Lecture 5a
Soil Taxonomy




Purpose of Soil Taxonomy:
1. Organize knowledge about soils
2. Understand relationships among different soils
3. Establish groups or classes for practical
purposes.




a. predicting behavior
b. identifying best uses
c. estimating productivity
d. extending research results
Soil Taxonomy- 12 Soil Orders


Soils are
classified into
into six
categories based
on diagnostic
characteristics
The last (largest)
category will
place the soils
into one of the
12 Soil Orders.
Soil Taxonomy
Fine-loamy mixed, superactive, mesic Aquic Argiudolls
(This is the name of a specific soil in Soil Taxonomy)
1)
2)
3)
4)
5)
6)
Orders (12)
Suborders (54)
Great Groups (211)
Subgroups (1,100+)
Family (7,000+)
Series (a lot!)
This is the name of one
Of the 12 large categories
Mollisol - oll
Oder - root of order
Orders
Fine-loamy mixed, superactive, mesic Aquic Argiudolls


Highest and most general
of the soil classification
system (similar to the
phylum in plant
taxonomy)
Based on conditions
under which the soil
developed
Order
oll = Mollisols
Suborders
Fine-loamy mixed, superactive, mesic Aquic Argiudolls

Grouped by similarities in
soil formation such as
wetter/dryer soil,
colder/warmer soil, etc.
Sub
Order
Order
Ud = Udic Moisture
Great Groups (not required to know)
Fine-loamy mixed, superactive, mesic Aquic Argiudolls
Sub
Order
Great
Group

Based on differences
between soil horizons
Order
Argi = Clay
accumulation
Sub Groups (not required to know)
Fine-loamy mixed, superactive, mesic Aquic Argiudolls

Describes a profile
characteristic, wetness,
sand, tonguing of E, etc.
Sub
Group
Sub
Order
Great Order
Group
Aquic = wet soil
Family (not required to know)
Fine-loamy, mixed, superactive, mesic Aquic Argiudolls
Family
Texture, clay minerals, CEC, temp,

Based on soil properties that
affect management and root
penetration, such as texture,
temperature, and depth
Sub
Group
Sub
Order
Great
Group
Order
Series = Le Sueur – this is where the soils of the week
names are from – ie Lester, Clarion, Nashwauk etc.
Fine-loamy mixed, superactive, mesic Aquic Argiudolls
Family

Named from the town or landscape
feature near where the soil was
first recognized (Lester = Lester
Prairie, MN. Other examples =
Clarion, Nashwauk, Milaca, Port
Byron, Zimmerman. Le Sueur for Le
Sueur County, MN.)
Sub
Group
Sub
Order
Great
Group
Order
Diagnostics HorizonsUsed to place soils into one of the 12 Soil Orders
Surface
(Epipedon)
 Mollic
 Umbric
 Histic
 Ochric
Subsurface
• Argillic
• Natric
• Spodic
• Oxic
• Cambic
• None
Soil TaxonomyDiagnostic Surface Epipedons





Mollic Epipedon - thick,
dark, soft, surface layer.
Characteristics
Thick - greater than 10
inches; High base
saturation> 50%;
Mineral soil
Soils formed under prairie
vegetation
Other Epipedons



Umbric - like
mollic, but low
base saturation
Histic - Organic
Soil - saturated
with water, > -%
organic matter
Ochric - thin,
light colored surface layers
that do not fit
any of the
above
Base Saturation = relative
amount of bases (Ca, Mg, K)
in the soil,
Low %= few, high% = many
Comparison of Epipedons
Ochric
thinner
Histic
lighter
color
more
organic
matter
Mollic
low base
saturation
Umbric
Diagnostic Subsurface
Horizons


Argillic - illuvial horizon
of clay accumulation Bt
Natric - same as argillic
but with > 15%
exchangeable sodium (Na)
- Btn
Diagnostic Subsurface Horizons

Spodic - illuvial
accumulation of oxides of
Al and Fe (sesquioxides)
and OM, red or dark red
color - only found in acid
sandy soils, with high
rainfall- generally found
below E horizon. Contains a
Bhs or Bs horizon or Bhsm
Oi
E
Bhs
Bs
C
subsurface horizons (cont.)

Oxic - very weathered layer of
only Fe and Al oxides and 1:1 clay
minerals, low pH and not very
fertile (found in tropical soils) Bo

Cambic - slightly altered layer -
not weathered enough to be
argillic, Bw horizon designation or
development of color and or
structure

NONE - no diagnostic subsurface
horizon present
Comparison of Subsurface Diagnostic
Horizons
Spodic
Cambic
less
developed
more Al
and Fe
Argillic
very
weathered
Oxic
more sodium
Natric
12 Soil Orders -
Each Order has a diagnostic epipedon and
subsurface horizons – which could be “none”.
WEB SITE for soil orders = www.mines.uidaho.edu/pses/teach_res












Entisol
Inceptisol
Andisols
Spodosols
Mollisols
Alfisols
Ultisols
Oxisols
Aridisols
Vertisols
Histosols
Gelisols
Entisol - ent


Recent soils - minimal
development, little
horizonation, young
12.5% of world,
Ochric + none
soils.
Entisol - Idaho
A
R
Vertisol - ert

Inverted - soils with high
clay content,

Large shrink swell potential

gradually invert on themselves,

2.1% of the world,

Mollic or Ochric +

none
-
Vertisol = Bss at slickenslide
Inceptisol - ept


Inception - soil shows the beginning
of horizon development, little or no
illuviation,
15.8% of world, Ochric or Umbric +
cambic.
Inceptisol

Soil Formed in
colluvial material in
mountains of Idaho.
Aridisols - id


Arid regions of the
world (19%), < 10 in.
rainfall, usually
carbonates,
Ochric + cambic or
argillic or other
diagnostic feature.
of
contain
A
Bw
Bk
C
Aridisol in Idaho
A
Bt
Bk
Bkqm
R
Aridisol - Nevada

NaCl Salt
accumulates on
the surface and in
the
subsurface.
Az
Bz
C1
C2
Mollisols - oll


soils with thick, dark,
soft surface - mollic +
natric, argillic
high base
- soils of the
9% of the world
cambic,
or none saturation
prairie
Mollisol


This mollisol formed in a new
parent material (loess) that
buried the original soil -the Btb
(b = buried).
Mollisol from Kansas that is
developed in Limestone bedrock.
A1
A2
Bw
BC
R
Spodosols- od


acid sandy soils
with
thick E and red
Bhs ochric and spodic
5.4 % of the
world infertile soils.
Oi
E
Bhs
Bs
C
Alfisol -- alf

fertile forested soils with

saturation (> 35%) forested soils
7% of the world.
ochric and
argillic - high base
Ultisols - ult


soils more weathered
than Alfisols - ochric
and argillic - low base
saturation < 35% - redder
more acid than Alfisols
8.5% of the world - less
than Alfisols
A
E
and
Bt1
Bt2
BC
fertile
Alfisol & Ultisol
Histosols - ist



peat soils - organic
material - histic
0.8% of the world
Histic Epipedon.
Oe1
Oe2
Oe3
Oe4
Oa
2C
Photo USDA
Dyad

Describe the Soil Order that is most likely found in your home town.
Andisols - and


soils from volcanic ash
very light - low bulk density –
1% or the world
A
Bw
Ab
Bwb
Ab’
Andisol from Idaho
A
Bw
2BC
2C
Oxisols - ox


Soils with Oxic horizon - very weathered soils of the tropics. low pH - acid soils high in 1:1 clay minerals
9.2% of world
Oxisol
Ap1
Ap2
Bo1
Bo2
Bo3
Oxisol Puerto Rico
Ap
A
Bo1
Bo2
BC
C
Gelisol - el


New Order as of
1998 - soils with
permafrost (formerly
Cryochrepts - or
frozen Inceptisols)
Cf - horizon
Soil Orders USA
Soil Orders in
Minnesota
Soil Orders – Wisconsin
& Northern Illinois
Soil Suborders of Minnesota








Mollisol - Udoll - Boroll - Aquoll - Ustoll
Alfisol -Udalf - Boralf - Aqualf
Dropped in 1998
Entisol Orthent - Psamment – Aquent
-
Fluvent
Inceptisol - Udept - Aquept
Spodosol - Orthod
Vertisol - Aquert
Histosol - Fibrist - Hemist - Saprist
Suborder definitions






Ud - Udic moisture = moist -southern Mn type
climate & Us = Ustic = Dry
Bor - Boreas = northern Mn. Climate (Frigid
Temperature regime)
Aqu - Aquic moisture = saturated soil - high
water table - Gleyed conditions
Orth - true or simple - regular Entisols &
Spodosols
Psamm - sand - sandy Entisols
Fluv - floodplain –irregular Organic matter
Udoll - Ustoll - Aquoll
Ustoll
Udalf - Boralf - Aqualf
Orthent - Psamment – Aquent Fluvent
Orthent
A
Bw Not Cambic
due to being
too sandy
C


Fluvent – Soils of the
floodplains.
Lots of layers that
are deposited when
the river floods
Orthod
Minnesota Orthod
Wisconsin Orthod
A
E
Bhs
Bs
C
Udept - Aquept
EUTRUDEPTS
Aquert
Fibrist - Hemist - Saprist
Suborder Map
You need to
know the
location of the
suborders in
Minnesota