosion and leaching as key outputs, base cycling as a key transfer,
and clay formation as the predominant transformation. Bhattacharyya et al. ( 2006 )
observed that mollic epipedons are formed under a wide range of leaching envi-
ronments, stages of weathering, and horizon differentiation. They considered
Fig. 5.3 Genesis of the mollic epipedon