introduction to soil science

Introduction to Soil Introduction to Soil ScienceScience

By: By:

Sheldon HannSheldon Hann

Soil and Land Resource Soil and Land Resource TechnicianTechnician

Agriculture and Agri-Food CanadaAgriculture and Agri-Food Canada

Email: Email: [email protected]@agr.gc.ca

OutlineOutline

Importance of SoilImportance of Soil

Function of SoilFunction of Soil

Soil Forming Soil Forming FactorsFactors

Soil Forming Soil Forming ProcessesProcesses

Soil PropertiesSoil Properties Soil HorizonsSoil Horizons

Soil DrainageSoil Drainage

Alternate/Alternate/Renewable Energy Renewable Energy and Soil and Soil

Soil Not DirtSoil Not Dirt

Soil:Soil: The top layer of the The top layer of the earth’s surface, earth’s surface,

containing containing unconsolidated rock and unconsolidated rock and

mineral particles mineral particles mixed mixed with organic with organic material.material.

Dirt:Dirt: Misplaced soil.Misplaced soil.

ImportanceImportance

““Soil is the essence of life.”Soil is the essence of life.” Most life on earth depends upon the soil as a direct or Most life on earth depends upon the soil as a direct or

indirect source of food, water and shelter.indirect source of food, water and shelter.

Soil is home to billions of organisms.Soil is home to billions of organisms.

(1ha of land ~ 25 million insects and 1million (1ha of land ~ 25 million insects and 1million earthworms)earthworms)

Soil takes 1000’s of years to develop and is destroyed Soil takes 1000’s of years to develop and is destroyed easily, so it must be conserved in order to continue to easily, so it must be conserved in order to continue to support life. support life.

10mm of soil takes between 100 to 1000 years to form.10mm of soil takes between 100 to 1000 years to form.

FunctionFunction

The function of soil includes:The function of soil includes:

1.1. A medium for plant growth.A medium for plant growth.

2.2. A regulator of water supply.A regulator of water supply.

3.3. Habitat for organisms. Habitat for organisms.

4.4. A recycler of wastes.A recycler of wastes.

5.5. Support of structuresSupport of structures

FunctionFunction

Medium for plant growth:Medium for plant growth: Soil is a source of macro and Soil is a source of macro and

micronutrients.micronutrients. Macronutrients include nitrogen, Macronutrients include nitrogen,

phosphorous, potassium, nitrogen, etc.phosphorous, potassium, nitrogen, etc. Micronutrients include iron, manganese, Micronutrients include iron, manganese,

zinc, copper, etc.zinc, copper, etc.

Soil is a source of water and Soil is a source of water and nutrients for plants during the nutrients for plants during the growing season.growing season.

Soil anchors plants, which increases Soil anchors plants, which increases the stability of the soil.the stability of the soil.

FunctionFunction

Regulate water supply:Regulate water supply: Soil plays a vital role in Soil plays a vital role in

cycling freshwater.cycling freshwater.

Soil filters and regulates the Soil filters and regulates the water supply by storing water supply by storing water after a precipitation water after a precipitation event.event.

This stored water can then This stored water can then be released during the be released during the growing season, to minimize growing season, to minimize drought.drought.

FunctionFunction

Habitat for organisms:Habitat for organisms: Soil is composed of billions of organisms.Soil is composed of billions of organisms.

These organisms decompose organic matter These organisms decompose organic matter and convert minerals and nutrients into and convert minerals and nutrients into forms that are available to plants and forms that are available to plants and animals.animals.

FunctionFunction

Recycle wastes:Recycle wastes: Soil has the ability to recycle natural wastes, Soil has the ability to recycle natural wastes,

if these wastes are added in appropriate if these wastes are added in appropriate amounts.amounts.

Plant residues and manure can be added to Plant residues and manure can be added to soil which will enrich nutrient concentrations soil which will enrich nutrient concentrations and may improve soil properties.and may improve soil properties.

FunctionFunction

Support for Support for structures:structures:

Soil is used for structures Soil is used for structures such as roads, causeways such as roads, causeways and as the foundation for and as the foundation for buildings and bridges.buildings and bridges.

Soil is used for the Soil is used for the establishment of forestry establishment of forestry and agriculture crops.and agriculture crops.

Soil Forming FactorsSoil Forming Factors

The soil forming factors include:The soil forming factors include:

Soil Formation

Climate

Vegetation

Parent Material

Soil Organisms

Topography

Time


Climate:Climate: Temperature and Temperature and

precipitation control precipitation control the rate of weathering.the rate of weathering.

In arctic and desert In arctic and desert areas soils develop areas soils develop more slowly than in more slowly than in hot, wet climates.hot, wet climates.


Vegetation:Vegetation: The type of vegetation influences the type The type of vegetation influences the type

and amount of organic material that is and amount of organic material that is added to the soil.added to the soil.

Organic additions in a prairie ecosystem Organic additions in a prairie ecosystem will be in the form of grass roots.will be in the form of grass roots.

Organic additions in a boreal forest will be Organic additions in a boreal forest will be in the form of fallen plants, needles and in the form of fallen plants, needles and leaves.leaves.


Parent Material:Parent Material: Soil is highly dependant on the existing Soil is highly dependant on the existing

parent material.parent material.

Some parent materials will weather more Some parent materials will weather more readily than others.readily than others.

Soil developed on sandy material differs Soil developed on sandy material differs from soil developed on clay deposits. from soil developed on clay deposits.


Soil Organisms:Soil Organisms: Soil organisms control decomposition rates Soil organisms control decomposition rates

and nutrient cycling.and nutrient cycling.

Bacteria, fungi and microbiota convert Bacteria, fungi and microbiota convert organic substances into soil.organic substances into soil.

Earthworms increase aeration and change Earthworms increase aeration and change the structure of the soil.the structure of the soil.


Topography:Topography: The physical shape of the landscape The physical shape of the landscape

determines how much soil material is determines how much soil material is relocated by water, wind and gravity.relocated by water, wind and gravity.

Topography also determines the patterns of Topography also determines the patterns of the relocated soil.the relocated soil.


Time:Time: Soils are dynamic, continuously changing Soils are dynamic, continuously changing

overtime.overtime.

The development of soil takes hundreds of The development of soil takes hundreds of years, therefore the time that has elapsed is years, therefore the time that has elapsed is an important factor.an important factor.

The longer the time a soil has been forming, The longer the time a soil has been forming, the more highly developed that soil will be.the more highly developed that soil will be.

Soil Forming ProcessesSoil Forming Processes

The soil forming processes include:The soil forming processes include: Chemical weatheringChemical weathering

Physical weatheringPhysical weathering

Biological weatheringBiological weathering


Chemical weathering:Chemical weathering:

Caused by the chemical action of water, Caused by the chemical action of water, oxygen, carbon dioxide and organic acids.oxygen, carbon dioxide and organic acids.

An examples of chemical weathering is An examples of chemical weathering is oxidation.oxidation.


Physical weathering:Physical weathering: Also known as “disintegration”, whereby the Also known as “disintegration”, whereby the

size of rock and soil particles are reduced size of rock and soil particles are reduced without changing the chemical make-up of without changing the chemical make-up of the particles.the particles.

An example of physical weathering would be An example of physical weathering would be frost wedging.frost wedging.


Biological weatheringBiological weathering::

Organisms can assist in the breakdown and Organisms can assist in the breakdown and formation of sediment and soil.formation of sediment and soil.

Examples of biological weathering are:Examples of biological weathering are: Root weatheringRoot weathering Organic weatheringOrganic weathering

Soil PropertiesSoil Properties

Soil properties include:Soil properties include: TextureTexture Organic matterOrganic matter ColorColor StructureStructure ConsistenceConsistence Cation exchange capacityCation exchange capacity pHpH


Texture:Texture: Refers to the proportions of sand, silt and Refers to the proportions of sand, silt and

clay found in a given soil.clay found in a given soil.

Different combinations of sand, silt and clay give Different combinations of sand, silt and clay give rise to soil texture classes.rise to soil texture classes.

Soil Soil SeparateSeparate

Diameter Diameter (mm)(mm)

SandSand 2.0 - 0.052.0 - 0.05

SiltSilt 0.05 - 0.0020.05 - 0.002

ClayClay < 0.002< 0.002


Texture Classes:Texture Classes:

* Loam is a soil that has an even mixture of sand, silt * Loam is a soil that has an even mixture of sand, silt and clay.and clay.

Texture ClassTexture Class DescriptionDescription

SS SandSand

LSLS Loamy SandLoamy Sand

SLSL Sandy LoamSandy Loam

LL LoamLoam

SiLSiL Silty LoamSilty Loam

SCLSCL Sandy Clay LoamSandy Clay Loam

CLCL Clay LoamClay Loam

CC ClayClay

Coarse

Fine


Organic Matter:Organic Matter:

Increases the soil’s ability Increases the soil’s ability to hold water and to hold water and nutrients.nutrients.

Affects pore size and Affects pore size and helps control the flow of helps control the flow of water and air into the water and air into the soil.soil. Generally organic matter content in soil decreases Generally organic matter content in soil decreases with soil depth.with soil depth.

Productivity increases as organic matter within Productivity increases as organic matter within the soil increases.the soil increases.


Color:Color: Can be used to understand parent material of the Can be used to understand parent material of the

soil, the soil drainage, amount of iron and organic soil, the soil drainage, amount of iron and organic matter in soil.matter in soil. Soils that come from siltstones have a olive-gray color and Soils that come from siltstones have a olive-gray color and

those that come from sandstones have a yellowish-brown those that come from sandstones have a yellowish-brown color.color.

Generally soils with good drainage have bright colors.Generally soils with good drainage have bright colors.

Dark brown or black colors suggest high levels of organic Dark brown or black colors suggest high levels of organic matter.matter.

Soil color is described by using the Munsell color Soil color is described by using the Munsell color charts.charts.


Structure:Structure: Structure influences the movement of water Structure influences the movement of water

and gas through soils.and gas through soils. Soil particles that are held together by Soil particles that are held together by

chemical and physical forces are called chemical and physical forces are called “peds”.“peds”.

The types of soil peds define soil structure.The types of soil peds define soil structure. Structure is classified by describing:Structure is classified by describing:

Distinctiveness – structure of peds.Distinctiveness – structure of peds. Size – size of peds.Size – size of peds. Shape – shape of peds.Shape – shape of peds.


Consistence:Consistence: Relates to soil strength, the resistance of the Relates to soil strength, the resistance of the

soil to breaking.soil to breaking.

Influences soil aeration and water movement Influences soil aeration and water movement through the soil and how the soil will respond through the soil and how the soil will respond to surface traffic and root penetration.to surface traffic and root penetration.

By crushing a soil ped in your hand soil By crushing a soil ped in your hand soil consistence can be determined.consistence can be determined.


Consistence:Consistence:

The classes of consistence for moist soil are:The classes of consistence for moist soil are:

Loose - Loose - Non-coherentNon-coherent

Very Very Friable - Friable -

Soil crushes under very gentle pressure, but Soil crushes under very gentle pressure, but keeps a form when pressed together.keeps a form when pressed together.

Friable - Friable - Soil crushes under very gentle to moderate Soil crushes under very gentle to moderate pressure, but keeps a form when pressed pressure, but keeps a form when pressed together.together.

Firm - Firm - Soil is hard to crush under moderate pressureSoil is hard to crush under moderate pressure

Very Firm - Very Firm - Soil crushes under strong pressure, barely Soil crushes under strong pressure, barely crushable.crushable.


Cation exchange capacity (CEC):Cation exchange capacity (CEC): A measurement of a soil’s ability to attract and A measurement of a soil’s ability to attract and

hold positively charged ions (cations) at a given hold positively charged ions (cations) at a given pH.pH.

Determined by the amount and type of clay and Determined by the amount and type of clay and organic material that is present in the soil.organic material that is present in the soil.

Some examples of the major nutrients that are Some examples of the major nutrients that are held in soil by CEC are:held in soil by CEC are:

CalciumCalcium

MagnesiumMagnesium

IronIron

PotassiumPotassium


Cation exchange capacity (CEC):Cation exchange capacity (CEC): The more clay particles and organic The more clay particles and organic

materials found in the soil, the higher the materials found in the soil, the higher the CEC.CEC.

Soils with high CEC are better at holding soil Soils with high CEC are better at holding soil nutrients.nutrients.

Soils with low CEC tend to be less fertile Soils with low CEC tend to be less fertile then soils with high CEC, because of nutrient then soils with high CEC, because of nutrient holding capacity.holding capacity.


pH:pH: A measure of the acidity or alkalinity of soil A measure of the acidity or alkalinity of soil

and is measured in pH units.and is measured in pH units.

pH scale goes from 0 (acidic) to 14 (basic) pH scale goes from 0 (acidic) to 14 (basic) with pH 7 as the neutral point.with pH 7 as the neutral point.

Most soils have pH values between 4 and 8.Most soils have pH values between 4 and 8.

The solubility of minerals and nutrients in The solubility of minerals and nutrients in soil is highly dependent on the pH of that soil is highly dependent on the pH of that soil. soil.


pH:pH: pH can also influence plant growth by pH can also influence plant growth by

affecting the activity of soil microorganisms.affecting the activity of soil microorganisms.

Bacteria that decompose organic matter are Bacteria that decompose organic matter are hindered in strongly acidic or strongly basic hindered in strongly acidic or strongly basic soils.soils.

This can result in a build-up of organic This can result in a build-up of organic matter and decrease soil fertility.matter and decrease soil fertility.

Soil HorizonsSoil Horizons

Soil Horizons:Soil Horizons: Soil may consist of five Soil may consist of five

horizons:horizons:1.1. Forest floorForest floor

2.2. A horizon – zone of loss.A horizon – zone of loss.

3.3. B horizon – zone of B horizon – zone of accumulationaccumulation

4.4. C horizon – relatively C horizon – relatively unaltered parent unaltered parent materialmaterial

5.5. R - bedrockR - bedrock

Forest floor

A

B

C


Soil Horizons – Forest floor:Soil Horizons – Forest floor: The forest floor consists of:The forest floor consists of:

L (Litter layer) – Found on the ground surface and is L (Litter layer) – Found on the ground surface and is composed of needles, leaves, twigs and other organic composed of needles, leaves, twigs and other organic materials.materials.

F (Fermented layer) – Partially decomposed organic F (Fermented layer) – Partially decomposed organic materials such as needles, leaves and twigs.materials such as needles, leaves and twigs.

H (Humus layer) – Fully decomposed organic H (Humus layer) – Fully decomposed organic material, often black-brown to nearly black in color.material, often black-brown to nearly black in color.


Soil Horizons – A horizon:Soil Horizons – A horizon: Due to biological activity, Due to biological activity,

organic matter has organic matter has accumulated in this accumulated in this horizon resulting in a Ah horizon resulting in a Ah layer.layer.

Horizon that is identifiable Horizon that is identifiable by the absence of clay, by the absence of clay, iron, aluminum and iron, aluminum and organic matter, resulting organic matter, resulting in a Ae layerin a Ae layer

Ah

Ae


Soil Horizons – B Soil Horizons – B horizon:horizon:

Can be characterized by one Can be characterized by one or more of the following:or more of the following: Enriched with clay, iron, Enriched with clay, iron,

aluminum or humus, resulting aluminum or humus, resulting in a Bf layer.in a Bf layer.

An alteration by hydrolysis, An alteration by hydrolysis, reduction or oxidation to give reduction or oxidation to give a change in color or structure a change in color or structure from above or below. from above or below. Resulting in a Bm layer.Resulting in a Bm layer.

Bf

BC


Soil Horizons – C Soil Horizons – C horizon:horizon:

Can be characterized Can be characterized as parent material, as parent material, relatively unaffected by relatively unaffected by the soil forming the soil forming processes. processes.

C


Drainage is defined by the length of time it Drainage is defined by the length of time it takes water to be removed from the soil in takes water to be removed from the soil in relation to the supply.relation to the supply.

Drainage is affected by:Drainage is affected by:

1.1. Soil-External FactorsSoil-External Factors

2.2. Soil-Internal FactorsSoil-Internal Factors


External FactorsExternal Factors Position on the slope – soils in upper positions tend to Position on the slope – soils in upper positions tend to

be better drained than those in the lower slopes.be better drained than those in the lower slopes.

Aspect – Southern aspects are warmer than northern Aspect – Southern aspects are warmer than northern aspects, therefore southern aspects will have less soil aspects, therefore southern aspects will have less soil water and better drainage.water and better drainage.

Climate – Areas that receive high amounts of rainfall Climate – Areas that receive high amounts of rainfall will have poorer drainage than those that receive low will have poorer drainage than those that receive low amounts.amounts.

Bedrock – The presence and type of bedrock can Bedrock – The presence and type of bedrock can affect the rate and the flow direction of soil water.affect the rate and the flow direction of soil water.


Internal FactorsInternal Factors Soil texture – Coarse to medium textured Soil texture – Coarse to medium textured

soils will tend to have better drainage.soils will tend to have better drainage.

Stoniness – Soils with gravels and cobbles Stoniness – Soils with gravels and cobbles have a improved drainage.have a improved drainage.

Consistence – Soils with loose and friable Consistence – Soils with loose and friable consistence will have better drainage than consistence will have better drainage than those with firm and very firm consistence.those with firm and very firm consistence.


Drainage ClassesDrainage Classes Six classes:Six classes:

1.1. RapidlyRapidly

2.2. WellWell

3.3. Moderately WellModerately Well

Soils with good drainage tend to have bright Soils with good drainage tend to have bright colors.colors.

Soils with poor drainage tend to have a Soils with poor drainage tend to have a grayish color.grayish color.

4.4. ImperfectlyImperfectly

5.5. PoorlyPoorly

6.6. Very PoorlyVery Poorly

Alternate / Renewable Alternate / Renewable EnergyEnergy

Soil is important for the production of Soil is important for the production of alternate / renewable energy sources.alternate / renewable energy sources.

Some examples of alternate/renewable Some examples of alternate/renewable energy sources are as follows:energy sources are as follows:

1.1. Biomass EnergyBiomass Energy

2.2. Wind EnergyWind Energy

3.3. Geothermal EnergyGeothermal Energy


Biomass EnergyBiomass Energy Soil provides the minerals and nutrients to the crops Soil provides the minerals and nutrients to the crops

that produce biomass energy.that produce biomass energy.

Biomass is solar energy stored as organic matter. Biomass is solar energy stored as organic matter.

Examples of biomass energy are:Examples of biomass energy are:1.1. Tree and grass crops – firewood and switchgrass are Tree and grass crops – firewood and switchgrass are

two sources of renewable energy that can be easily two sources of renewable energy that can be easily managed.managed.

2.2. Forestry, agricultural and urban wastes – such as Forestry, agricultural and urban wastes – such as residual plant waste and manure can be used as a residual plant waste and manure can be used as a energy source.energy source.


Wind EnergyWind Energy Soil provides the foundation and anchoring for Soil provides the foundation and anchoring for

the wind turbines that produce wind energy.the wind turbines that produce wind energy.

Extensive planning must be done prior to the Extensive planning must be done prior to the establishment of wind energy stations to establishment of wind energy stations to minimize the risk of soil erosion.minimize the risk of soil erosion.

Recognizing the areas that have soil textures Recognizing the areas that have soil textures and structures that may increase soil erosion and structures that may increase soil erosion and therefore be unsuitable for wind energy and therefore be unsuitable for wind energy stations is very important. stations is very important.


Geothermal EnergyGeothermal Energy The temperature of the soil stays relatively The temperature of the soil stays relatively

constant all year round (7-14 degrees C constant all year round (7-14 degrees C depending on location).depending on location).

Geothermal heat pumps and ground loops Geothermal heat pumps and ground loops can be used to capture this consistent can be used to capture this consistent temperature and distribute it to buildings.temperature and distribute it to buildings.

This system can be used for both the This system can be used for both the purposes of heating and cooling.purposes of heating and cooling.

Thank youThank you

Questions?Questions?

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