1. Soil Morphology and Classification

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

3. Sub-horizon designations

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

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

6. 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) *

7. 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.
oxidized
material
Fe3+
oxidized
Photographs showing redoximorphic features (soil mottling) which are color patterns in the soil formed by the oxidation and reduction of iron and/or manganese caused by saturated conditions within the soil. Redoximorphic features are used to estimate the depth to seasonal high watertable
gleyed
material
Fe2+

8. 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”

9. 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

10. Subordinate distinction (o = oxic horizon)
Low activity clays
Few weatherable materials
Little rock structure
Fe and Al oxides
The oxic horizon has:           a. a CEC7  < 16cmol(+)/kg of clay and an ECEC < 12 cmol(+)/kg of clay which is due to the low activity clay minerals (1:1 clays, Fe and Al oxides, etc)           b.  < 10% weatherable minerals in the sand fraction           c.  < 5% rock structure

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

12. Subordinate distinctions and Organic Matter

13. 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

14. Sub horizon symbols: g, h, p, t, w and a,e,i
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

15. Other Designations

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

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

18. Synthesis Ap AE E Bh
Btg1
Btg2

19. Soil Taxonomy

20. Soil Classification/Taxonomy
Hierarchical
Soil Profile
Based on soil profile characteristics and
the concept of soils as a natural body.
Observable properties: color, texture, structure,
pH, O.M…
Genesis
1935, 1949,1965 comprehensive and shared by 43 other countries,
V.V. Dukachaev: climate, vegetation, soil
1927 C.F. Marbut (USDA) applied to U.S. (1965)

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

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

23. 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

24. Soil Sampling Units
Malabar Series

25. Diagnostic Horizons
Surface
Subsurface

26. Diagnostic Surface Horizons
Epipedons
Mollic
Umbric
Ochric
Histic
Melanic
Plaggen
Anthropic

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

28. 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

29. 41°27' 04" N, 93°31' 52" W
Taken in Elkhart, Iowa (See more photos here)
View Tim Kiser's map

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

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

32. 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)

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

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

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

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

37. Organic Matter Accumulation
O.M. accumulation
Histic
Mollic, Umbric
ochric
time
Parent
material
Vegetation
established
tmax = 3000 yrs

38. Diagnostic Sub-surface Horizons

39. Diagnostic Subsurface Horizons
Formation
Translocation
Transformation
Clays Organic Matter Oxides

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

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

42. 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

43. Diagnostic Subsurface Horizons
Argillic Horizon
Illuvial accumulation of silicate clays
Illuvial based on overlying horizon
Clay bridges
Clay coatings
Accumulation based on absolute increases compared to relevant horizon above or below. Argillic horizon. An argillic horizon is an illuvial horizon in which layer-silicate clays have accumulated to a significant extent by illuviation. They have formed below the surface of a mineral soil but may be exposed at the surface by erosion. In general, this is a B horizon which has an increase in clay content of at least 1.2 times that of the eluvial horizon above and is, in general, parallel to the surface of the polypedon. This increase of 20% in clay content occurs most in soils within a vertical distance of less than 30 cm. In case of clayey soils, this requirement would be unreasonable. If the surface horizon is greater than 40% clay, the increase of clay needed is only 8%. For sandy soils with less than 15% clay, an increase of 3% is required for meeting the criteria of an argillic horizon. In other words, if the clay content of the eluvial horizon is between 15 and 40%, an increase in clay of 20% is needed to meet the requirements for an argillic horizon.

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

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

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

47. 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

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

49. Soil Taxonomy Diagnostic Epipedons Diagnostic Subsurface horizons
Moisture Regimes
Temperature Regimes