Geoscience Reference
In-Depth Information
Chapter 21
Sombric Horizon
21.1
Introduction
Diagnostic horizons are the primary building blocks in modern, global soil
taxonomic systems and reflect key soil-forming processes (Lebedeva et al.
1999
).
In many cases, diagnostic horizons result from field and laboratory characterization
of hundreds of pedons and considerable discussion at international workshops.
Examples of subsurface horizons receiving international input include the spodic
horizon in Spodosols (Ahrens and Rourke
2000
), the oxic horizon in Oxisols
(Buol and Eswaran
1988
), and a variety of diagnostic horizons present in Aridisols
(Kimble and Nettleton
1990
). Diagnostic horizons are used at the highest levels in
global soil taxonomic systems, such as
Soil Taxonomy
(ST; Soil Survey Staff
1999
),
the IUSS Working Group WRB (
2007
), and the Russian soil classification system
(Shishov et al.
1997
).
Sombric horizons have not gained the attention that other diagnostic subsurface
horizons have received. For example, we were unable to locate soils with sombric
horizons in electronic databases of the US Department of Agriculture, Natural
Resources Conservation Service (
http://soildatamart.nrcs.usda.gov
) or the ISRIC
World Soil Information Center (
http://library.wur.nl/isric
).
Soils with a sombric
horizon apparently do not occur in the USA or its territories
.
Field and laboratory data were collected from 30 pedons described in the literature
as containing sombric or sombric-like horizons (Sys et al.
1961
;Sys
1972
;Van
Wambeke
1961
,
1992
; Frankart
1983
; Volkoff and Cerri
1987
;Mutwewingabo
1989
;
Faivre
1990
;NizeyimanaandBicki
1992
; Caner et al.
2003
,
2007
; Schaefer
et al.
2002
; Almeida et al.
2009
). These data were evaluated according to criteria
Bockheim, J.G. 2012. Revisiting the definitions of the sombric horizon in Soil Taxonomy and the
World Reference Base for Soil Resources. Geoderma 170:127-135. Acknowledgment is given to
Elsevier Publishers for allowing a revision of this article to be published herein.
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