Soil 101Everything you need to

know!

Ms. Brown

Part 2: Understanding Soil Formation

Identify five factors involved in soil formation.

Parent material: Type of rock material the soil is formed from.

Climate: Temperature and moisture characteristics of the area in which the soil was formed.

Living organisms: The organisms, including plant material, that live within the soil.

Topography: Slope characteristics of the soilTime or weathering: Age of the soil and its

climate.

Types of Parent Material

• Parent materials are formed by the disintegration and decomposition of rock.

• They are classified according to the way they were moved and scattered.

Types of Parent MaterialGlacial Origins

Loess

Outwash

Glacial Till

Alluvium

occurred from the blowing of the soil after the glaciers melted and dried. well-balanced mineral content, medium texture, and excellent water-holding capacity, Most Desirable Parent Material

occurred when the glaciers melted.The melt waters carried the gravelly materials away to be deposited below the glacial ridges. Sandy outwash was carried further downstream and the finer materials, silt and clay, were deposited in lakebeds or slow moving water along streams.

variety of sizes of soil particles.These soil particles have not been layered from the effects of wind or water

recent sediments deposited by streams as they flood.Alluvium is generally a water-borne material deposited on bottomlands

Bed Rock

• Bedrock most of the shale, sandstone, or limestone bedrock is buried by loess, glacial till, outwash, or alluvium.

• However, in the unglaciated areas weathered bedrock has provided soil parent material.

Organic Matter

• Organic matter: Organic soils occur where formerly shallow ponds supported swamp vegetation. – The wet conditions slowed decay of the

dead plants so that organic matter could accumulate.– The two types of organic soils are referred

to as peat and muck. –Muck is more decomposed than peat

How Topography Affects Soil Formation

• Topography refers to the slope characteristics of a soil.

• It includes the degree or steepness, length, shape, and direction of a slope.

• These factors influence the amount of rainwater runoff, or the amount that enters the soil or collects in small depressions on the soil surface.

• Soils on steep slopes have higher amounts of runoff and erosion than those on level topography.

How Organisms Affect Soil Development

• Two types of native vegetation: – tall prairie grass --- prairie soils – deciduous-hardwood forests--timber soils.

• Prairie soils have a dark and deep surface layer. • This is because roots from the prairie grass filled

the top of the soil to a depth of 1 to 2 feet or more.

• Partial decay of these roots over a long period of time gave these soils a high organic matter content.

How Organisms Affect Soil Development

• Timber soils tend to have a thin, moderately dark layer. • This is due to organic matter accumulating on the

surface where decay occurs more rapidly. – When tilled, this dark material is mixed with the soil below

to produce a lighter color.• Other living matter that influences the development of

soil includes various kinds of animal life. • Earthworms, crawfish, ground squirrels and other

burrowing animals, and various insects which incorporate organic matter into the soil are examples.

Types of WeatheringChemical Weather Physical Weathering

Chemical weathering changes the chemical makeup of rock and breaks it down.Rainwater is mildly acidic, and can slowly dissolve many soil minerals.

Some minerals react with oxygen in the atmosphere. Oxidation further acts to decompose rock.

Physical weathering the effects of climatic factors such as temperature, water, and wind. Freezing and thawing is a major contributor to physical weathering.

• Weathering causes soil to:

–Develop rapidly, plant nutrients are released, and organic matter accumulates. • Soils will develop faster in humid

regions than in arid regions.

– Mature soil is at peak productivity with a high amount of organic matter. • Water begins leaching away nutrients and plant growth

starts to decline. • This results in less organic matter.

– Minerals continue to break down and clay is leached into the subsoil. • The soil becomes lighter in color from less organic

matter.

How Climate Affects Soil Development

• Climate refers to rainfall, freezing, thawing, wind, and sunlight.– These factors are either directly or indirectly

responsible for the breakdown of rocks and minerals, the release of plant nutrients, and many other processes affecting the development of soils.

What is Soil Texture?

• Soil texture is the fineness or coarseness of a soil.

• It describes the proportion of three sizes of soil particles. These are:– Sand - large particle– Silt - medium sized particle– Clay - small particle

What does Texture Affect?

• Soil workability the ease with which soil may be tilled and the timing of working the soil after a rain

• Ability of plants to grow some root crops like carrots and onions will have difficulty growing in a fine-textured soil

Determining Soil Texture

• Soil texture may be determined in one of two ways:– The percentages of sand, silt, and clay may be

tested in the lab. • Once tested, you may determine the textural class of

the soil by referring to the textural triangle.– The ribbon method.

Notice the

Shape and Size of the These

Soil Particle Types

Textural TriangleUnderstanding the

Textural Triangle and Determining

Soil Texture

Worksheet: Part 1

LAB TIME!!!

• Determining Soil Texture by the Ribbon Method

Soil ProfilesWhat is a Soil Profile?

• A soil profile is a vertical cross-section of the soil. – When exposed, various layers of soil should be apparent.

• Each layer of soil may be different from the rest in a physical or chemical way. – The differences are developed from the interaction of

such soil-forming factors as:• Parent material• Slope• Weathering (time) • Climate• Native vegetation

A soil profile is usually studied to a

depth of 3 to 5 feet.

What are the major horizons of a soil profile and how do they differ?• There are 3 primary soil horizons called

master horizons.

–A Horizon

–B Horizon

–C Horizon

A Horizon.

This is often referred to as topsoil and is the surface layer where organic matter accumulates. Over time, this layer loses clay, iron, and other materials due to leaching. This is called eluviation. The A horizon provides the best environment for the growth of plant roots, microorganisms, and other life.

• O Horizon. – This is an organic

layer made up of partially decayed plant and animal debris.

– It generally occurs in undisturbed soil such as in a forest.

B Horizon. This horizon is

referred to as the subsoil.

It is often called the “zone of

accumulation” since chemicals

leached from the A and E horizons

accumulate here.

• E Horizon.• This is the zone of

greatest eluviation. – Because the clay,

chemicals, and organic matter are very leached, the color of the E horizon is very light.

– It usually occurs in sandy forest soils with high amounts of rainfall.

B Horizon

– This accumulation is called illuviation. The B horizon will have less organic matter and more clay than the A horizon.

– Together, the A, E, and B horizons are known as the solum.

– This is where most of the plant roots grow.

C Horizon

• This horizon is referred to as the substratum. – It lacks the properties of the A and B horizons

since it is influenced less by the soil forming processes.

– It is usually the parent material of the soil.

R Horizon

• This is the underlying bedrock, such as limestone, sandstone, or granite.– It is found beneath the C horizon.

Soil Profile Horizons

• O Horizon organic layer of leaves, roots,and decaying material

• A Horizon Topsoil• B Horizon Subsoil• C Horizon Substratum• R Horizon Bedrock or solid rock

below the C Horizon

How do soils within a soil profile change over time?

• Soils change over time in response to their environment.

• The environment is influenced by the soil-forming factors.

The causes of these changes can be classified into 4 processes:

– Additions. Materials such as fallen leaves, wind-blown dust, or chemicals from air pollution that may be added to the soil.

– Losses. Materials may be lost from the soil as a result of deep leaching or erosion from the surface.

– Translocations. Materials may be moved within the soil. • This can occur with deeper leaching into the soil or upward

movement caused by evaporating water

– Transformations. Materials may be altered in the soil. • Examples include organic matter decay, weathering of

minerals to smaller particles, or chemical reactions.

Understanding Soil Color

• What are physical features used to differentiate between soils?– Texture coarseness or fineness of soil

particles– Structure the way in which soil particles are

held together–Depth of horizons the depth of each soil–Color refers to the darkness or lightness of

the soil color

What are the colors used to describe surface soils?

• Colors associated with surface soils are dependent on the amount of organic matter found in them.

• Colors may be classified as:– Very Dark: approximately 5% organic matter– Dark approximately 3.5% organic matter– Moderately dark approximately 2.5% organic matter– Light approximately 2% organic matter– Very light approximately 1.5% organic matter

The amount of organic matter is the factor used to determine the color of the surface soil.

The amount of organic matter is determined by the kind of native vegetation.

Native vegetation refers to the type of plant material that grew on the soil.

What colors are used to describe subsoil?

• Subsoil colors are associated with natural drainage of the soils.

• This is the drainage condition that existed when the soil was forming.

• Subsoil colors are classified as:– Bright-colored brown, reddish brown, or

yellowish brown– Dull-colored gray or olive gray–Mottle-colored clumps of both bright and dull

colors mixed together

What factors determine the color of subsoil?

• The color of subsoil is determined by the status of iron compounds.

• These are determined by the type of drainage found in the soil as it formed. Good drainage provides subsoil that is bright in color.

• This is because the iron found in these soils has been oxidized.

• This can be compared to metal that oxidizes or rusts when both moisture and air are present.

• Rust has a bright or orange color.

What factors determine the color of subsoil?

• Poor drainage provides subsoil that is dull or gray in color.

• This is because the iron found in those soils has not been subject to air or oxygen.

• The iron compounds do not oxidize. • This leaves a grayish color.

What factors determine the color of subsoil?

• Somewhat poor drainage provides subsoils that are mottled.

• This is because the soil was saturated with moisture for certain periods.

• This leaves a gray color in some soil clumps. • Since the soil was comparatively dry during

other periods, it left a bright color in other soil clumps.

How do parent material, age, and slope affect the color of soil?

• In addition to organic matter and drainage, soil color may also be affected by other factors:– parent material– age– slope

Age As soils age, much of the darker color is lost due to the weathering process. This causes the soil to lose organic matter.Slope Soil on top of hills is usually lighter in color than the soil in depressions or on level ground.This is partly due to the darker topsoil being washed off the hills. This leaves the lighter subsurface or subsoil exposed.

Parent Material • The color of a soil is

associated with the kind of material from which it is formed.

• Soils that are developed from sand or light-colored rock will be lighter.

• Those developed from darker materials such as peat or muck, will be darker in color.

Lab Time

• Making Your Own Soil Profile

• Part 1: Illustrating the Soil Profile You are creating!

• Part 2: Creating your Own Edible Soil Profile

Understanding Water Holding Ability

• What is Moisture holding Capacity?– Moisture holding capacity is the ability of the soil

within the soil profile to retain water.

What is available to the plants?

• Available soil moisture is the water in the soil that can be used by plants. –When moisture levels are high, plants can

easily extract moisture from the soil. –As the water is used, soil moisture tension

increases. • Soil moisture tension is the force by

which soil particles hold on to moisture.

How do we determine how much moisture the soil can hold?

• Moisture holding capacity is determined primarily by the soils texture.– As a rule, the finer the texture of the soil, the more moisture

it will hold.– A soil high in sand will hold less water.– Soils high in clay, hold water and keep it from percolating out

of the root zone.– If the soil is entirely clay, it will hold the water too tightly. – This means less water is available to plants than if silt were

present.– A good silt loam holds the most moisture available for plants

• The amount of moisture the soil can hold for plants is referred to as available water holding capacity.

Available water holding capacity depends on:

• 1. How deep the soil profile is.• 2. The type of soil texture found

throughout the soil profile. – On average, the following textures will hold the

designated amount of moisture per inch of soil:– fine textured .20 inches– moderately fine textured .25 inches – medium textured .30 inches – moderately coarse textured .20 inches – coarse textured .10 inches

How do you know figure the water holding capacity

• To determine the available water holding capacity for a given area, multiply the depth of each horizon, to a maximum depth of 60 inches, by the amount of water the texture within that horizon can hold.

• Add the totals for each horizon to calculate total water holding capacity.

Example

• A horizon: 9 inches deep, medium texture = 9 × .30 =2.70 inches

• B horizon: 23 inches deep, moderately fine texture = 23 × .25 = 5.75 inches

• C horizon: 28 inches deep, medium texture = 28 x .30 = 8.40 inches

• Total = 16.85 inches of water

Water Holding Experiment!

• 1 Jar of Sand, I Jar of Black Soil: Which do you think will hold more water? Why?

• LAB: We have 3 Different Soils we are going to test the water holding capacity of:– Sandy– Clayey – Loamy

Understanding Soil Degradation

• Soil degradation is a lowering of the quality of soil or the loss of soil productivity.

• Soil degradation occurs because people do not understand soil and the consequences of certain of its uses.

• Minimizing soil degradation is important in maintaining a good environment.

• Soil degradation results from:– Construction– Contamination– Erosion

How can construction result in soil degradation?

• Construction is altering land by building:– Roads– Houses– Offices– Factories– Other structures

• Construction degrades the soil by replacing productive land with structures that prevent the production of plants or animals.

• Construction degrades the soil when native grasses and trees are removed.

• This leaves the soil unprotected from erosion.

Construction and Soil Degradation• Large equipment may move topsoil around and cover it

with subsoil.• Soil can be compacted when wet by heavy equipment.• Digging deep into the earth brings up subsoil and parent

material. • When it is spread on the surface, fertility is lowered.• Native grasses and trees are removed leaving soil

unprotected from erosion.• Topsoil is covered with subsoil.• Soil is compacted and mashed into deep ruts when it is

wet.• Digging deep into the earth brings up parent material and

subsoil that is spread on the surface, lowering the fertility.

What are the sources of contamination and how do they result in soil degradation?

• Contamination results when chemicals, oil, and other substances leak into the land.

• Some contaminants soak into the soil and destroy its ability to support plant growth.

• Other materials may pass through the soil and enter the ground water.

• This can contaminate water supplies.• Land formerly used as dumps, mines, and factory sites

may be rehabilitated. • This involves removing contaminated soil and covering

what remains with non contaminated soil. – This process is expensive.

…Continued

• Land formerly used as dumps, mines, and factory sites may be rehabilitated.

• This involves removing contaminated soil and covering what remains with non contaminated soil. – This process is expensive.

• Soil may be contaminated by agricultural practices, such as:– Use of too much fertilizer.– Use of excess chemicals.– Use of irrigation water containing salt

• Soil erosion is the process by which soil is moved.

Natural causes • Natural erosion shapes the earth’s

landscape by rounding off mountains and filling in valleys which may form new, highly fertile areas. –An example is the Mississippi River Delta.

What is soil erosion and how does it result in soil degradation?

Soil Erosion Continued

Human actions • Human activity, such as construction and

plowing may cause accelerated erosion, which removes topsoil at an excessive rate. – In many places, soil is being lost faster than

it is being formed. • This will result in loss of soil fertility and

productivity.

What are other sources of soil degradation?

• Improper irrigation practices• Growing crops without replacing plant nutrients • Pollution of soils with chemicals, industrial waste,

human waste and livestock waste• Overgrazing and deforestation• Compaction• Improper irrigation practices result in salinization,

alkalization and water logging.• Salinization is an accumulation of soluble salts. • Alkalization is an accumulation of exchangeable sodium. • Both of these are harmful to plant growth

Other Sources of Soil Degradation

• Growing crops without replacing plant nutrients and soil organic matter.

• These soils are “mined” of nutrients.• As fertility drops, soil organic matter is lost and

soil structure deteriorates.• Pollution of soils with chemicals, industrial waste,

human waste and improperly handled livestock waste.

• A large accumulation of heavy metals, salts or an acute accumulation of chemicals can render soil unproductive.

• Overgrazing, deforestation and other practices that remove productive plant cover cause a condition called desertification. – This problem is most common in low rainfall areas.

• Humus content and fertility drops. • Surface soil is exposed and becomes subject to

erosion.• Compaction is the packing of soil particles tightly

together after years of tillage with heavy machinery.

• It can break down soil structure.• Plant growth is reduced, organic matter drops,

permeability is lost, and runoff increases.

Doing the Research!