What is meant by diagnostic horizon?
Compare CSSC (all soils in Canada) and USDA (soils on Earth) soil classification systems, to what extent they parallell each others + differ?
Pedon
The smallest unit that displays the full
range of properties characteristic of the soil type (scale of 1 to 10 sq.m)
–>”species”
Polypedon
group of similar pedons, collection of same soils (comparable to cluster of plants of same species
–>” community”
Soil series
class of soils, all with same diagnostic properties
Canadian System of Soil Classification (CSSC) horizons
Organic horizon: L, F, H (litter derived) or O (peats - wetland derived)
–> Different broken down levels: Litter, fermentation humus (=L,F,H)
Mineral horizons (<17% org. C (~<30% o.m. by mass)): A, B, C
–> diagnostic mineral soils
R – rock (too hard to dig with spade when moist)
–> included in soil profile in Canada
W – water or segregated ice layer in Cryosol
USDA soil hierarchical organisation
Series (1900), family (8000), subgroup (2500), great group(300), suborder (60), order (12)
CSSC soil hierarchical organisation
Series, family, subgroup, great group, order (10)
USDA diagnostic subsurface horizons
18 organised around origin, but distinguished by objective criteria
A. minimal accumulation (2)
B. accumulation (13)=
-silicate clays (4) - clay minerals
-organic matter (3)
-inorganic salts (5)
-sulfur (1)
C. pan development (3); hardening in soil profile
USDA diagnostic surface horizons (epipedons or A horizons)
Criteria: organic matter content, thickness,
colour, calcium & magnesium content
- Melanic: derived from volcanic materials
- Mollic: high base saturation
- Umbric: low base saturation
- Histic: formed in organic matter
**not core one: 5. Anthropic: man-made soils (mining)
- Ochric (thin + pale): low base saturation
-used as “default” category
Soil classification/taxonomy/pedology is based on
- objectively observed or measured soil
properties defining the diagnostic horizons (facts, can be assessed exactly)
–>Criteria: colour-Munsell colour chart, texture, o.m., moisture status, temperature, % base saturation, clay content, Fe & Al oxides, pH, clay activity - Unique nomenclature (e.g. American)
–>Classification depends on purpose, and population (Canada vs US vs Russia)
–>Different soil taxonomies use similar criteria but different terminology (nomenclature, naming conventions)
Hierarchical organization of soils, based on …
genesis (criteria that indicate the soils developmental history, to what extent soil is developed)
–>climatic genesis (soil temperature + dry/moist/wet)
–> Histosols + Organics are determined by local anaerobic conditions (not by climatic conditions)
Characteristic combinations of
(2)
give you the unique elements of the classification. So, the whole system depends on how you define …
Diagnostic surface horizon over
Diagnostic Subsurface horizon/s
+ sequence of soils
your diagnostic horizons
USDA Nomenclature
Logical, compact and informative; but foreign
–>Names strung together using root of full name. Root = soil order
–>Names grow to left – refined or specified by adding “adjectives” to root
Root is soil order (one of 12),
–>modified by prefix (qualifiers) to create Suborders (+1)
–>Many types of qualifiers, see Tables of formative elements for suborder and great groups (+2), subgroups (+3), family (+4), series (+5)
-Soil moisture regime soil formed under (aquic, udic, ustic, aridic, xeric)
-Soil temperature regime soil formed under (cryic, frigid, mesic, thermic)
- Entisols; (ent)
New soils (slightest weathering)
little/no horizon development
–> no B horizon, not enough soil development
–> little variance between C horizons
–> A horizon onto subsurface materials
Erosion
Aridity
Varied locations, all continents
–>CSSC = regolic
- Inceptisol (ept)
Mild weathering
various conditions
Young soils
No mature horizons, some diagnostic features
Weakly developed A (usually ochric)
Varied locations, all continents, poles»
–>CSSC = Brunisolic (brown soils)
- Andisols (and)
**special parent material
Mild weathering on volcanic ejecta
Volcanic ash soils
Melanic A with high o.m. content
light, easily worked (plowed/tilled), little aggregations
Erodible in arid conditions
Coast of Americas
–>CSSC = not distinguisd
- Gelisols (el)
Defined by climate
Slight weathering
Very cold, permafrost
Frozen soils
Little development because of low temperature
Permafrost (frozen for over 2 years, unlikely to thaw every year) within top 100 cm of soil profile
Typical frost churning = road damage, permafrost landscape
–> Ice wedges; highly wet materials frozen into wedge
Nothern hemisphere, Alaska, high in mountains, alpine areas, poles»
–> CSSC= Cryosolic
- Histosols (ist)
Organic soils without permafrost
wetland soils
little profile development due to anaerobic conditions
–> no O2 = o.m. break down is stopped so it builds up
Deep accumulation of organic matter (thick layers-substantial depth of o.m., not just litter on top)
–>Dark to black/grey/brown
–>Very low density
–>high water-holding capacity
Weak; easily cultivated, easy to separate materials
Wet conditions
–>water = only limitation in that profile
Decomposes when aerated (worked or drained)
–> cultivating or draining soil = profile dries up (pores = air so o.m. breaks down), soil lowers down
High latitudes»
Everywhere wetlands (water saturation in profile that sits and prevents o.m. break down)
–> CSSC= Organic, then subdivided with extent of o.m. break down:(Fibrisols (Of), Mesisols (Om), Humisols (Oh))
–> significant area of Canadian peatlands
- Aridisols (id)
Desert shrubs
Grasses, dry
largest global order, largest landmasses
>90 days soil moisture insufficiency (long dry period in year)
Light coloured (ochric) A horizon; not thick or dark enough
Unleached B horizon; too arid, not enough water to wash anything away = nutrient-rich BUT not productive (because no water)
Accumulation of carbonates, gypsum, soluble salts, exchangeable sodiums (= problematic)
Low soil development, lots of rocks
–> stone pavement = indicator of aridisols
–>petrocalcic horizon (harden layer, cemented with calcium carbonate)
soil of deserts, not widespread, most subtropical areas
–> CSSC = no equivalent, not important enough here
–> Canadian dry prairies; wind erosion risk, salt risk
- Vertisols (ert)
*Soil (Swelling clays) = special feature
* High base status
* High activity clays
* Dry season
* Limited global distribution: drier, warmer climates & base rich parent materials (leached away, remain in soil), seasonal drought-well defined dry season
- Strongly active clays, >30%, to 1 m depth
- Dark colour, not necessarily derived from o.m.
- Remarkable, notable features (cracks, gilgai, slickensides, self mulching)
- Difficult to work/cultivate (sticky when wet (heavy, minerals stick together), strong when dry = rock)
–>because of swell/shrink
–> but highly fertile due to high clay content (base saturation)
–> CSSC = Vertisolic (>60% clay, at least half is smectite}
–> Localised distribution in Canada, must be identified because problematic = southern prairies, BC interior
–>* CSSC - argillopedoturbation
- Mollisols (oll) **most important?
Soft, dark
* Accumulation of calcium-rich o.m. to form thick (>10 cm deep), dark, mollic / chernozemic
–> not highly leached environment
A-horizon, with high base exchange
capacity
* Breaks up in crumb structure but soft
* Cool, sub-arid to sub-humid plains of prairies
* Economically important; agriculture (productivity)
–> grassland soils in prairies
–> russia, ukraine
- Semi-arid to moist
–> little rain can cause calcium carbonates to accumulate at bottom of profile) - Grasslands, mollic epipedon (mollic = soft –> easily plowed)
–> CSSC = Chernozemic (Black Earth), some
Solonetzic soils
–> typical prairie landscape
–> climatic gradation???
- Alfisols (alf)
Mildly acid clays
Moist, mildy acid
Clay accumulation
- More weathered than mollisols, less so than
spodosols (podzols) - Typically soils of deciduous forest or
savanna, all continents - Defined by accumulation of clays: >35%
base saturated (= mod. leaching) - Argillic, maybe natric or kandic
- Typically have thin ochric A, & may have E
–> CSSC = Luvisolic, some Solonetzic
- Spodosols (od)
Spodic horizon
Cool, wet, sandy
Acid coniferous forest
Allow bases
Nothern hemisphere
- Intensive acid leaching, with spodic B (o.m. & Al (+Fe) accumulation)
–> Bh, Bs - Spodosol usually underlies light, eluvial albic horizon
- Coarse parent material, moist to wet climate
- Acid vegt: forest (particularly conifer) or heath
- Naturally infertile, but productive when fertilized
- Risk of leaching of nutrients (fertilizers)
- Risk of acid drainage
- Extensive distribution in Canada (forests, E & W)
–> CSSC = Podzolic
