Lithosphere notes

Soils as an ecosystem

• Everything integrated in soils (geology, water, organisms, air) to create an ecosystem consisting of organisms interacting eith their physical environment. (Think Lithosphere, Chemosphere, Atmosphere, Hydrosphere, and Biosphere all coming together to create a soil ecosystem).

• These interactions vary, creating unique soils and aboveground ecosystems supported by the soil below.

Name some important things about soil

• Soils support aboveground ecosystems and their wildlife

• Soils select for specific land-use and soil management influences nearby ecosystems

• Soil processes influence freshwater ecosystem health

• Soils support endemic and rare plant species

• Soils provide 95% of all of our food

• Soils are a finite resource —> can take about 1000 years to form 1 cm of soil

  • eroded by deforestation, industrialization, erosion and agriculture

  • can be protected

• Can be used for art

• Soils can benefit human health

What is soil?

• Simple: Soil is weathered parent material (e.g., rock) that is capable of supporting life

• Detailed: The unconsolidated material at the Earth’s surface consisting of minerals (sand, silt, and clay) and organic matter that serves as a:

  1. Habitat for organisms

  2. Medium for plant growth

  3. Recycler of nutrients

  4. Reservoir for water

  5. Modulator of the Earth’s atmosphere (can be a sink for carbon dioxide and methan etc.)

  6. Building material

What is soil made of ?

Approximately:

• About 50% solid

• About 50% pores

  • 25% air

  • 25% water

  • 45% Mineral Particles

  • 5% Organic matter

    • 80% Dead organic material

    • 10% Roots

    • 10% Organisms

What is the influence of past geologic events on the present landscape and soil?

The underlying rock and other deposits from past events determine:

• soil type

• topography

• water flow- surface and internal

• water storage and aquifers

• mineral deposits (parent material and its influence on the resulting soil)

• erosion and sedimentation

• vegetation

• habitats - human and animals

What are the four major geological events that shaped Québec?

1. Formation of the Grenville province

2. Formaion of the St. Lawrence Platform

3. Magma Intrustions

4. Glaciation

Explain the Formation of the Grenville province

• Subdivision of the Canadian Shield, where the oldest rocks in the region are found.

• Chain of mountains formed between 1500 and 900 million years ago.

• Laurentia collided with other continents dragged by tectonic plates.

• Himalaya-type mountain range grew out of this collision

What is left behind now of the Grenville Mountain Range?

• Small, old erorded mountains that have eroded over millions of years

• Left much smaller Laurentian mountain range

• Mnt. Tremblant and the hills in Oka example

• Oldest rocks of metamorphic origin (formed under high pressure or heat that occur during the collision of the landmasses) found in Québec are from this period

Explain the formation of the St. Lawrence Platform

• Near end of Precambrian, about 600 million years ago, hug continent began to break up

• During Paleozoic, rift formed in the Grenvillian mountain range and gradually widened into an ocean.

• From 600 to approximately 420 million years ago, Earth’s crust gradually subsided and marine sediments accumulated on continental shelf that formed a platform along the margins of the land.

• That ocean aka Lapetus, recieved enormous amounts of fossiliferous mud and sand, that gradually transformed into rocks important to economy (grey limestone —> Montreal Greystone)

• Montreal region at the time, near equator, over course of millions of years, Africa and North America move toward each other and form a new continent, collision creating the Applachians

• St. Lawrence Lowlands emerged from the ocean and erosion started again in the newly formed land.

• This bed of marine material now underlies most of the St. Lawrence Lowlands

  • Sedimentary rocks formed from the limestone beds easily eroded away

Which geologic events do we consider to be more “recent”?

• Magma intrusions

• Glaciation

The “recent” features that formed are from what type of events?

• Depositional and erosion events

• These events had destructive (breaks down) and creative (builds up) forces

• Erosion will move materials to other areas and create new possibilities or it will expose what lies underneath —ancient seas, old mountain ranges etc.

• Deposition: material deposited from geologic events

• These processes lay the foundation of the parent material: The unconsoldiated mineral or organic material from which the true soil develops

Explain the igneous intrusions through the limestone

• Magma rose from below the Earth’s crust

• Later, below the surface, the magma slowly cooled, crystallizing into Igneous rocks, intruding through the limsetone platform (stays inside, slower cooling than if there was an eruption, so denser crystallization and even more resistant to erosion)

• Igneous intrustions are more resistant to erosion than limestone

Why are igenous intrusions more resistant to erosion than limestone

• Limestone (calcium carbonate) surrounding igenous intrusions more easily weathered (physically and chemically decomposed)

• Igneous granite formed by slow cooling magma is very resistant

What is left behind in the landscpae from the igenous intrusions?

• The Monteregian Hills (Mount Royal, Mount St. Hilaire, Rougemont and others) remaining, uneroded igneous intrusions/magma conduits because the surounding sedimentary rock (limstone) has eroded away.

Explain the glaciation

• The glaciers were 2 to 3 km thick —> crust of Earth depressed

• Glaciers

  1. wore away and levelled the Grenvillian and Monteregian Mountains

  2. left behind a trail of stone and rocks and glacial till

  3. Created seas (Champlain Sea) and deposited clays

• Three ice sheets (Greenland Ice Sheet, Laurentide Ice Sheet, Cordilleran Ice Sheet)

• Barnes Ice cap in Nunavut, remnant of the Laurentide Ice Sheet —> estimated to melt in 300 years

• Glaciers pick up rock material as they move, rocks can be plucked up or fall on top of glacier as it moves.

• When glaciers melt or retreat this rock is left behind.

Aftermath: Glacial retreat and Isostatic rebound—> formation of seas and lowlands

1. During peak glaciation, the weight of the glacier caused the Earth’s crust to sink

2. This also pushed the mantle outward and up

3. During deglaciation the crust is still depressed and ocean water and glacier melt water cover the land.

4. Post-glaciation, once the ice is gone, the land starts to rebound (mantle flows back, not quick process, takes a very long time)

What is left behind after a glacier?

• Glacial till: accumulations of unsorted, unstratified mixtures of clay, silt, sand, gravel and boulders

  • Rigaud ‘potato’ fields

What did the aftermath of the glaciation lead to the formation of?

The Champlain Sea:

• After glaciers melted, the land lower from the weight of the ice allowed the Atlantic Ocean to move in, forming the Champlain Sea.

• With crust slowly rising, the sea water became trapped from entering the ocean.

Hudson Bay and northern lowlands and peatlands:

• Hudson Bay: a result of crust rebound. Ice sheet so heavy it depressed the earth’s crust. When ice melted slowly began to rebound —> rebound still occurring (1cm/ year or less)

What was left behind when the Champlain Sea retreated?

• When Sea retreated it left behind clay sediments 25 to 30 m thick

• Called Leda clay —> sensitive to distrubance

• Construction, earthquakes, or stream erosion can liquefy leda clay and cause spectacular earthflow landslides

Why are Leda Clays so unstable/sensitive?

• Structurally stable with saltwater: Salts in the seawater, holds the clays together

• Unstable after salts removed from freshwater inputs

Some consequences of the instability of Leda clay deposits

• Landslides after heavy rainfall

Geological Events: Monteregian Hills consequence of erosion or deposition?

Erosion (eroded the limestone around the intrusion)

Geological Events: Limestone beds consequence of erosion or deposition?

Deposition

Geological Events: Leda Clay consequence of erosion or deposition?

Deposition

Defintion of Erosion

• Destructive force: breaks down materials

• Moves materials oto other areas and create new possibities or it will expose what lies underneath — ancient seas, mountain ranges etc.

Definition of Deposition

• Creative force, it builds up

• Material left behind from geologic events

Deposition and Erosion lay the foundation for what?

Parent Material: The unconsolidated mineral or organic material from which the true soil develops

What are the bases for the resulting soils from the Glaciers and the Champlain Sea?

• Glacial till: mixture of assorted particles —> sand, boulders

• Alluvial sand deposits

• Marine sediments

Resulting soils from Glacial Till

• Soils contain little organic material, and are characterized by an abundance if surface stones and boulders

• Clay and sand mixture, typically have good drainage

Resulting soils formed from Sand Deposits

• Formed from sorting by the waves of the Champlain Sea, after the glaciers melted

• The finest particles (smallest and easiest to carry) were carried offshore and deposited as clay and the sands and gravels accumulated along the shorelines

  • Sands and gravels accumulated along the shorelines

• Soils that develops on these sands and gravels is ideal for fruit trees, and root vegetables, and certain pine species (because they like soil with good drainage)

Resulting soils fromed from Marine Deposits

• Clay deposits from the marine beds of the old Champlain Sea or deposition of materials (alluvium) carried away by running river water

• Resulted in a large ‘clay belt’ in Eastern Canada (beside the Leda clay)

  • Poor drainage hard to cultivate things

• 
  

Are rates of soil formation fast or slow?

Rates of Soil Formation Vary but are Consistently Low (< 1mm yr^-1 )

What is parent material?

• The starting point for soil development

• Unconsolidated rock and mineral fragments just below the soil

Important to note that parent material can be a result of multiple processes (Transported or in place)

Remeber called parent material because it is not always rock

Parent Material: In place

• Parent material is the same as underlying bedrock

• Develops locally thus not many things added

  • Bedrock (Residual)

  • Organic deposits (e.g. peat)

Parent Material: Transported

• Parent material is different from underlying bedrock

  • easy to tell based on:

  • colour

  • composition of the minerals

What are the different ways for parent material to be transported?

• Water Transport: (Alluvial, Fluvial, Lacustrine) Alluvium —> sorted

• Air Transport: (Aeolian/Eolian) Loess deposits fine clay and silt —> sorted

• Gravity Transport: (Colluvium) earthquakes and landslides common —> unsorted

• Ice Transport: (Moraine) Glacial Till —> unsorted

Important to note that parent material can be a result of multiple processes (Transported or in place)

Parent material to soil caused by what process?

Weathering

Soil formation is also called what and how is it defined?

• Soil genesis

• The process of creating soil from parent material through time

  • In our region of northeast Canada -500 years for 2.5 cm of soil —> colder temperatures usually means slower, think biochemical processes in most organisms is regulated by temperature

What are the five factors influencing soil formation?

CLORPT(H)

1. Cl =climate

2. O= organisms (including humans)

3. R= relief (topography)

4. P= parent material (properties of the parent material inform how the soil will be formed: which process/factor is the parent material more susceptible too?)

5. T= time

What determines rates of formation?

Soil is formed by pedogenic processes —

(transformations, translocations, additions and losses) acting on parent material.

Examples of additions

• Forests and organic matter, photosynthesis fixes a lot of CO₂

• Air flow of soil particles from one place to another

Examples of translocation

• Earthworm bowel movements as they go from A to B

• Another being that clay is transported from near the surface and is deposited lower in the soil profile because clay can be suspended in water

Examples of transformation

• Mottling: presence of spots, blotches, or streaks of different colours (such as gray, yellow, orange, or red) mixed with the dominant background colour of the soil. —> redox reactions

  • wet —> air cannot penetrate the soil

  • dry —> air can penetrate the soil

Examples of losses

• After wildfires —> roots not as stable to hold things together—> can lead to landslides

  • Post-fire, soil is unstable and can be transported with heavy rains

• Agricultural activities

Defintion of a regolith

A layer of unconsolidated materials overlaying the hard, un-weathered bedrock

Soil geological defintion vs traditional

Geological: Loose surface of the earth as distinguished from soild bedrock

Traditional: Soil is defined as the naturally occurring, unconsolidated (loose) mineral or organic materal at leas 10 cm think that occurs at the earth’s surface and is capable of supporting plant growth.

What is the definition of weathering?

Any of the chemical, biological or mechanical (physical processes) by which rocks exposed to the weathering undergo chemical decomposition and physical disintegration

What does the rate of weathering depend on?

Depends on temperature, moisture, organisms and the “strength” of the parent material.

Think about how higher temperature and moisture could lead to more active chemical process.

How/where does weathering “usually” start?

• “Usually” starts at the earth surface and moves downwards creating the soil profile —physically and chemically altering the original material

  • Note that a lot of the factors are usually from the top but something like organisms or even could also come from below, secreting acid for example, or also ground water or human activity like pipes buried under layes that could change the temperature and moisture for example.

What are the two main types of weathering?

1. Mechanical weathering: physical breakdown of rocks without changing the chemical composition

2. Chemical weathering: breakdown of minerals by chemical reactions with air (or oxidation), acids, or water

   • Water is the most widespread weathering agent (both mechanical and chemical)

The effectiveness of both physical and chemical weathering depends on the strength of the rocks and minerals

Examples of mechanical (physical) weathering

• Wind abrasion

• Freezing and thawing

Examples of chemical weathering

• Hydrolysis: hydrogen ion (H⁺ ) in water molecules react with rock minerals, weakening them.

  • Example: for the igneous rock granite, the mineral feldspar is hydrolyzed to clay secondary minerals, which are crumbly and weaker.

  • Although igneous rocks are stronger than others (i.e. limestone) it doesn’t mean they are imprevious to weathering

• FYI: During chemical weathering certain elements are released into solution and provide nutrients for organisms

• Dissolution: water has small amounts of carbonic acid that react with rock minerals (limestone) “pulling them” awar from the rocks and into solution (over years and years).

About organisms and weathering

• Organisms can do two weathering types

  • Example: Physical weathering from pressure of tree roots

    • Belowground, roots produce CO₂ and organic acids that acidify soil and promote chemical weathering

  • Example: Chemical weathering from acids produced by plants and microbes

    • Lichens on rocks produce organic acids to dissolve the rock and thus release nutrients for the plant’s growth

Climate and its effect on weathering

• Directly affects weathering through temperature and precipitation (moisture) which determine the rate and type of weathering

  • Warm, wet climates promote chemical weathering

  • Cold, semi-moist climates promote physical weathering (particulary frost weathering)

  • Dry climates give low rates of weathering (especially chemical weathering) (most chemical processes require water)

Climate indirectly affects weathering through the type of vegetation which can affect soil acidity and thus chemical weathering rates.

Soil horizons

Soil profile defintion

A vertical section of soil from the ground surface to the parent rock showing the different horizons or layers

What is in the upper and lower limits of a soil profile

• Upper limit: air, shallow water, live plants or loose plant material that has not begun to decompose

• Lower limit: the depth to which soil weathering has been effective (beyond which there is no alteration of the original parent material)

Name the soil horizons

• O Horizon —> organic layer (leaf litter)

• A Horizon —> Surface soil (topsoil)

• E Horizon —> Leaching layer (gives nutirents, eluviation)

• B Horizon —> Subsoil (recieves nutrients, illuviation)

• C Horizon —> Substratum (can contain groundwater)

• R Horizon —> Bed rock (parent material)

More on the O Horizon

• Characterized by degree of decomposition

• Develop from accumulation of leaves, twigs, moss, and woody materials

• They are normally associated with forested soils or places where litter inputs are high and decomposition rates are not fast

• This horizon not typically present in managed ecosystems

More on the A horizon

• Surface or topsoil

• Located near the surface

• First horizon formed after the O-layer

• A mix of organic material and minerals

• Where the highest concentrations of carbon, nutrients, and organisms (including plant roots) are located

• Can be a few cm to >100 cm deep

• Darker in colour due to all of the organic matter

• Dominant processes are additions and losses

  • Additions from organic matter

  • Losses from nurtient leaching

More on the E horizon

• Area of leaching or eluviation

• If present, located below A horizon

• If it is only partially developed, can be associated with the A horizon as “Ae”

• Zone of eluviation where dissolved clay, organic matter, iron and/or aluminum is carried downward.

• Most dominant in highly weathered older soils, acidic soils or wet climates

• Can be lighter in colour, grey, white —> because fo the leaching

• If present, usually much thinner than A and B horizons

More on the B horizon

• Subsoil

• Located below A horizon (or below E if present)

• Zone of accumulation (illuviation) of material from A horizon, especially clay

• Tends to have finer texture (more clay)

• Lower concentrations of organisms and carbon

• Can be exposed with erosion, construction

• Less weathered and dominant processes are transformations and additions

  • If you are accepting things you can be transfromed by them

  • No doubt accepting some things from above and thus additions

More on the C horizon

• Weathered parent material

• Minimally altered from parent material

• Represents the lower limit of the soil profile

Soils have different horizonization depending on their age, what can we do with that?

We can use these horizons to classify soil

• Baby soil —> Regosol

• Adolescent soil —> Brunisol

• Adult soil —> Chernozem

• Elderly soil —> Oxisol, not in Canada

What are the 10 identifiable soil orders in Canada that CLORPT produces

Based on the Canadian system of classification:

• Brunisol

• Chernozem

• Cryosol

• Gleysol

• Luvisol

• Organic

• Podzol

• Regosol

• Solonetz

• Vertisol

In purple is the most common

These soil orders are then subdivided into 5 more levels of classification into about 23 000 different soil series

What are the classification levels of soil (Soil taxonomy)

• Order

• Great Group

• Sub groups

• Families

• Series

What is identifying which order a soil belongs to is based on?

• Soil properties that can be objectively measured or observed such as:

  • Horizons, moisture, temperature, colour, texture, chemistry (pH, organic matter content, clay, depth…)

More on soil taxonomy

• All soils belong to one fo the 10 soil orders

• The order names often end in “sol(s)” or “solic”

• Soils within an order have one or more characteristics in common

  • Not perfect, soils in the same order are not identical, they can be very similar but also very different.

What soil lies beneath each landscape?

• Chernozem —> grassland

• Organic, Gleysol —> wetland

• Brunisol, Podsol, Luvisol —> Forestland

• Cryosol, Organic/Gleysol —> Peatland

Forest soil: Brunisols

• Least developed of the forested soils

• Begin from a Regosol and end up as a more ‘mature’ Podzol or Luvisol

• Drier and cold regions, northern ON, QC, southern Yukon

  • Annual precipitation around 700 mm, 0 degrees celsius to 6 or 7 degrees celsius

• Coniferous, Boreal forest. Often just below the permafrost zone.

What are the diagnostic features of Brunisols:

• Soil age is young — shallow soil depth due to little weathering of igneous sandy glacial or marine sediment and the dry cold conditions

• Can be acidic or alkaline depending on parent material

• Dominant process is physical weathering —> because it’s drier

• Often has good drainage

• Can have E horizon (if in place with more precipitation), with finer materials (e.g. Fe and Al) deposited in the B horizon (reddish brown colour)

• Key: B horizon is only moderately developed (Bm horizon where the m is for moderate)

Forest soil: Podzols

• Develop from same parent material as Brunisols but in areas with more precipitation. Sandy igneous parent material

  • Montreal 1000 mm per year remember

• Mixed foresrs — dominate confiers, mostly in cold and temperate climates

• Thus, more mature soils with a more developed B horizon

• Depth of sand varies from 0.5-1.5 m (think Champlain Sea and some sand deposits)

What are the diagnostic features of Podzols?

• Well to moderately drained soils

• Often acidic (low pH) because minerals from parent material are low in base cations (e.g. calcium), acidic plant inputs, and high organic matter

  • Have a lot of conifers and conifer needles are very acidic —> so acidic organic inputs

• Extreme weathering leads to well-defined pale E (Ae) horizon

• Podzolic B horizon — accumulation of organic matter combined with iron (Fe) and aluminum (Al)

• Red colour in the B horizon is the translocated oxidized iron accumulation

Forest soil: Luvisols

• Moderate and cool moist climates

• Loamy (mix of clay and silt) and clay soils from underlying sedimentary rocks and marine beds

• Good for agriculture because of fertility and pH

• Extensive throughout interior Canada (Ontario and onwards especially Alberta)

They are a cousin to Podzols

What are the diagnostic features of Luvisols?

Though they are cousins to Podzols the key difference is the pH and texture

• Key feature is textural contrast between the A and B horizon, where clay has accumulated

• Have an eluviated Ae (E) (less clay) and an illuvial textural B-translocated and deposition of silicate clay

• Parent material high in Ca and Mg (base cations) so soils tend to be neutral or alkaline pH values, especially in the B horizon

  • Can be neutral because organisms alwyas provide acid, so even if there is a lof of Ca or Mg in the soil the pH could be around 7 and so more neutral

Grassland soil: Chernozem

• Common in southern prairies and parts of interior B.C.

• Found in regions that are cool (soil temperature is cool O degrees Celsius to 6 degrees celsius), but are semiarid and sub-humid. Thus the vegetation is grassland or transitional grassland-forest (shrubs)

  • Far from ocean caused temperature regulation

• This soil order is not found in Eastern Canada. Also present in U.S. and Eastern Europe grasslands (steppe)

Water is major factor in vegetation (far more so than temperature)

Diagnostic features of Chernozem?

“chernyi” (black) and zemlya (soil)

there will be a deep root system cause drier

• High organic C (2-17%), very fertile! Dark and thick (>10 cm) A horizon, neutral pH (result of parent material and organic matter)

• Well to imperfectly drained soils, with strong aggregate structure that does not break down when wet

• High organic matter helps bring salts into solution which then move down to B horizon. High base (dominant calcium) saturation in the B and C horizons from the movement of dissolved salts from the A horizon deposited in the B or C horizon.

Even though forests have more biomass than grasslands they have less organic matter because forests are more moist and more active and conducive to activity and can better use the organic matter than in grassland.

Carbon released in organic matter is food for soil organisms —> which then churn and among other things provide nutrients to plants.

What has agriculture changed in Canadian Prairie Chernozem?

15 to 30% of the original soil carbon was lost after conversion of the native Praire to agriculture

• When we till is, we rotate the subsurface soil to surface and you expose it and speed up decomposition rate —> useful for farmers but that organic carbon when released becomes carbon dioxide

Wet soil: Gleysols

• Found in wetlands and some forests in Eastern Ontario and Quebec (St. Lawerence Lowlands)

• Can be formed from the marine deposits of the old Champlain sea beds (think of the clay belt)

• The drainage is poor due to the clay layers. Thus soils are usually saturated with water

• Overlying vegetation must be able to tolerate flooded conditions

• High organic surface layers can accumulate under saturated conditions and low decomposition rates (aerobic conditions because of high water saturation).

Diagnostic features of Gleysols

• Soils are saturated with water and under reducing conditions during some part or all of the year unless they are artificially drained— even after draining they would still be classed as gleysol

• Acidic to neutral near surface, high pH (alkaline) in subsurface

• Key feature is gleying features (“mottling”): red and blue colours from changes in oxygen content (reducing condtitions)

Explain Gleying/Mottling in Gleysol

• Gleying is the process of waterlogging —> lack of oxygen —> reduced conditions

• A mostly grey or bluecolour indicates long-term reduced (anaerobic) conditions where iron is mostly Fe²⁺

• Orange/red mottling appears when the soil becomes exposed to oxygen again — oxidizing iron back to Fe³⁺

Remember that oxidized means lose and electron and reduced means gain an electron

Cold soil: Cryosols

• Occupy much of the northern third of Canada (cover 35% of Canada)

• They form in regions that have a mean annual soil temp <0 degrees C

• Soils that have permafrost within 1 m of the surface —> always frozen

• Long, cold winters and short, cool summers

• Primary productivity is low but decomposition is also low

Diagnostic features of Cryosols:

• Can be organic or mineral based

• Horizons can include: active layer, a zone of cryoturbation, and permafrost zone

• Cryoturbation is frost action causing patterned ground features and discontinuous horizons

• Cryosols with an ‘active’ layer (freezes and thaws) can have other soil orders on top (Gleysols and Organic)

  • freeze and thaw very uneven/unequal because of uneven UV radiation sun exposure etc.

• Suffixes y (evidence of cryoturbation) and z (permafrost)

Important layers:

• Active Layer

• Transitional/ cryoturbation layer

• Permafrost layer

Wet/cold soil: Organic Soil (histosol, peats, bogs, fens, mucks)

• They contain more than 17% more organic C (about 30% or more organic matter) by weight

• Dominant in wetlands (Hudson Bay — largest wetland worldwide)

• Also found in depression areas where water accumulates

Diagnostic features of Organic Soils

• Minimum 40 cm in depth of peat. If <50 cm often classified as the ‘peaty’ phase of a Gleysol

• Require water-saturated conditions to accumulate

• If permafrost occurs at a depth less than 1 m from the organic soil surface, the soils are classified into the Cryosolic Order

• Saturated conditions lower decomposition rates and horizons accumulate overtime with new plant inputs

Describe the horizons of Organic soils

• O horizons and organic soils profiles characterized by a degree of decomposition (L, F and H horizons) —> from least to most increasing age and decomposition

• Process of deposition and accumulation of leaves, twigs and woody materials and/or mosses.

Cheat sheet for Soils found under forested and grassland systems, wetlands and Arctic

Describe the less common soils orders in Canada

• Vertisols: High clay content (shrinking and swelling clays), grasslands

• Solonetz: western Canada in arid regions. High salt content in upper horizons; grasslands

• Regosols: young, poorly developed

More on Grassland Soil Vertisols

• Soils with a high content (>60%) of smectite clay minerals, known as swelling clays. Formed from clayey glacio-lacustrine parent materials.

• Pronounced cracking as soils dry combined wuth surface soil falling into crack mixes soil to about 1 m depth

  • can even be massive and deep fissures in the soil

Grassland soil: Solonetz

• These soils have a high amount of sodium (Na⁺ ) and are considered “salty”

• Central Canada, semi-arid conditiins (including Australia)

• High Na arises from:

  1. marine deposits high in Na⁺

  2. May also occur from impeded “flushing” of soil with water movement that would otherwise help to prevent salt accumulation

• Negative impacts on farming

Regosols

• Poorly developed soils

• No B horizon (only an A and C horizon)

• In areas of extreme climatic conditoons — low to moderate vegetation growth and where rates of weathering are low

• Also occur in unstable environments (high erosion, hill slopes) that limit profile development

Important soil orders not in Canada — tropical soils (acidic and low fertility)

Utisol and Oxisols —> Both have:

• Purple, red, orange, yellow

• high clay

• high in iron aluminum oxides and manganese

• very weathered

Utisol vs Oxisol

• Utisol has distinct clay layers, subsurface zone of clay accumulation while Oxisol has no clay layers

Physical Properties: Impacts on the Soil Environment

• Porosity

• Erosion

• Water inflitration

• Water holding capacity

• Access

• Movement of materials and energy (wind and water is an example, carries energy from higher place to lower place)

• Organic matter content

• Nutrient availability

Definition of soil texture

• The proportion of particles of sand, silt, and clay in soil, expressed as a percentage based on dry weight of soil

More on soil texture

• Soil particles (i.e. sand, silt and clay) are distinguished by size

• Particles larger than 2 mm are not considered part of soil texture

  • Their influence on soil properties (nutrient retention) is considered to be minimal

• Only primary (sand and some silt) and seconday mineral <2mm make up soil texture (does not include soil organic matter)

• Size ranges reflect how soil particles behave and the physical characteristics they give to soils

  • Also dictate how we use the land

• Use a soil texture period to determine texture classes, with sand, silt and clay percentages —> together all three will equal 100%

  • Apex for clay 100%

  • Apex for sand 100%

  • Apex for silt 100%

Sand: Soil particles between 2.0 mm and 0.05 mm

• Can see with unaided eye

• Feels gritty between the fingers

• Usually consists of quartz, or other primary minerals

• Low surface charge/inert

• Low in nutrients

• Large particle size translates into rapid water drainage and presence of air between soil particles

Silt: soil particles between 0.05 mm and 0.002 mm

• Not always visible to unaided eye

• Feels smooth or silky (not sticky) between fingers when wet and powdery like flour when dry

• More weathered micro-sand particles made of quartz or other primary minerals

• Its smaller size means slower drainage and greater water retention —> gaps between particles are smaller

• Some surface charge (reactivity)

• Easily transported in water and deposited at river mouths (think of silt erosion and deposition, new land called chars in northern Bay of Bengal)

Clay: Soil particles less than 0.002 mm

• Shaped like tiny flakes or flat platelets

  • One particle is made up of several stacked plates

• Fine clays have 10 000 times the surface area as the same weight of sand (high specific surface area)

  • Ions inside close to the surface, charge can be revealed

• Composed of secondary minerals from the weathering of primary minerals and then recrystallization

• High surface charger (usually negative)

• Extremely small size means that air and water movement is very slow

Can you alter soil texture?

No!

• Management practices generally cannot alter soil texture in place

  • They have been formed over many, many years

  • You can alter soil structure but not soil texture

• It is best to find naturally occurring soil that meets one’s needs instead of attempting to alter the textural class.