Geoscience Reference
In-Depth Information
Table 7.3 Influence of soil-forming factors on development of the ochric epipedon
Area
Factor
References
Climate
TX;
So. Africa
Ochric forms in drier soils and mollic in wetter
Aide and Smith (
2001
)
and Van Huyssteen
et al. (
2009
)
Argentina
Regression model: mean annual precipitation correlated
with ochric
Bravo et al. (
2007
)
Organisms
NW CA
Soil-vegetation controls influence SOM levels and
epipedons: ochric under conifer forest and mollic
under prairie and broad-leaved
Popenoe et al. (
1992
)
Relief
Brazil
Histic forms in wet depressions and ochric in dry uplands Schiavo et al. (
2012
)
precipitation was less than 300 mm and mollic epipedons in Mollisols where the
mean annual precipitation ranged from 300 to 400 mm. Popenoe et al. (
1992
)
illustrated the importance of vegetation in influencing SOC levels, reporting ochric
epipedons are conifer forest and mollic epipedons under prairie and broad-leaved
forest in northwest CA. In Brazil, histic epipedons formed in wet depressions and
ochric epipedons in dry uplands (Schiavo et al.
2012
).
7.6 Genesis of Soils with an Ochric Epipedon
The ochric epipedon forms in soils where the combined soil-forming factors do not
allow sufficient SOC accumulation to form an umbric, mollic, or histic epipedon.
7.7 Summary
The ochric epipedon fails to meet the requirements of other diagnostic epipedons
because it is too thick, contains too little SOC, or contains light soil colors. The
ochric epipedon likely occurs in more than 56 % of the soil series and soil area of
the USA. The ochric epipedon is common in six soil orders: the Alfisols, Aridisols,
Entisols, Inceptisols, Oxisols, and Ultisols. Key soil-forming factors contributing to
the formation of ochric epipedons include excessively drained uplands, a dry soil
climate, and the lack of grassland or deciduous forest. The genesis of soils with an
ochric epipedon is dominated by processes that do not contribute to thick, organic-
enriched soils.
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