Soil Orders
Here we go!
Soil Profiles of the
Principal Terrestrial
Soil Types
Figure 3-24
Mosaic of
closely
packed
pebbles,
boulders
Weak humusmineral mixture
Dry, brown to
reddish-brown
with variable
accumulations
of clay, calcium
and carbonate,
and soluble
salts
Desert Soil
(hot, dry climate)
Alkaline,
dark,
and rich
in humus
Clay,
calcium
compounds
Grassland Soil
semiarid climate)
Fig. 3-24a, p. 69
• Ardosol = Desert Soils
• Mollisol = Grassland Soils
Tropical Rain Forest Soil
(humid, tropical climate)
Acidic
light-colored
humus
Iron and
aluminum
compounds
mixed with
clay
Fig. 3-24b, p. 69
Oxisol or Ultisol
•
•
•
•
Form in hot rainy environments.
So what’s the difference Mr. Davis?!
Well, ….
Ultisols are intensely weathered soils of warm and humid
climates. They are typically formed on older geologic
locations in parent material that is already extensively
weathered.
Ultisols have accumulated clay minerals in the B horizon.
While generally low in natural fertility (basic cations, Ca2+,
Mg2+, and K+) and high in soil acidity (H+, Al3+) the clay
content of Ultisols gives them a nutrient retention capacity
greater than that of Oxisols, but less than Alfisols or
Mollisols. Ultisol soils can be agriculturally productive with
inputs of lime and fertilizers. Red Soils of the SE US
Oxisols
• 10 - Oxisols
• Oxisols are the most weathered of the 12 soil orders in the
USDA soil classification system. (See Lesson 2 -- Processes
of Weathering.) They are composed of the most highly
weathered tropical and subtropical soils, and are formed in
hot, humid climates that receive a lot of rainfall. Oxisols are
located primarily in equatorial regions.
• These soils are extensively leached, and the clay size
particles are dominated by oxides of iron and aluminum,
which are low in natural fertility (Ca2+, Mg2+, K+) and high in
soil acidity (H+, Al3+). While Oxisols are typically physically
stable, with low shrink-swell properties and good erosion
resistance, these soils require extensive inputs of lime and
fertilizers to be agriculturally productive
Tropical Rain Forest Soil
(humid, tropical climate)
What Am I?
Acidic
light-colored
humus
Iron and
aluminum
compounds
mixed with
clay
Fig. 3-24b, p. 69
Oxisols
Only found in U.S. in Hawaii
Forest litter leaf
mold
Humus-mineral
mixture
Light, grayishbrown, silt loam
Dark brown
firm clay
Deciduous Forest Soil
(humid, mild climate)
Fig. 3-24b, p. 69
alfisol
Coniferous Forest Soil
(humid, cold climate)
Acid litter
and humus
Light-colored
and acidic
Humus and
iron and
aluminum
compounds
Fig. 3-24b, p. 69
Spodosols
Mollisol
Profile
What
characteristics
make me
mollisol in the
pic?
Dark A Horizon full of organic matter.
Grass above, mollisols common in
grasslands.
•
•
•
•
Develop from volcanic material.
High water holding capability.
Fix phosphorus for plant use.
Productive forest in the Pacific NW have this
soil type.
andisols
Vertisols
• Come from parent
material that is rich in
clay, like lake beds or
shale bedrock.
• Swell and shrink in
response to water.
• Swell w/water
• Shrink w/o water; causing
engineering problems and
crack w/o water.
Vertisols
Histosols
• Parent material:
• incompletely decomposed plant remains, with or
without admixtures of sand, silt or clay.
Waterlogged areas (bog or peat soils)
• Environment:
• Histosols occur extensively in boreal, arctic and
subarctic regions. Elsewhere, they are confined to
poorly drained basins and depressions, swamp
and marshlands with shallow groundwater, and
highland areas with a high
precipitation/evapotranspiration ratio.
• From www.isirc.org
gelisols
• Frozen soils, where there is perma frost.
• Alaska in U.S.
Entisols
• http://www.cals.uidaho.edu/soilorders/entisols.h
tm
• Entisols are soils of recent origin. The central
concept is soils developed in unconsolidated
parent material with usually no genetic horizons
except an A horizon. All soils that do not fit into
one of the other 11 orders are Entisols. Thus,
they are characterized by great diversity, both in
environmental setting and land use.
• (little to no horizon development)
• Very Diverse: Saudia Arabia deserts, rivers valleys
around the world, mined areas.
Inceptisols
• inceptisols (from Latin inceptum, "beginning") are
soils that exhibit minimal horizon development.
They are more developed than Entisols, but still
lack the features that are characteristic of other
soil orders.
Both inceptisols and entisols have not fully
developed, they lack complete horizons, and have
formed from fairly new parent material, or areas
with low water/precipitation, thus the soil
develps slowly.
Lots of rock, not a lot of topsoil
Characterize its Soil Horizons!