Chapter 16: Correlation of Canadian Soil Taxonomy with Other Systems

The approximate equivalents of the soil horizons and taxa in the Canadian system are given for the U.S. system (Soil Survey Staff 1994) and in the terminology of the FAD-UNESCO soil map of the world (Food and Agriculture Organization of the United Nations 1985). The horizon designations and terms are rarely exactly equivalent. The definitions of soil horizons and soil taxa differ from one system to another.

The U.S. system includes a category named suborder that is not in the Canadian system, and the FAO soil units are arranged into only two categories. Thus the categorical levels of the related taxa are generally not equivalent. The closest approximation to equivalence of taxa is in the case of Organic soils (Canadian) and Histosols (U.S.). Great groups and subgroups of Organic soils are nearly equivalent to the corresponding suborder and great groups of Histosols. This correspondence resulted from United States and Canadian pedologists working together to develop taxonomy for Organic soils. However, even in this case there are differences. For example, the organic matter content required for Histosols differs somewhat from that required for soils of the Organic order.

In other orders, differences in the approximately equivalent taxa are greater. For example, most Chernozemic soils are Mollisols, but some are Aridisols. Many Mollisols are Chernozemic soils, but some are Gleysolic soils, others are Solonetzs, and still others are Melanic Brunisols. There are also basic differences between Podzolic soils and Spodosols. Most Podzolic soils are Spodosols, but a significant proportion are Inceptisols because a spodic horizon must be dominated more by amorphous material than a Podzolic B horizon. Conversely, a few Podzolic Luvisols are Spodosols. All Vertisolic soils would qualify as Vertisols. However, all Vertisols would not be Vertisolic because Vertisolic soils must have a layer affected by argillipedoturbation as well as slickensides and cracks. At lower levels in the systems, differences become progressively greater.

Tables 6, 7, and 8 provide some idea of how soil horizon designations and soil taxa are related at the upper levels in the three systems. The tables have been revised from those prepared by J.S. Clayton for previous editions of the Canadian System of Soil Classification. Revisions were required because of some changes in horizon designations and in the definitions of horizons and taxa in both the Canadian and U.S. systems. Correlation at the subgroup level is not presented.

The tables are not adequate for correlating either the horizon designations or the taxonomy of a given pedon as expressed in one system with those of another system. Adequate correlation requires knowing the criteria and definitions in the systems involved.

Table 6 Correlation of horizon definitions and designations
1. Canadian 2. U.S. 3. FAO Comments
* 17% organic C equals about 30% organic matter.
** Fep: Fe extractible in pyrophosphate
O O H 1 (Can. Limit): organic horizon (O) >17% organic C. *
2 & 3 (U.S. and FAO limits): lower limit of organic horizons ranges proportionately from 20% OM with 0% clay to 30% OM with >50% clay
Of Oi H 1 (Can. Limit): organic horizon (O) >17% organic C. *
2 & 3 (U.S. and FAO limits): lower limit of organic horizons ranges proportionately from 20% OM with 0% clay to 30% OM with >50% clay
Om Oe H 1 (Can. Limit): organic horizon (O) >17% organic C. *
2 & 3 (U.S. and FAO limits): lower limit of organic horizons ranges proportionately from 20% OM with 0% clay to 30% OM with >50% clay
Oh Oa H 1 (Can. Limit): organic horizon (O) >17% organic C. *
2 & 3 (U.S. and FAO limits): lower limit of organic horizons ranges proportionately from 20% OM with 0% clay to 30% OM with >50% clay
Oco Oa H Coprogenous limnic material
L-F Oi-Oe O Generally not saturated with water for prolonged periods
L-H Oi-Oa O ---
F-H Oe-Oa O ---
A A A 1: ≤17% organic C;
2 & 3: upper limit of OM ranges proportionately from 20% OM with 0% clay to 30% OM with clay >50%
Ah A Ah 1: ≤17% organic C;
2 & 3: upper limit of OM ranges proportionately from 20% OM with 0% clay to 30% OM with clay >50%
Ahe AE (Ah-E) 1: ≤17% organic C;
2 & 3: upper limit of OM ranges proportionately from 20% OM with 0% clay to 30% OM with clay >50%
Ae E E ---
Ap Ap Ap ---
AB AB or EB AB or EB Transitional horizons
BA BA or BE BA or BE ---
A & B A & B A/B Interfingered horizons
AC AC A/C ---
B B B ---
Bt Bt Bt ---
Bf Bs Bs 1: specific limits; 2 & 3: no specific limit
Bhf Bhs Bhs 1: >5% organic C
Bgf Bgs Bgs ---
Bh Bh Bh 1: Specific C to Fep ratio; 2&3: no specific C to Fep ratio
Bn Bn Bn ---
Bm Bw Bw ---
C C C ---
IIC 2C IIC ---
R R R ---
W --- --- Water
other suffixes May be used with A, B, or C horizons
b b b 1 & 2: buried; 3: buried or bisequa
c m m ---
ca k k Accumulation of carbonates
--- y y Accumulation of gypsum
cc m c ---
g g g or r 3: g - mottling, - strong reduction
j --- --- ---
k --- --- Indicates presence of carbonate
--- v --- Plinthite
--- q q Silica accumulation
s z z Visible salts
ss ss --- Indicates presence of slickensides
sa y or z y or z 1: includes gypsum;
2 & 3: y - gypsum, z - other more soluble salts
--- o --- Residual sequioxide concentration
u --- --- Turbic
--- --- u Unspecified
v --- --- Vertic Horizon
x x x Fragipan
y --- --- Cryoturbation
z f I Permafrost layer

Table 7 Correlation of United States and Food and Agriculture Organization of the United Nations diagnostic horizons with nearest Canadian equivalents
1. U.S. 2. FAO 3. Canadian Comments
Mollic Epipedon Mollic A Chernozemic A With high base status
Anthropic Epipedon Mollic A Cultivated Chernozemic A ---
Umbric Epipedon Umbric A Ah With low base status
Histic Epipedon Histic H Of, Om, Oh ---
Ochric Epipedon Ochric A light-colored A ---
Plaggen Epipedon --- Ap ---
Albic horizon Albic E Ae ---
Argillic horizon Argillic B Bt ---
Agric horizon Argillic B Illuvial B Formed under cultivation
Natric horizon Natric B Bn or Bnt ---
Spodic horizon Spodic B podzolic B ---
Cambic horizon Cambic B Bm, Bg, Btj ---
Oxic horizon Oxic B --- ---
Duripan m c ---
Durinodes --- cc ---
Fragipan x Fragipan ---
Calcic horizon Calcic horizon Bca or Cca ---
Petrocalcic Bkm Bcac or Ccac ---
Gypsic Gypsic Asa, Bsa, Csa 3. Only if sa horizon is dominantly CaSO4
Salic --- Asa, Bsa, Csa ---
Placic Thin iron pan Placic ---
Plinthite Plinthite --- ---
Lithic contact --- Lithic contact ---
Paralithic contact --- IICc ---
g Gleyic horizon g ---
--- sulfuric horizon --- Low pH, jarosite mottles

Table 8 Taxonomic correlation at the Canadian order and great group levels [1]
Canadian System U.S. Soil Taxonomy WRB(FAO) [2] System
[1] Only the nearest equivalents are indicated
[2] World Reference Base for Soil Resources (Deckers et al. 1998)
Chernozemic Borolls Kastanozem, Chernozem, Greyzem, Phaeozem
Brown Chernozem Aridic Boroll subgroups Kastanozem (aridic)
Dark Brown Chernozem Typic Boroll subgroups Kastanozem (Haplic)
Black Chernozem Udic Boroll subgroups Chernozem
Dark Grey Chernozem Boralfic Boroll subgroups, Albolls Greyzem
Solonetzic Natric great groups, Mollisols & Alfisols Solonetz
Solonetz Natric great groups, Mollisols & Alfisols Mollic, Haplic, or Gleyic Solonetz
Solodized Solonetz Natric great groups, Mollisols & Alfisols Mollic, Haplic, or Gleyic Solonetz
Solod Glossic Natriborolls, Natralbolls Solodic Planosol
Vertic Solonetz Haplocryerts Sodic Vertisol
Luvisolic Boralfs & Udalfs Luvisol
Gray Brown Luvisol Hapludalfs or Glossudalfs Albic Luvisol, Haplic Luvisol
Gray Luvisol Boralfs Albic Luvisol, Gleyed Luvisol
Podzolic Spodosols, some Inceptisols Podzol
Humic Podzol Cryaquods, Humods Humic Podzol
Ferro-Humic Podzol Humic Cryorthods, Humic Haplorthods Orthic Podzol
Humo-Ferric Podzol Cryorthods, Haplorthods Orthic Podzol
Brunisolic Inceptisols, some Psamments Cambisol
Melanic Brunisol Cryochrepts, Eutrochrepts, Hapludolls Cambisol, Eutric Cambisol
Eutric Brunisol Cryochrepts, Eutrochrepts Eutric Cambisol, Calcic Cambisol
Sombric Brunisol Humbric Dystrochrepts Dystric Cambisol, Umbric Cambisol
Dystric Brunisol Dystrochrepts, Cryochrepts Dystric Cambisol
Regosolic Entisols Fluvisol, Regosol
Regosol Entisols Regosol
Humic Regosol Entisols Fluvisol, Regosol
Gleysolic Aqu-suborders Gleysol, Planosol
Humic Gleysol Aquolls, Humaquepts Mollic, Umbric, Calcic Gleysol
Gleysol Aquents, Fluvents, Aquepts Eutric, Dystric Gleysol
Luvic Gleysol Argialbolls, Argiaquolls, Aqualfs Planosol
Organic Histosols Histosol
Fibrisol Fibrists Histosol
Mesisol Hemists Histosol
Humisol Saprists Histosol
Folisol Folists Histosol
Cryosolic Gelisols Cryosol
Turbic Cryosol Turbels Cryosol
Static Cryosol Orthels Cryosol
Organic Cryosol Histels Cryic Histosol
Vertisolic Cryerts Vertisol
Vertisol Haplocryerts Calcic Vertisol, Eutric Vertisol
Humic Vertisol Humicryerts Dystric Vertisol

Source: The Canadian System of Soil Classification (Third Edition)