Soil Morphology and Classification

E horizon
A horizon
B horizon
(Illuvial)
(Elluvial)
C horizon
R horizon
O horizon
Master Horizons
B horizon
Enough information?

Sub-horizon designations

Sub-horizon designations
p – plowing/disturbance
t – clay accumulation
g – gleying
h – illuvial organic matter
w – development of color/structure
o – oxic
Subordinate distinctions within master horizons

Subordinate distinction (p = plowed)
Disturbed surface horizon (cultivation, pasture, forestry)
Used with the A master horizon (e.g. Ap horizon)
Ap horizon

Subordinate distinction (t = clay accumulation)
Translocation of clay or formed in place
Coatings or discrete
Used with the B master horizon (e.g. Bt)
If reduced, can be used with the g sub horizon (Btg)
*

Subordinate distinction (g = gleying)
Oxygen deprived or reduced state due to water saturation.
Reduction of iron (Fe III to Fe II)
low chroma
Often used with B master horizon (Bg horizon), also E and C horizon.
gleyed
material
oxidized
material
oxidized
Fe3+
Fe2+

Subordinate distinction (h = organic accumulation)
Accumulation of illuvial organic matter-metal complexes Coatings on sand and discrete particles
h = “humic”
value and chroma approximately 3 or less
Used with the B master horizon (e.g. Bh horizon)
Bh horizon
“spodic horizon”
*

Subordinate distinction (w = color or stucture)
Non-illuvial development
of color or structure
“w” can = “weak”
Commonly used with the
B master horizon (e.g. Bw)
Bw

Subordinate distinction (o = oxic horizon)
Low activity clays
Few weatherable materials
Little rock structure
Fe and Al oxides

Subordinate distinctions
g – gleying
h – illuvial organic matter
p – plowing/disturbance
t – clay accumulation
w – development of color/structure
o – oxic

Subordinate distinctions and Organic Matter

Subordinate distinction (a, e, i)
Denotes the degree of organic matter decomposition
in the O horizon.
Oa – highly decomposed (sapric)
Oe – moderately decomposed (hemic)
Oi – slightly decomposed (fibric)
Sapric –most decomposed, low plant fiber, low water content
Hemic – intermediate decompostion
Fibric – least decomposed, recognizable fibers

Summary
Master: O, A, E, B, C, R
Sub horizon symbols: g, h, p, t, w and a,e,i
Examples: Oa, Oe, Oi
Bt
Bg
Btg
Bw
Ap

Other Designations

Vertical Subdivisions
Characterized by similar master and/or subordinate
properties separated by “degree”.
Bt1
Bt2
Bt3

Transitional Horizons
Transitional layers between master horizons.
AE
EB
BE
Dominant
character
Subordinate
Character

Synthesis
Ap
AE
E
Bh
Btg1
Btg2

Soil Taxonomy

Soil Classification/Taxonomy
Based on soil profile characteristics and
the concept of soils as a natural body.
Observable properties: color, texture, structure,
pH, O.M…
Soil Profile
Hierarchical
Genesis
1883 V.V. Dukachaev: climate, vegetation, soil
1927 C.F. Marbut (USDA) applied to U.S. (1965)

Soil Classification/Taxonomy
Adamsville: Hyperthermic, uncoated Aquic Quartzipsamment
USDA classification system
Soil Survey Staff 1965
Soil Taxonomy published 1975

Order
Suborder
Great group
Sub group
Family
Series
12
19,000
Soil Taxonomy Hierarchy
63
250
1400
8000
Kingdom
Phylum
Class
Order
Family
Genus
Species

Units for Soil Classification
Pedon – smallest three-dimensional unit that displays
the full range of properties characteristic of
a given soil. (1-10 m2 of area)
- the fundamental unit of soil classification
Polypedon – group of closely associated pedons in the field
Soil Series – class of soils world-wide which share a common
suite of soil profile properties

Soil Sampling Units

Diagnostic Horizons
Surface
Subsurface

Diagnostic Surface Horizons
Epipedons
Mollic
Umbric
Ochric
Histic
Melanic
Plaggen
Anthropic

Mollic
Histic
Umbric
Ochric
Melanic
Plaggen
Anthropic
X
X
X
X
X = Florida
Diagnostic Surface Horizons

Mollic Epipedon
Thickness > 18-25 cm
Color value < 3.5 moist
chroma < 3.5 moist
Organic Carbon > 0.6 %
Base Saturation > 50 %
Structure strongly developed
Organic carbon = organic matter x 0.5

View Tim Kiser's map
Taken in Elkhart, Iowa (See more photos here)
41°27' 04" N, 93°31' 52" W41.451073-93.530988

Umbric Epipedon
Meets all criteria of the Mollic epipedon,
except base saturation < 50%
Chemically different than Mollic

Ochric Epipedon
Too: thin
light
low in O.M
Mollic
Umbric
Ochric = pale
Extremely common

Histic Epipedon
Organic horizon
Formed in wet areas
Black to dark brown
Low bulk density
20-30 cm thick
Organic = > 20% - 35% O.M.
(water saturation, clay content)

Melanic Epipedon
Similar in properties to Mollic
Formed in volcanic ash
Lightweight, Fluffy

Anthropic Horizon
Resembles mollic
(color, o.m.)
Use by humans
Shells and bones Water from humans

Plaggen Epipedon
Produced by long-term (100s yrs.) manuring
Old, human-made surface horizon
Absent in U.S.
> 50 cm thick

Diagnostic Surface Horizons
Epipedons
Mollic
Umbric
Ochric
Histic
Melanic
Plaggen
Anthropic
Very common
Human-derived
“specialized”

Vegetation
established
O.M. accumulation
time
Organic Matter Accumulation
Parent
material
tmax = 3000 yrs

Diagnostic Sub-surface Horizons

Diagnostic Subsurface Horizons
Clays Organic Matter Oxides
Formation
Translocation
Transformation

Organic Matter Clays Oxides
smectites
Subsurface Horizons
Kaolinite
Also: salts, carbonates, sulfides
Dark colors
Metals (Fe, Al)
Iron
Aluminum
Formation
Translocation
Transformation

Diagnostic Subsurface Horizons
Albic
Argillic
Spodic
Oxic
Cambic
Kandic
Sombric
sulfuric
Natric
Agric
Calcic
Gypsic
Salic
Duripan
Fragipan
Placic
Sub-Horizon Designations

Diagnostic Subsurface Horizons
Albic (white) Horizon
Light-colored (Value > 6 moist )
Elluvial (E master horizon*)
Low in clay, Fe and Al oxides
Generally sandy textured
Low chemical reactivity (low CEC)
Typically overlies Bh or Bt horizons
albic
*not all E horizons are albic horizons

Argillic Horizon
Illuvial accumulation of silicate clays
Illuvial based on overlying horizon
Clay bridges
Clay coatings
Diagnostic Subsurface Horizons

Diagnostic Subsurface Horizons
Argillic Horizon
Kandic Horizon
Activity of Clays
High
Low
Illuviation of clay
Necessary
Not Necessary

Diagnostic Subsurface Horizons
Spodic Horizon
Spodic
Illuvial accumulation of organic matter
and aluminum (+/- iron)
Dark colored (value, chroma < 3)
Low base saturation (acidic)
Formed under humid acid conditions

Elluviation (E horizon)
Organic matter
Clays
Spodic horizon
Bh horizon
Bt horizon
Argillic horizon
Elluviation and Illuviation
A
E
Bh
A
Bt
E

Diagnostic Subsurface Horizons
Oxic horizon
Highly weathered (high temperatures, high rainfall)
- High in Fe, Al oxides
- High in low-activity clays (kaolinite < smectite < vermiculite)
activity

Albic
Kandic
Argillic
Spodic
Oxic
Diagnostic Horizons
Mollic
Umbric
Ochric
Histic
Melanic
Plaggen
Anthropic
Epipedons
Subsurface