Section M - Soils

What is soil?

a dynamic natural body composed of mineral and organic solids, liquids, and living organisms which can serve as a medium for plant growth

What does soil provide plants with? (4)

• physical support

• nutrients

• water for growth

• plants reduce erosion

How are soils important: (6)

• medium for plant growth

• recycling system for nutrients and organic wastes

• modifier of the atmosphere

• habitat for soil organisms

• engineering medium

• system for water supply and purification

Never treats soils like _

dirt

Soil is composed of: (3)

1. inorganic mineral matter (45%)

2. organic matter (5%)

3. pore spaces (50%)

Inorganic mineral matter

derived from weathered rocks, parent material

Organic matter (3)

• derived from decomposed living matter

• humus

• Chernozemic soil order - 2.5-8.5% OM

What is Humus?

partially decomposed organic matter mixed into surface soil

Pore spaces (3)

• void spaces between solids

• contains air and water

• contains dissolved substances

Soils can be viewed as:

a complex 3D structure, consisting of packed aggregates and pore spaces

Aggregate

Solid, liquid, and gaseous matter in soil are continuously interacting through: (3)

• chemical

• physical

• biological processes

Soils as a dynamic layer consists of matter in all 3 states:

• solid (50%)

• liquid (25%)

• gas (25%)

Soil is studied from _ to _

• surface

• bedrock

Each layer in soil is known as:

soil horizon

Two types of translocation

• eluviation

  • material is removed from a horizon (exit)

• leaching

  • dissolved nutrients are removed from a horizon

Type of addition

illuviation: material is moved into a horizon (in)

Soil horizons: (5)

• o horizon

• a horizon

• b horizon

• c horizon

• r horizon

O horizon

• topmost layer composed of organic matter

  • L, F, H

A horizon

• humus and organic materials mixed with minerals and zone of translocation

  • eluviation

B horizon

• mineral layer strongly influenced

  • illuviation

C horizon

• weathered parent material

  • regolith

R horizon

bedrock

Bedrock

rock that is structurally part of and connected to earth’s crust

Regolith

loose, fragmented earth material that covers bedrock

Parent Material

any material suitable for transformation into soil

Precipitation → _ → soil water storage

infiltration

Soil water classification (3)

• capillary

• hygroscopic

• gravitational water

Soil water availability (2)

• wilting point

• field capacity

Hygroscopic water

remaining water adheres to soil particles and is unavailable to plants

Capillary water

water held in micropores

Gravitational water

drains out of the root zone

When wilting point and field capacity come together:

available water plant roots can absorb it

Pedogenesis is:

the process of soil formation

Additions (3)

• water

• wind

• organic enrichment of A horizon

Transfer/ Translocation (3)

• eluviation

• leaching

• illuviation

Depletion (removal) (2)

• decalcification

• leaching

Transformation

humification

Mixing (2)

• bioturbation

• frost heaving

What are five factors that generally influence soil formation and affect how soils evolve (CLORPT)

• climate

• organism

• relief

• parent material

• time

How climate is a soil-forming factor

temperature and moisture influence the type and rate of biological and chemical reactions in soil

Warm, humid regions lead to:

better developed soils

Moisture dramatically influences:

translocation

Organisms (5)

• native vegetation

• microbes

• soil animals

• human beings

• billions of organisms belonging to thousands of species in a handful of soil

What is relief?

differences between the highs and lows of a landscape

With relief- slope influences soil development (3)

• steep slopes: soils thin and less well developed more erosion due to flowing water and gravity

• level slopes: develop more fully and become thicker

• catena

Parent material

the sediments or rocks in which the soils will form

Types of parent material (5) +examples

• residual- bedrock/ regolith

• glacial till- sediments deposited within or beneath a glacier

• fluvial- sediments deposited by flowing water

• eolian- sediments deposited wind

• lacustrine- sediments deposited in lakes

Soil formation factors: time

A, B horizons may take up to 5,000 years to fully develop

Canadian soils are relatively young due to:

Pleistocene glaciation

As soils forms under a particular set of environmental conditions, it develops _ properties

unique

Soil characteristics can be measured to distinguish:

different soils and to learn something about how they formed

Physical soil characteristics (2)

• texture

• colour

Chemical soil characteristics (3)

• colloids

• cation exchange

• soil pH

Texture characteristics (4)

• sand, silt and clay (size grade)

• loam

Texture affects:

ability of soil to retain water

• clay holds more water than sand

What is loam?

a type of soil that combines sand, silt and clay

Soil colour characteristics + padzol example (4)

• can indicate the composition of the soil

• podzol example:

  • darker O horizon → organic matter

  • white A horizon → eluviated

  • red B horizon → enrichment with Fe, Al

Podzol (2)

• associated with coniferous forest

• distinct horizon development due to abundant chemical transformations

Soil colloids (2-3)

• smallest and most chemically active particles in soils <0.000,01 mm

  • clay minerals

  • organic matter

• -ve surfave charge attracts +ve cations

  • soil nutrients

Soil colloids have high _ holding capacity

h₂o

Cation exchange

total amount of exchangeable cations that a soil can absorb

Soil pH (3)

• concentration of hydrogen ions present in soil solution

• important indicator of soil fertility

  • most nutrients readily available between 6.5-7.5

What is taxonomy?

Canadian system of soil classification

Ten soil orders

• Brunisolic (forest)

• Chernozemic (grassland)

• Cryosolic (tundra)

• Gelysolic (g)

• Luvisolic (f,g)

• Organic (f)

• Podzolic (f)

• Solonetzic (g)

• Verticolic (g)

Chernozemic order

• prairie soils

• highly productive

• surface horizons darkened by the accumulation of organic matter (om)

  • ah at least 10cm

  • colour brown -dark black

Chernozemic soils: great groups reflect:

climate differences

Gleysolic order

• periodic or prolonged saturation with water and anaerobic conditions

  • reducing conditions

• associated with high ground water table

  • depressions or sloughs

Diagnostic features (2)

• poorly drained soils

• gleyed features