Introduction to Soil and Soil Resources 2001

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Introduction to Soil and Soil Resources2001

• Lecture 2

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Tonight

• Review lecture 1
• Update on lab manual
• Soil Formation
• Climate -Vegetation - Soil Patterns
• Assignment 1

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Lecture 1 Review

• What is Soil?
• Texture, Structure and Colour

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Why is Soil Important?

• Agriculture
• Engineering
• Home for flora and fauna
• Life Support

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What is Soil?

• Three phase system
• Solid
• Water
• Gas

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What is Soil?

• Combination of
• mineral material
• organic matter
• pore space

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Soil Horizons

• Mineral and Organic
• Distinct layers of soil
• Approximately parallel to the surface
• Master horizons A B C O L F H
• Used to classify the soil

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Pedosphere

• Intersection of four spheres
• Hydrosphere
• Lithosphere
• Biosphere
• Atmosphere

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What is the Pedosphere?

• The envelope of the Earth where
• soils occur
• soil forming processes are active

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Soil texture

• Percentage of sand, silt and clay
• Size ranges of sand, silt and clay
• Hand and laboratory methods
• Texture triangle
• Example Clay Loam

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Soil Texture

• Affects aeration
• Affects water holding capacity
• Affects pore space

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Soil Texture

• Percent clay very important
• Swelling and non swelling clays
• Clay has a high surface area
• Cation exchange capacity

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Soil Structure

• Physical property
• Combination of primary soil particles into
  secondary particles, units or peds
• Different shapes and sizes

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Soil Structure

• Grade, size, shape of the arrangements
• Example Strong, coarse, angular blocky
• Structure affects the size and shape of pores
• Aggregation very important

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Soil Colour

• Tells us something about
• the air and water regimes in the soil
• the amount of organic matter
• the types of minerals that make up the soil

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Soil Colour

• Munsell Soil Colour Books
• numeric and qualitative
• hue
• value
• chroma
• E.g. Grayish brown (10YR 5/2 m)

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Bulk density

• Bulk density is
• Db mass of oven dry soil
• volume of soil
• Unit is g cm-3 or Mg m -3
• example on page 61 of text book

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Clarification of bulk density

• Slide 53 of lecture 1 may be
• confusing.
• Use slide 74 of lecture 1
• and slide 17 of lecture 2 for
• a clearer definition
• of bulk density.

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Particle density

• Particle density is
• Dp mass of soil particle
• volume of soil particle
• assumed to be 2.65 Mg m-3
• example on page 59 of text book

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Exam hints

• Know definitions.
• Know formulae for calculating bulk
• density and particle density.
• Remember that particle density is assumed to be
  2.65 Mg m-3

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Soil Formation

• Parent Materials

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Types of rock

• Magma molten rock
• Igneous cold, solid magma
• Sedimentary materials deposited from suspension
  or precipitated from solution
• Metamorphic rocks changed by heat and pressure

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The Rock Cycle (Reeves, 1998)
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Regolith

• Regolith
• Unconsolidated debris from the breakdown of solid
  rock
• May have formed from the rock it now lies on top
  of
• Or been transported from somewhere else
• Varies in thickness

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Parent Material

• Upper layers of regolith have been altered more
  than deeper layers
• Deeper layers are most like the original regolith
• This original regolith is the soil parent material

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Moraine

• An accumulation of earth, usually with stones,
  carried and deposited by a glacier
• heterogeneous
• unsorted and unstratified

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Morainal parent material
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Fluvial deposits

• Deposited by flowing water
• Includes glaciofluvial
• Gravel, sand, and/or silts
• Rounded grains, sorted and stratified

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Fluvial parent material
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Lacustrine deposits

• Deposited in lakes
• Stratified
• Sorted
• Absence of stones - usually

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Lacustrine parent material
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Eolian deposits

• Transported and deposited by wind
• Medium to fine sized sand
• Medium to fine sized silt
• or both sand and silt
• Sorted

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Eolian parent material
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Colluvium

• Moved by gravity
• Heterogeneous mix of sizes
• Unsorted
• Unstratified
• Rock fall

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Colluvium parent material
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Residual parent material

• Formed from rock
• Weathered in place
• Not transported

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Parent material in Canada

• During Ice Ages, Canada was covered by ice.
• The ice scraped off most of the surface and
  moved materials around
• When the ice left, soil formation started all
  over again

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The Laurentide Ice Sheet CoverGodfrey 1993
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Glaciers and parent material

• Glacial till (Also called till)
• Ground moraine
• End moraine
• Recessional moraine
• Lateral moraine

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Glaciers and parent material

• Kettle
• Esker
• Kame
• Outwash plain
• Braided stream
• Drumlin

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Formation and deposition of glacial materials
R. C. Izaurralde Pedosphere.com
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Edmonton region during final stages of
deglaciation (Godfrey, 1998)
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Surface geology of the Edmonton region (Godfrey,
1998). Legend in textbook page 84
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Weathering of Rocks and Minerals
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Weathering of rocks and minerals

• Rocks weather into minerals
• Physical and chemical processes
• Continues until primary particles formed
• Primary particles can be further altered

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Chemical weathering

• Accelerated by the presence of
• water (and its dissolved solutes)
• oxygen
• organic and inorganic acids
• Decomposition

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Chemical weathering

• converts primary minerals into secondary minerals
• e.g. feldspars and micas into clays
• dissolves essential elements out of minerals and
  makes them available to plants and organisms

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Chemical processes

• Carbonation
• Hydration
• Hydrolysis
• Oxidation

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Carbonation

• A chemical weathering process in which dilute
  carbonic acid reacts with a mineral
• Carbonic acid is derived from the solution in
  water of free atmospheric soil-air carbon dioxide

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Carbonation

• Rainwater dissolves CO2 producing carbonic acid.
• This acid can dissolve limestone
• CO2 H2O ? H2CO

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Hydration

• Chemical combination of water with another
  substance
• Mineral plus water forms new mineral
• Ca2SO H2O ? CaSO?2 H2O

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Hydrolysis

• The process by which a substrate is split to
  form two end products by the intervention of a
  molecule of water
• 2HAlSi3O8 11H2O ? Al2O3 6H4SiO4

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Oxidation

• A reaction in which atoms or molecules gain
  oxygen or lose hydrogen or electrons
• Iron plus oxygen produces rust
• Fe2 ? Fe3 electron

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Physical Weathering

• Disintegration
• Temperature
• Water, Ice and Wind
• Plants and Animals

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Temperature

• Daytime heating and night cooling
• Differential heating
• Exfoliation
• Water freezing in cracks

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Water, Ice and Wind

• Cutting power of water
• Water abrasion
• Glaciation
• Wind abrasion

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Plants and Animals

• Roots pry open cracks
• Animals move into and through soil

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Development of Soil
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Parent material and Soil

• Upper part of regolith affected by
• atmosphere
• hydrosphere
• biosphere
• lithosphere
• It is the pedosphere

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Pedosphere

• Upper part of regolith
• 1 to 2 metres
• Can be more, or less
• The place where soil is born

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Soil and Solum

• Soil is part of the regolith
• A and B horizons are part of the solum
• The C horizon is part of the regolith that
  underlies the solum
• The C horizon may be slowly changing into soil in
  its upper parts

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Factors affecting soil formation
Climate (precipitation, temperature) Vegetation
(plants) Parent material (geological/organic) Orga
nisms (soil microbes/fauna) Relief (configuration
of surface)
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Climate

• Temperature
• Precipitation
• Control the rate of weathering processes

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Climate

• Length of growing season
• Length of frost free season
• Amount and intensity of rainfall

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Vegetation

• Type and amount
• pH of the plant material
• Natural or disturbed

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Parent material

• Type
• Resistance to weathering
• Weathering products

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Topography

• The shape of the landscape
• Water moves downslope
• Wind moves material
• Gravity moves material downward
• Controls where materials come from and where they
  are deposited

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Soil Organisms

• Different sizes
• Bacteria
• Fungi
• Microfauna
• Earthworms
• Gophers

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Soil organisms

• Need food
• Need water and air
• Like it warm
• Types and amounts

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Human Impacts

• Alteration of natural vegetation
• Tillage
• Irrigation
• Addition of wastes and fertilizers
• Addition of pollutants

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Soil forming formula
S f (cl, v, pm, r, o)t where s is soil
property, cl is climate, v is vegetation, pm is
parent material,r is relief (topography), and o
is soil organisms.
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The time factor

• t1 time that these natural processes have been
  operating
• t2 time that human management has been
  operating
• Time is not a driving variable

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Horizon Development
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Horizon development

• Takes time
• Develop due to many processes
• Additions
• Removals
• Transfers
• Transformations

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Additions

• Energy from the Sun
• Organic residues
• Carbon dioxide and nitrogen gas
• Gas exchange with the atmosphere
• Water
• Suspended and dissolved materials

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Removals

• By wind and water
• Leaching
• Nutrient uptake
• Gaseous losses

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Mixing

• By fauna and flora
• Shrinking and swelling
• Freezing and thawing

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Translocation

• Soluble minerals
• Colloidal material
• Organic compounds
• Movement up and down
• Within the soil profile

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Transformations

• By chemical reactions
• By biological reactions
• Dissolution and precipitation

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Steady state and change

• Steady state no net change in the system
• Input lt output depletion
• Input gt output accumulation

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Of, Om and Oh horizons

• Organic
• Develop from mosses, rushes, woody materials
• Of least decomposed
• Om intermediate decomposition
• Oh most decomposed

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L, F and H horizons

• Organic
• Develop mainly under forests
• L original material recognizable
• F partly decomposed
• H Original material unrecognizable

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A horizon

• Mineral
• At or near surface
• Removal of materials in solution and suspension
• Maximum accumulation of organic carbon

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B horizon

• Mineral
• Enrichment of silicate clay, iron, aluminum or
  humus
• prismatic, columnar structure with stainings or
  coatings
• alteration by hydrolysis, reduction or oxidation

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C horizon

• Mineral
• Comparatively unaffected by pedogenic processes
• Might be gleyed
• Might have accumulated soluble salts and
  carbonates

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Credit U of A Extension Pedosphere.com
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Horizon suffixes

• Tell us more about the horizon
• lowercase
• See pages 89 and 90 of textbook

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Soils around Edmonton

• Luvisolic order
• Chernozemic order

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Toposequence
A sequence of related soils that differ, one
from the other, primarily because of topography
as a soil-formation factor. See definitions in
Section 5.6
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Catena
If the soils in a toposequence have
developed from the same parent materials, they
may differ on the basis of drainage due
to differences in relief. The latter sequence is
called a catena
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Catena

• Refer to pages 131 to 133 of the text book.
• A catena assignment worth 5 of the course mark
  will be handed out on January 31, 2001.

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Summary

• Parent material, weathering, soil development and
  development of horizons

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Parent material summary

• From different kinds of rocks.
• Weathered by physical and chemical processes.
• Glaciation major impact in Canada

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Weathering Summary

• Physical and chemical processes
• Breakdown into smaller pieces
• Alteration of primary minerals into secondary
  minerals
• Takes time

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Weathering Summary

• Weathering produces
• primary minerals
• secondary minerals (clays)
• oxides,
• organic complexes,
• acids and soluble materials

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Soil Development Summary

• Soils form from parent materials
• Soils develop over time
• Driving variables are climate, vegetation, parent
  material, relief and organisms

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Horizon development summary

• additions
• removals
• mixing
• translocation
• transformation

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Almost done
Please wait
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Assignment 1

• Due at start of class next week.
• Can be e-mailed before that.
• Worth 4
• Pen or word processed, please.
• Good Luck!

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Next Week

• Lecture 2 review
• Types of horizons
• Describing horizons
• Soil forming processes
• Assignment 2 and Catena exercise

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Thats it for this week. Safe trip home