Transcript SOILS PART III 2008.ppt

Canadian System of Soil Classification
Canadian soil scientists classify soils based on pedogenic processes in
cool climatic environments.
Ten Soil Orders
Differentiated on the basis of characteristics of the soils that reflect the
nature of the total soil environment and the effects of the dominant soil
forming processes
Brunisol
Chernozem
Cryosol
Gleysol
Luvisol
Organic
Podzol
Regosol
Solonetz
Vertisol
Great Groups
Classified on the basis of profile characteristics which have resulted
from soil formation.
Brunisolic Order
Melanic Brunisol
Eutric Brunisol
Sombric Brunisol
Dystric Brunisol
Chernozemic Order
Brown
Dark Brown
Black
Dark Gray
Cryosolic Order
Turbic Cryosol
Static Cryosol
Organic Cryosol
Gleysolic Order
Humic Gleysol
Gleysol
Luvic Gleysol
Online Resources:
http://sis.agr.gc.ca/cansis/glossary/
http://www.ucalgary.ca/geog/Virtual/SoilOrders/soilorders.html#anchor394443
http://www.physicalgeography.net/fundamentals/10v.html
Luvisolic Order
Gray Brown Luvisol
Gray Luvisol
Regosolic Order
Regosol
Humic Regosol
Organic Order
Fibrisol
Mesisol
Humisol
Folisol
Solonetzic Order
Solonetz
Solodized Solonetz
Solod
Vertic Solonetz
Podzolic Order
Humic Podzol
Ferro-Humic Podzol
Humo-Ferric Podzol
Vertisolic Order
Vertisol
Humic Vertisol
Subgroups
Sub groups are based on (i) how strongly the soil profile is developed as
a result of slope position and the amount of moisture that penetrates the
profile or (ii) how it represents a transition toward another soil order
Orthic
Eluviated
Duric
Gleyed
Rego
Calcareous
Solonetzic
Brunisolic
Luvisolic
Gleysolic
Histic
Fibric
Mesic
Humic
Terric
Ferra
Vertic
Regosolic
Limnic
Cumulic
Hydric
Lignic
Placic
Alkaline
Glacic
Fragic
Family
Classified on the basis of the parent geologic material characteristics
such as texture, mineralogy, depth, and/or reaction and on differences
in soil climatic factors (generally not used)
Series
Groupings of pedons with similar arrangements of horizons whose
color, texture, structure, consistence, thickness, reaction, and
composition fall within relatively narrow and well defined ranges.
Often named after places
Brunisol
Soils whose horizons are
developed sufficiently to exclude
the soils from the Regosolic order,
but that lack the degrees or kinds
of horizon development specified
for soils of other orders.
Occur under a wide variety of
climatic and vegetative
conditions. All have brownish
Bm or Btj horizons. The four
Great Groups - Melanic Brunisol,
Eutric Brunisol, Sombric
Brunisol, and Dystric Brunisol are separated mainly on basis of
thickness of Ah horizons and pH.
Chernozem
Soils that have developed under
xerophytic or mesophytic grasses
and forbs, or under grasslandforest transition vegetation, in cool
to cold, subarid to subhumid
climates.
These soils have a dark-colored
surface (Ah, Ahe, Ap) horizon and
a B or C horizon or both, of high
base saturation. The order consists
of the Brown, Dark Brown, Black,
and Dark Gray Great Groups.
Cryosols - High latitude soils, common in the tundra. These soils
have a layer of permafrost within two metres of the soil surface. The
image here is of a soil in a tundra landscape dominated by moss and
lichen vegetation. The soil profile has a permanently frozen ice wedge
beneath its surface.
Ice-wedge polygons
Sorted nets and circles
Stripes
Gleysol - is a soil found in an
ecosystem that is frequently
flooded or permanently
waterlogged. Its soil horizons
show the chemical signs of
oxidation and reduction.
Soils developed under wet
conditions and permanent or
periodic reduction. These soils
have low chromas, or prominent
mottling, or both, in some
horizons. The Gleysol, Humic
Gleysol, and Luvic Gleysol are
the three Great Groups.
Luvisol - is another type of soil
that develops under forested
conditions. This soil, however,
has a calcareous parent material
which results in a high pH and
strong eluviation of clay from the
A horizon. More developed than
Brunisols.
Eluvial (Ae) horizons and illuvial
(Bt) horizons present, with silicate
clay accumulation.
Develop under deciduous or mixed
forest or forest-grassland transition
in a moderate to cool climate. The
order is divided into the Gray
Luvisol and the Gray Brown
Luvisol Great Groups.
Organic - Soil composed of
organic matter in various
stages of decomposition.
Organic soils are common in
fens and bogs. The profiles of
these soils have an absence of
mineral soil particles.
The majority of organic soils
are saturated for most of the
year (exception = folisols).
They contain more than 17%
organic carbon and mineral
components are often absent.
The four Great Groups are
the Fibrisol, Mesisol,
Humisol, and Folisol.
Podzolic
Soils of coniferous forests having a
strongly eluviated zone beneath the
A horizon and podzolic B horizons
(Bh, Bhf, or Bf) in which
combinations of amorphous Al, Fe,
and organic matter have
accumulated. Acidic soils.
Three Great Groups are Humic
Podzol, Ferro-Humic Podzol, and
Humo-Ferric Podzol.
Regosolic
Insufficient A or B horizon
development to meet the
requirements of other orders.
The order is divided into the
Regosol and the Humic Regosol
Great Groups.
Solonetzic
Develop under grassland or grass-forest vegetative cover in semiarid to
subhumid climates. Stained, brownish solonetzic B (Bn or Bnt) and
saline C horizon. The surface may be an Ap, Ah, Ahe, and/or Ae
horizon. The order includes the Solonetz, Solodized Solonetz, and
Solod Great Groups.
Vertisolic
Clay soils that lack the degree of
development necessary for other Orders
and that have deep, wide cracks at some
time during the year and have high bulk
density.
These soils have marked shrink-swell
tendencies with changes in soil water
content resulting in wedge-shaped
aggregates and/or evidence of severe
disruption of horizons in the solum.
Simplified Key to Mineral Soil Orders
1. Is the Bf, Bhf, or Bh at least 10 cm thick? If this is true, then the soil belongs to
Podzolic Order. If false, go to the next step.
2. Is the Bg or Cg within 50 cm of surface? If this is true, then the soil belongs to
Gleysolic Order. If false, go to the next step.
3. Is Bn or Bnt horizon present? If this is true, then the soil belongs to
Solonetzic Order. If false, go to the next step.
4. Is Chernozemic Ah or Ap present? If this is true, then the soil belongs to
Chernozemic Order. If false, go to the next step.
5. Is Bt horizon present?If this is true, then the soil belongs to Luvisolic Order. If
false, go to the next step.
6. Is the Bm at least 5 cm thick? If this is true, then the soil belongs to Brunisolic
Order. If false, go to the next step.
7. As all the other possibilities have been eliminated, this soil belongs to the
Regosolic Order
The Soil Pedon
and
Polypedon
Diagnostic Surface Horizons
• Based on a unit called the epipedon.
• Usually located in the upper-most part of the
soil horizon.
• May also include properties of the eluvial
horizons.
1. Mollic Epipedon
•Dark surface colour due to organic matter
accumulation (>0.6% organic carbon throughout)
•>25 cm thick
•Relatively soft when dry due to organic matter
•Moistened at least 3 months of the year
•Found in grassland regions of the world
2. Umbric Epipedon
•Similar overall characteristics as the mollic
epipedon, except:
•Base saturation is lower than 50%.
Negatively charged sites that are attractive to non acid
(base) cations (Ca+, Mg+, K+).
•Develops in areas with higher rainfall or where
parent material has less calcium and magnesium
•A horizon may be darker
3. Ochric Epipedon
•Defined by what it lacks!
•Mineral horizon that is too light to be a mollic or
umbric epipedon
•Lower organic matter content
•Thinner than mollic or umbric epipedon (<25 cm).
•May be hard and massive when dry due to lack of
organic material
4. Melanic Epipedon
•Mineral horizon is very dark due to high organic
matter content.
•Organic carbon > 6%.
•Often found in areas of volcanic ash.
•Greater than 30 cm thick.
•Extremely light weight soil due to organic material
5. Histic Epipedon
•20 to 60 cm thick layer of organic peat or muck
•Organic matter content should exceed 35%
•Brown to black in colour
•Very low density
Diagnostic Subsurface
Horizons
• Many more than the 5 major surface horizons.
• Table 3.1 gives the complete list.
• Diagnostic subsurface horizons help us correctly
place a soil within the specific class.
1. Argillic Horizon
• Subsurface characterized by the accumulation of
clays (illuviation)
• Can be formed in place of translocated from the
upper horizons
• Clays often coat pore walls and ped edges
• Argillans or clay skins
2. Natric Horizon
• Possesses a similar silicate clay accumulation
• This is accompanied by at least 15% exchangeable
sodium
• Usually has a columnar or prismatic structure
• Found in arid or semi-arid environments
3. Kandric Horizon
• Contains an accumulation of iron or aluminium
oxides
• Generally low base activity in the clays.
– Kaolinite clay.
• Low cation exchange capacity = lower fertility.
4. Oxic Horizon
• Generally highly weathered.
• Very high in Al and Fe oxides (more than kandic
horizon)
• Low cation exchange capacity
• Horizon is at least 30 cm deep.
• <10% weatherable minerals in the fine fraction.
5. Spodic Horizon
• Illuvial horizon characterized by the accumulation
of colloidal organic matter.
– Organic matter that is in suspension and can’t be
separated out.
• Accumulation of aluminium oxides
• Characteristic of highly-leached forest soils
• Sandy parent material
6. Sombric Horizon
• Illuvial horizon, dark in colour because of high
OM content.
• Low degree of base saturation.
• Found in cool, moist regions
– Especially mountains in tropical or sub-tropical
regions.
7. Albic Horizon
•
•
•
•
Light coloured horizons.
Have been eluviated.
Low in clay content and Fe and Al oxides.
Usually found above spodic horizons.
8. Others
• Calcic, Salic, Gypric
– All contain accumulations of soluble minerals.
• Some subsurface horizons can form cemented or
densely packed layers called pans.
– Duripans and Fragipans.
• Can cause erosion problems.
Duripans and Fragipans
• Duripans
– Si-cemented clays, organic matter, CaCO3
– Arid, semi-arid climates.
• Fragipans
– High bulk density, brittle (very compact – not
the result of clay)
– More humid climates.
• Placic horizons
– thin layer cemented with Fe/Mn/O.M.
Soil Moisture Regimes
• Aquic
– Soils saturated with water
– Virtually no O2
– Evidence of poor aeration (gleying or mottling)
• Udic
– Soil moisture sufficiently high year round
– Humid Climates
• Ustic
– Intermediate between Udic and Aridic
– Some plant available moisture during the
growing season
– Significant periods of drought
• Aridic
– Soil is dry for at least half of the growing
season
– Moist for fewer than 90 days
• Xeric
–
–
–
–
Mediteranian-type climates
Cool moist winters
Dry summers
Long summer drought periods
USDA Soil Classification System
Oxisols, aridsols,
mollisols, alfisols,
ultisols, spodsols,
entisols,
inceptisols,
vertisols, histosols,
and andisols.
Aridisols
•soils that develop in very dry
environments.
•poor and shallow soil horizon
development
•light colored because of
limited humus additions from
vegetation (ochric epipedon)
Aridisols
•Second largest global coverage (12%)
•Characteristic water deficiency
•May have concentrations of soluble minerals (salt, gypsum,
calcium carbonate), due to lack of moisture
•Salinization in prone areas
•Distribution and use.
–Only moist for short periods of time each year.
–Generally not terribly productive without irrigation.
Mollisols
•grassland environments
•most converted into agricultural fields for crop growth
•dark colored surface horizon
•base rich
•quite fertile
The dark color of the A horizon is the result of humus
enrichment from the decomposition of litterfall.
Mollisols found in more arid environments often exhibit
calcification.
Alfisols
•form under forest vegetation
where the parent material has
undergone significant
weathering.
•illuviation of clay into the B
horizon
•moderate to high concentrations
of base cations
•light colored surface horizons.
•Parts of Louisiana to northern
Minnesota.
Oxisols
•tropical and subtropical latitudes
•high precipitation and
temperature
•quartz, kaolin clay, iron and
aluminum oxides, and organic
matter
•nearly featureless soil profile
without clearly marked horizons
Most highly weathered soils
Low available bases.
Can be worked when dry.
Fe and Al oxides found in these soils results from
strong chemical weathering and heavy leaching
Distribution and use:
8% of world soil areas
Not glaciated or eroded.
Best left as is, under forested environments.
Rapid nutrient cycling into trees.
Ultisols
•translocated silicate clay
•dominance of iron and aluminum
oxides
•iron oxides cause the A horizon of these
soils to be stained red
•Leaching causes these soils to have low
quantities of base cations
•Common in SE United States and
China (winter cyclonic storms and
Summer convection produce rains)
Formed on “old” land surfaces, usually under forested
conditions
• Have and ochric or umbric epipedon.
• Relatively acidic B-horizons
– Low base saturation of clays.
• Distribution and use.
– 9% of land surface area.
– Not great for agriculture in native state.
– Respond well to management
– Require fertilizer and lime.
Spodosols
•develop under coniferous vegetation in
cool, humid regions, and as a result are
modified by podzolization: acidic
•parent materials of these soils tend to be
rich in sand.
The A horizon of these soils normally has
an eluvial layer that has the color of more
or less quartz sand.
Most spodosols have little silicate clay
and only small quantities of humus in
their A horizon.
Mixtures of organic matter and
aluminium, with or without iron,
accumulate in the B horizon.
Entisols are immature soils that lack the vertical
development of horizons. These soils are often associated
with recently deposited sediments from wind, water, or ice
erosion. Given more time, these soils will develop into
another soil type.
Inceptisols are young soils that are more developed
than entisols. These soils are found in arctic tundra
environments, glacial deposits, and relatively recent
deposits of stream alluvium. Common characteristics of
recognition include immature development of eluviation in
the A horizon and illuviation in the B horizon, and evidence
of the beginning of weathering processes on parent material
sediments.
Vertisols are heavy clay soils that show significant
expansion and contraction with increases and decreases in
moisture content. Vertisols are common in areas that have
shale parent material and heavy precipitation (eg. cottongrowing region of Texas). Inverted profile due to cracks.
Histosols
•organic soils that form in areas of poor
drainage
•profile consists of thick accumulations
of organic matter at various stages of
decomposition.
Andisols
Develop from volcanic soil
Naturally-fertile
Though often located in zones of
rapid weathering, insufficient time often
has passed for soils to become highly
weathered
Melanic epipedons common
accumulation of oxides of iron and
aluminium as well as allophane
Rapid accumulation of organic matter
due to development of clay complexes
• Unique set of parent material conditions.
• Limited distribution.
• Distribution and use:
– Less than 1% of the land area.
– Generally very productive soils.
Gelisols
•perennially frozen soils of the Arctic and Antarctic regions
•extremely high elevations in the lower latitudes
•Fragile, easily eroded soils