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Correlations of BCI soils

Table 5.6 extracts the elements of the Catapan (1970) multi-attribute coding system that are relevant to the soils of BCI.  The Catapan codings for the BCI soil classes (Table 5.7) do not include agricultural land capability, as it is irrelevant for a dedicated and protected research forest.

BCI applicable elements of Catapan (1970) coding system


Epipedon (topsoil) type


Diagnostic subsoil horizon









O = ochric
U =umbric
M = mollic

T = argillic
C = cambic
X = oxic

W = well
M = moderate
N = imperfect
P = poor

F = fragmental
Kc = clay skeletal
Lf = fine loam
Cf = fine clay
Cv = very fine clay

1 = very deep
4 = very shallow














Agricultural constraints







i = zero
vii = very severe

E = volcanic
M = marine

A = 0 – 3%
E = 45 – 75
F = 75+

1 = slight
2 = severe

0 = zero & slight
1 = severe
2  = very severe

Parent material

Slope gradient







Catapan (1970) coding of BCI soils


Soil form


Soil classes

Catapan (1970) coding

Deep red light clay

Ava, Harvard, Balboa

O  X  W  Cf/Lf  1
E  A/B  1  0


O  X  W  Cf/Lf  1
M  A/B  1  0

Shallow red light clay


O  C  W  Kc/Cf/Lf  2/4
E  B/E  1  1

Deep brown fine loam


O  X  W  Cf/Lf  1
E  A/B  1  1

Shallow brown fine loam

Marron, Hood, Standley

O  C  W  Kc/Cf/Lf  2/4
E  B/E  1  1


O  C  W  Kc/Cf/Lf  2/4
M  B/E  1  1

Dark fine loam


U/M  C  W  Kc/Cf/Lf  2/4
M  B/E  1  1

Miller, Nemesia (+ some Marron & Hood)

U/M  C  W  Kc/Cf/Lf  2/4
E  B/E  1  1

Pale swelling clay

Barro Verde

U  T  N  Cf/Cv  1
M  A/B  1  0

Pale swelling clay with reddish brown upper subsoil


O  T  N  Cf/Cv  1
M  A/B  1  0

Lake, Barbour, Gross

O  T  N  Cf/Cv  1
E  A/B  1  0

Mottled heavy clay

Lutz, Weir

O  T  N  Cf/Cv  1
M  B/E  1  1

Swamp gleys


U  T  G  Lf/Cf  1
E  A  1  1


International correlations

A disadvantage of locally defined soil classes is that they are not known outside their home range. For international communication and comparisons, the BCI classes need to be correlated with widely known soil taxa and names.  Table 5.9 correlates BCI soils with taxa in the two main international systems of classification; the FAO World Reference Base (WRB) for Soil Resources (FAO, 1998; Deckers et al., 2005), and the USDA Soil Taxonomy (ST) (Soil Survey Staff, 1999 & 2006).

The correlations are tentative for the present, because both systems require identification of argic (WRB), argillic/kandic (ST) horizons as an early step in their pauci-thetic multi-level hierarchies.  Argic/argillic horizons are defined on substantial, systematic and sharp increases in clay content with depth, i.e. > 20% proportional increase in clay over a depth interval of < 30 cm.  ST additionally requires argillic horizons to have morphological indications of vertical argilluviation, especially clayskins on the faces of soil structural units.  These are desirable, but not mandatory, features of argic horizons in WRB.

As discussed Appendix A, laboratory determination of clay content is problematic in well-aggregated oxidic clays. We therefore base our identification of argic/argillic horizons on field textures and clayskins. These indicate that there are clay increases with depth in most of the deeper and more mature soils on BCI, but these are often too attenuated and have insufficient clayskins (Fedoroff & Eswaran, 1985) to be unequivocally argic/argillic.

The subsoils of the BCI red light clays are therefore designated as ferralic (WRB) or oxic (ST) horizons, and these soils are correlated with the Ferralsols (WRB) or Oxisols (ST).  Some subsoils are marginally argic/argillic and the textural profiles are transitional to the Luvisols, Acrisols, Lixisols or Alisols in WRB and Ultisols or Alfisols in ST.  Borderline argic/argillic reddish clays and fine loams are extensive in many parts of the humid tropics (Baillie, 1996; Kaufmann et al., 1998), such as the wet zone of Sri Lanka (Leinweber et al.,1998 ;Mapa et al., 1999), and Indonesia  (Soepartohardjo & Ismangun, 1985).  The residual lava flow soils at the La Selva research forest in Costa Rica appear to have similarly equivocal argic/argillic subsoils, and were originally designated as Ultisols (Sollins et al., 1994), but have since been re-assigned to the Oxisols (Schwendenmann et al., 2003). This kind of uncertainty complicates classification of many tropical soils (Sombroek & Siderius, 1981), and is why we did not use either of the international systems for the primary classification of BCI soils.

For soils with clay increases that are sharp enough to be argic, WRB has four main groups differentiated on clay activity and base saturation (Table 5.8).   WRB explicitly permits the use of group names as adjectival qualifiers (Deckers et al., 2005) of other groups.  We use the argic group names to subdivide the BCI Ferralsols on clay activity and base status (Table 5.9 and Appendix B).
ST makes similar distinctions on clay activity and base status in soils with argillic horizons (Table 5.8).  ST makes a further distinction between profiles with a clay ‘step’, in which clay contents stay high from the argillic horizon downwards (‘pale-’), and those with a distinct mid-profile clay  ‘bulge’, below which there is a systematic decrease from the clay maximum (‘hapl-‘). Field textures indicate that most clay increases in the BCI clays are paleargillic steps.  We use elements from the ST argillic group names as qualifiers of the Oxisols in Table 5.9 and for individual profiles in Appendix B.

The ST suborder names include the element ‘ud’, based on soil moisture regime (SMR). Although the atmospheric climate of BCI has a dry season of over three months in many years, the soils do not dry out immediately after the cessation of rain, and are rarely at wilting point for more than 90 days cumulative p.a. (Andrade, et al., 2005; Jackson et al., 1995; Meinzer et al., 2004), so the SMR of BCI is udic rather than ustic.  Soil temperature regime (STR) is a criterion at fifth and lower (family and series) levels in ST. STR for BCI are isohyperthermic, but we are not correlating to that level at present.

Base status and clay activity criteria and taxa in WRB & ST



Base saturation

Clay activity

ECEC > 16 clay

ECEC < 16 clay

WRB (FAO, 1998)

BS> 50%



BS< 50%

Alisol Acrisol
ST  (Soil Survey Staff, 2006)

BS > 50%


Paleudalf Kandiudalf

BS< 50%


Paleudult Kandiudult


The seasonal cracking, microgilgai, and predominance of smectitic clay minerals show that the pale swelling clays have vertic tendencies. However, their subsoils lack the slickensides and wedge structures required for true vertisols (same name in both systems).  They are therefore correlated as transitional vertic subgroups of taxa defined on clear clay increases, restricted drainage, and base saturation.  The high base saturation of Barro Verde correlates it as Hapludertic (ST).  The low bases and high extractable Al of Zetek and the other BCI pale swelling clay classes are equivalent to the Dystrudertic (ST) subgroup

The brown and red fine loams are correlated as Cambisols (WRB)/Inceptisols (ST) on the basis of their shallow depth, limited weathering, pedogenic immaturity and high base status.  The dark fine loams are their mollic (WRB)/humic (ST) counterparts.

Swamp soils are correlated with Gleysols (WRB) and Aquic suborders of the Inceptisols and Entisols (ST) on the basis of their restricted drainage


Provisional international correlations of BCI soils

BCI soil form

BCI soil classes

World Reference Base of Soil Resources (FAO, 1998)

Soil Taxonomy subgroup     (Soil Survey Staff, 2006)

Shallow brown shallow and stony fine loam

Marron, Hood, Standley, Wetmore

Leptic & Eutric Cambisol

Lithic & Typic Eutrudept

Deep brown fine loam


Hypereutric & Haplic Ferralsol

Typic Eutrudox, Hapludox & Kandiudox

Shallow red light clay


Leptic & Ferralic Cambisol

Lithic & Typic Eutrudept

Dark fine loam

Miller, Oscuro (+ some Marron & Hood)

Leptic & Mollic Cambisol

Lithic Humic & Humic Eutrudept

Deep red light clay

Ava, Harvard, Balboa, Poacher

(Luvic, Alumic, Lixic and Acric)  Hypereutric & Haplic Ferralsol

Typic (& Paleudalfic, Kandiudalfic Paleudultic, or Kandiudultic) Eutrudox, Hapludox & Kandiudox

Pale swelling clay

Barro Verde

Vertic Luvisol & Vertic Eutric Gleysol

(Hapludertic) Paleudalf & Epiaqualf

Pale swelling clay with reddish brown upper subsoil

Zetek, Lake, Barbour, Gross

Vertic Alisol & Vertic Alumic Gleysol

(Dystrudertic) Paleudult & Epiaquult

Mottled heavy clay

Lutz, Weir

Ferric Cambisol

Aquic Lithic Eutrudept



Mollic, Eutric & Haplic Gleysol

Lithic, Mollic & Typic Endoaquept & Endoaquent