Mollic Epipedon - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 40

Table 5.4 (continued)
Area Soil taxa Role of soil-forming factor Citations

Topography

Iran Argixerolls,

Mollic
Hapludalfs

Mollic epipedon forms on summit and
toeslope and not on more eroded
backslope and footslope

Khormali and
Ajami ( 2011 )

Time

Upper
Mississippi V.

Mollisols Many Mollisols developed during the

“climatic optimum” 6-4 ky ago

Smith et al. ( 1950 )

Pennsylvania Udolls Many Mollisols developed during the

Hypsithermal 7-3 ky ago

Waltman and
Ciolkosz
( 1995 )

Craters of the
moon, ID

Xerolls Mollisols require 14 ky yr of loess

deposition to develop on lava flows

Vaughan
et al. ( 2011 )

Southern IL Udolls Mollic epipedon formed in 550 yr Olson et al. ( 2005 )

WI Mollic

Hapludalfs

Mollic epipedon formed in 265 yr Nielsen and Hole

( 1963 )

IA Argiudolls Mollic epipedon formed in 400 yr Arnold and

Riecken ( 1964 )

Alfisols (18 %); alluvium was present in 59 % of the Entisols, 27 % of the
Inceptisols, 24 % of the Alfisols, and 14 % of the Mollisols; and lacustrine
sediments were the initial materials for Inceptisols (38 %), Entisols (29 %), and
Vertisols (16 %). Vertisols were derived from colluvium and residuum; and
Andisols originated from volcanic ash and cinders. The source of base cations in
Andisols likely is dry deposition (Vaughan et al. 2011 ).
Parent materials yielding mollic epipedons include residuum from basalt
(Bhattacharyya et al. 2006 ; Vaughan et al. 2011 ), limestone (Mella and Mermut
2010 ), and marl (Shaw and Rabenhorst 1999 ), as well as calcareous loess and till
(Fenton 1983 )(Table 5.4 ). Base-forming cations, such as Ca, K, and Mg, are released
by weathering and mineralization of SOM and cycled by grassland or deciduous
forest vegetation. However, atmospheric deposition may be a source of these base
cations. In a study of wetfall deposition in continental USA, the highest area-
normalized total wet deposition of Ca 2+ was in Alfisols (172 kg of Ca 2+ km 2 )and
Mollisols (170 kg of Ca 2+ km 2 )(Goddardetal. 2009 ). Mollic epipedons also may be
influenced locally by dry deposition (Mella and Mermut 2010 ;Andreevaetal. 2011 ).
The time factor has received some attention in the literature. Mollisols may have
formed in the USA during the “climatic optimum” or Hypsithermal Interval about
6,000-4,000 yr ago (Smith et al. 1950 ; Waltman and Ciolkosz 1995 ). In semiarid
Idaho, Mollisols require 14000 yr to develop from loess overlying lava flows
(Vaughan et al. 2011 ). However, the mollic epipedon may form in as little as
200-400 yr (Table 5.4 ).
Fires may be involved in the distribution of soils with mollic epipedons
(Rodionov et al. 2010 ). It is of interest that 11 to 33 % of soils with a mollic
epipedon no longer were classified as Mollisols after 50 yrs of intensive agriculture
(Veenstra and Burras 2012 ).