Animal, Plant & Soil Science
Lesson D1-2
Soil Formation
Interest Approach
 Ask two students to sit or stand in front of the class. Ask the
class if the students are exactly the same. Responses should be
a resounding “No!” Ask the class what makes the students
different from each other. One of the first responses should be
that they have different parents. Relate this to different types
of soil parent material. An additional answer should be that
the students have grown up in different environments and
have had different experiences. Relate this to different
environments in which soils develop. You may even wish to
ask students to think about identical twins who may have
been separated as youngsters. As adults, there will be
differences between them. Explain that even though the twins
have the same genetic makeup, they have experienced
different environments and situations. Relate the same
concept to soil development.
Objectives
 1 Identify five factors involved in soil formation.
 2 Describe different types of parent material.
 3 Explain topography and how it affects soil formation.
 4 Explain how organisms affect soil development.
 5 Describe how time and weathering affect properties of
soil.
 6 Examine how climate affects the development of soil.
Terms
 alluvium
 organic matter
 bedrock
 outwash
 chemical weathering
 parent material
 climate
 physical weathering
 glacial till
 prairie soil
 glacier
 timber soil
 loess
 topography
 native vegetation
What is soil?
 The top layer of the Earth’s surface, suitable for the
growth of plants.
* Contains both organic and inorganic material
 Soil was formed over many centuries
It is durable and could last as long as our species survives
 So fragile it can be destroyed overnight
 Cannot be replaced once it is destroyed.

Importance of Soil
 Why is the management of our soil so important?
It is the backbone of life.
 It supports plant growth.
 It catches and stores our water.
 It supports buildings and structures.
 If mismanaged it can be destroyed very quickly.

What are five different factors that affect soil
formation?
 I. Five primary
factors affect the
process of soil
formation and
development.
What are five different factors that affect soil
formation?
 A. Parent material—the type of rock material from
which the soil is formed
 B. Topography—the slope characteristics of the soil
 C. Living organisms—the organisms, including plant
material, that live within the soil
What are five different factors that affect soil
formation?
 D. Time or weathering—the age of the
soil or the climate where the soil is
found
 E. Climate—the temperature and
moisture characteristics of the area
where the soil was formed
What are some different types of parent material
that affect soils?
 II. Parent material is formed by the disintegration
and decomposition of rock. It is classified according
to the way it was moved and scattered.
What are some different types of parent material
that affect soils?
 A. Most soils in Illinois have been formed from material
originally moved by glaciers. A glacier is a large, longlasting river of ice that is formed on land and moves in
response to gravity. Two major glaciers, the Illinoisan
and the Wisconsinan, had the greatest influence on
present-day soils in Illinois. The Illinoisan glacier
originated thousands of years before the Wisconsinan
glacier and covered nearly the entire state. Later, the
Wisconsinan glacier covered slightly more than the
northeastern third of Illinois. Soils in southern Illinois
are much older and less productive than those in
northern Illinois. Soils of glacial origin are classified as
loess, outwash, or glacial till.
What are some different types of parent
material that affect soils?
 1. About 64 percent of the soil in Illinois has been
formed from loess. Loess has developed some of the
best soil in the state. Loess originated from the
blowing of the soil after the glaciers melted and
dried. It is the single most desirable soil parent
material. This is due to its well-balanced mineral
content, medium texture, and excellent waterholding capacity.
What are some different types of parent
material that affect soils?
 2. About 16 percent of the soil in Illinois has been
formed from outwash. This type of soil is most
extensive in northern Illinois. Outwash originated
when the glaciers melted. The melted waters carried
the gravelly materials away to be deposited below the
glacial ridges. Sandy outwash was carried farther
downstream, and the finer materials—silt and clay—
were deposited in lakebeds or slow-moving streams.
What are some different types of parent
material that affect soils?
 3. About 11 percent of the soil in Illinois is from
glacial till. It is found primarily in northeastern
Illinois. Glacial till is parent material that was
physically moved and deposited by the glacier itself.
It often contains a variety of sizes of soil particles
that have not been layered from the effects of wind
or water, as have the other two types of glacial soils.
Pebbles and various sizes of boulders are common in
till.
What are some different types of parent
material that affect soils?
 B. About 7 percent of the soil in Illinois is a result of
recent sediments deposited by streams as they flood.
It is referred to as alluvium. Alluvium is generally a
water-borne material deposited on bottomlands.
What are some different types of parent
material that affect soils?
 C. Bedrock is solid rock usually under the soil or
other loose material. Most of the shale, sandstone, or
limestone bedrock in Illinois is buried by loess,
outwash, glacial till, or alluvium. However, in the
unglaciated areas of northwestern and extreme
southern Illinois, weathered bedrock has provided
soil parent material. About 2 percent of the soil in
Illinois can be attributed to bedrock or thinly covered
bedrock.
 2. Rocks aggregates of minerals
 (3 groups)
 Igneous – rock formed by cooling of molten materials
and pushed up to the earths surface – lava, magma
 Sedimentary – formed by solidification of sediment
(3/4 of the earths surface is covered by this)
 Metamorphic- igneous or sedimentary rocks that have
been reformed because of great heat or pressure
 Marine deposits
 Deposits left from ancient ocean floor
 Lacustrine deposits
 Deposits left by lakes
 Colluvial deposits
 Left by gravity
 Organic deposits
 Left in swampy and marshy areas
Peat- contains recognizable plant materials
 Muck- completely decayed so that plant parts are no longer
recognizable

What are some different types of parent
material that affect soils?
 D. Organic matter is decayed or partially decayed
plants and animals, roots, and living organisms. Less
than 1 percent of the soil in Illinois is classified as
organic. Organic soil is found 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 soil are peat and muck. Muck is more
decomposed than peat.
What is topography, and how does it affect the
development of soil?
 III. Topography is 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. The amount of moisture
in the soil during its development affects the rate of
weathering and the subsoil colors. Soils in depressions
and on nearly level topography are likely to have poor or
very poor natural drainage. Soils on moderately sloping
to steep topography are usually well drained.
Topography
 Lay of the land
 Items in topography
include
Slope
 Drainage
 Plants around

 Slope and drainage affect soil formation both directly
and indirectly.
 Steep slopes cause soil runoff of water.
 Breaks up soil.
 Adds deposits to lower levels
 Exposes lower layer of soil (subsoil).
 Percolation – process in which water passes
through the soil.
Soils on level land = poor drainage
 Soils on sloped land = better drainage

 Drainage affects water table
 When soil is saturated little or no air can penetrate.
 Lack of air reduces action of microbes and other soil forming
activities.
 Poor air and water movement causes marbling.

Marbling – discoloration of the soil.
 Poor drainage and excessive water retards plant
growth.
 Drainage affects water table
 When soil is saturated little or no air can penetrate.
 Lack of air reduces action of microbes and other soil forming
activities.
 Poor air and water movement causes marbling.

Marbling – discoloration of the soil.
 Poor drainage and excessive water retards plant
growth.
Slope
 Amount of rise and fall
of the land in a set 100
feet.
 Rise/Run
 Given as a percentage.
 There is a 12 foot rise in
75 feet.
 12/75 = 16% slope
How do living organisms affect the development
of soil?
 IV. Organisms that live in soil—
plants, animals, and microbes—
actively affect soil formation.
How do living organisms affect the development
of soil?
 A. The greatest effect on the development of soil is
from plants that once grew in it. These plants are
referred to as native vegetation. Native vegetation
determines the kind and amount of organic matter in
the soil. In Illinois, there are two primary types of
native vegetation: tall prairie grass and deciduoushardwood forests. Soils in the areas of this vegetation
are called prairie soil and timber soil.
How do living organisms affect the development
of soil?
 1. Prairie soil has 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 gave the soil high organic-matter
content.
 2. Timber soil tends 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.
How do living organisms affect the development
of soil?
 B. 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 that
incorporate organic matter into the soil are
examples.
Living Organisms
 Causes the decay of organic material
 Microbes are microscopic plants and animals, which
help in the decaying process.

Release CO2 and other essential compounds
 Insects, worms, and help in this process by mixing
the various soil materials.
What is weathering? How does weathering and
time affect soil?
 V. Weathering plays a
major role in the formation
of soil. Weathering is the
decomposition of rocks.
What is weathering? How does weathering and
time affect soil?
 A. There are two types of weathering:
 1. Physical weathering—the effects of climatic
factors, such as temperature, water, and wind. Freezing
and thawing is a major contributor to physical
weathering.
 2. Chemical weathering—the effects of factors that
change the elemental makeup of rock and break 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.
What is weathering? How does weathering and
time affect soil?
 B. Weathering causes soil to develop, mature, and age.
 1. Develop—Soil develops rapidly. Plant nutrients are
released, and organic matter accumulates. Soils will
develop faster in humid regions than in arid regions.
 2. Mature—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.
 3. Age—Minerals continue to break down, and clay is
leached into the subsoil. The soil becomes lighter in color
from less organic matter.
How does climate affect soil development?
 VI. Elements of climate influence
soil formation. Climate is the
weather in a region over a long
period. Three elements of climate
related to soil development are
temperature, rainfall, and wind.
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.
Climate and Location
 Greatly affects the rate of weathering by the
temperature.
The warmer the temperature the more organisms there are.
 This increases the chemical reaction time in breaking down
materials.

 Slope and location of a field also affect erosion and
drainage.
 High Temperatures along with tree cover and
moisture on leaf residue = acidic soils
How does climate affect soil development?
 A. The climate in Illinois is said to
be of the continental type. It is
characterized by hot summers and
cold winters. This climate
enhances the weathering process
through freezing and thawing.
How does climate affect soil development?
 B. Rainfall during the growing season is similar
across the state; however, southern Illinois receives
more rainfall during the winter and early spring.
Soils in humid regions are subject to more leaching
than soils in dry regions. Rainfall wears the rock
away a little at a time.
 Areas of High rainfall are usually leached and
somewhat acidic.

Leaching – process in which contents are removed from
the soil
 To much water prevents or describes microbial
growth and may exclude air by water logging.
 Water and temperature have the effect of swelling
and contracting of soil particles.
How does climate affect soil development?
 C. Wind also wears the rock away. Particles carried
by the wind strike the rock and wear it down.
REVIEW
 1. What are five different factors that affect soil formation?
 2. What are some different types of parent material that affect
soils?
 3. What are some different types of parent material that affect
soils?
 4. What is topography, and how does it affect the development
of soil?
 5. How do living organisms affect the development of soil?
 6. How does climate affect soil development?