Soil and its uses Group 5

18/09/14 Environmental Science-Soil and Its Uses 1

Objectives
Describe the geologic processes that build and
erode the Earth’s surface.
List the physical, chemical, and biological factors
involved in soil formation.
Explain the importance of humus to soil fertility.
Differentiate between soil texture and soil
structure.
Explain the role of living organisms in soil
formation and fertility.
Describe the various layers in a soil profile.

Describe the processes of soil erosion by
water and wind.
Explain how contour farming, strip farming,
terracing, waterways, windbreaks, and
conservation tillage reduce soil erosion.
Understand that the misuse of soil reduces
soil fertility, pollutes streams, and requires
expensive remedial measures.
Explain how land not suited for cultivation
may still be productively used for other
purposes.

• There are forces that tear it down. Much of
the building process involves shifting of large
portions of the Earth’s surface known as
plates.
• The Earth is composed of an outer crust, a
thick layer of plastic mantle, and a central
core.
• Crust: is an extremely thin, less dense, solid covering
over the underlying mantle.
• Mantle: makes up majority of earth, surrounds core
of iron, inner portion is solid and outer portion
capable flow.

Plate tectonics: large plate of crust and outer
mantle (lithosphere) slowly moving over liquid
surface of mantle.
• Heat: from earth core causes movement.
• Plates : are pulling apart in some areas, and
colliding in others.
• Approximately half of the surface of the Earth
has been formed in this way in the past 200
million years.
• The bottom of the Atlantic and Pacific Oceans
and the Rift Valley and Red Sea area of Africa
are areas where this is occurring.

Weathering: Factors bring about fragmentation
or chemical change of parent material.
Mechanical: Result from physical forces reducing
size of rock particles.
Temperature changes and abrasions are primary
agents.
Chemical weathering: Rock fragments exposed
to atmosphere may oxidize, or otherwise
chemically change.
Others: temperature changes, freezing of water
& thawing and actions of plants or animals.

Physical Fragmentation by Freezing and Thawing

• Land is a part of the world not covered by the
oceans.
• Soil is a thin covering over the land consisting of
a mixture of minerals, organic material, living
organisms, air, and water that together support
of the growth of plant life.
Role of organisms in soil development is very
important

The Components of Soil

Soil formation – a combination of physical,
chemical and biological process over time.
the soil building begins with the
fragmentation of the parent material
Parent material - ancient layers of rock, or
more recent geologic deposits from lava flows
or glacial activity.

Factor affecting soil formation < the kind and
amount of soil developed depends on the
following factors:
1. the kind of parent material present (such as the size
and chemical nature of the particle).
2. the climate (such as temperature) and time involved.
3. the slope of the land.
4.the role of the organisms: traps small particles; releases
chemicals (acid) causing further fragmentation and
chemical breakdown of the rock particles ; contributes to
one of the soil components (such as humus
) through their death and decay.

Human < a kind of organic material resulting from the
decay of plant and animal remains.
 It is a very important soil component that accumulates
on the surface and ultimately becomes the component
mixed with the top layers of rock particles, and supplies
some of the needed nutrients to plants.
 Humus increase the water-holding capacity of soil.
 Humus increase the acidity of soil so that the inorganic
nutrients become available to plants.
 Humus also tends to stick other soil particle together
and helps to create crumbly soil which allows water
absorption and permits air to be incorporated into soil
(this helps the soils have more pore space).

Other Factors Influencing Soil Formation
•Burrowing animals (Earthworms): resulting further mixing of
organic and inorganic material, which increases the amount of
nutrients available for plant use; soil aeration and drainage
are also improved.
• Plant roots :release of organic matter and nutrients into
soil and provide channels for water and air.
• Bacteria and Fungi :act as decomposers to break down
organic material ; serve as important links in many mineral
cycles ; release nutrients.
• Soil pH: affects the availability of nutrients—affects the
kinds of plants that will grow — affects the amount of
organic matter added to soil.
• The amount of rainfall: affects the amount of
calcium, magnesiumand potassiumare leached from
the soil.

Soil Types
 This soil type has the biggest particles; and the
bigger size of the particles in a soil the better
is aeration and drainage of the soil. This soil is
granular and consists of rock and mineral
particles that are very small.
 To check if soil is sandy, moisten a small
sample of soil and try to make a ball using
your palms. If the soil is sandy, then no dirt
balls will form and the soil will crumble and
fall through the fingers.

Silty Soil
 Silty soil is considered to be one of the most
fertile of soils. It can occur in nature as soil or as
suspended sediment in water column of a water
body on the surface of the earth. It is composed
of minerals like quartz and fine organic particles.
 To check if the soil you have is silty, take a small
amount of moist soil and rub it between your
fingers. If the soil is silty soil, it will feel slick and
stick to your fingers.

Clay Soil
 Clay is a kind of material that occurs naturally
and consists of very fine grain material with very
less air spaces. Due to this it is difficult to work
with this soil, because the drainage in this soil is
low.
 To identify if the soil is clay soil, take a soil
sample and damp it with water. Feel it between
your palms. You will find clay soil is sticky and
retains a good amount of water.

Loamy Soil
 This soil consists of sand, silt and clay to some extent. It
is considered to be the perfect soil for gardening. The
texture is gritty and retains water very easily, yet the
drainage is good.
Peaty Soil
 This kind of soil is basically formed by the accumulation
of dead and decayed organic matter, it naturally contains
much more organic matter than most of the soils. It is
generally found in marshy areas. The decomposition of
the organic matter in this soil is blocked by the acidity of
the soil. This kind of soil is formed in wet climate.

Chalky Soil
 Unlike peaty soil, chalky soil is very alkaline in nature
and consists of a large number of stones. The fertility
of this kind of soil depends on the depth of the soil
that is on the bed of chalk.
18/09/14 Environmental Science-Soil an d Its Uses 22

• Texture < Determined by the size of mineral
particles within the soil.
– Too many large particles leads to extreme leaching as sand
and gravel.
– Too many small particles leads to poor drainage as clay.
Pore Spaces and Particle Size
Environmental 18/09/14 Science-Soil and Its Uses 23

• Structure < Refers to the way various soil
particles clump together.
– In good soils 2/3 of the intra-soil spaces contain air
after the excess water has drained.
Friable—Crumbles easily. Sandy soils are very friable,
while clay soils are not.
– Protozoa, nematodes, earthworms, insects, algae,
bacteria, and fungi are typical inhabitants of soil.

8/09/14 Environmental 1 Science-Soil and Its Uses 25

SOILPROFILE
 What is Soil Profile?
 How does soil develop?
 How many layers in a soil profile?

Soil Profile
• Soil formation begins first with the break down of
rock into regolith. Continued weathering, and soil
horizon development process leads to the
development of a soil profile, the vertical display of
soil horizons.
• Soil Profile - A series of horizontal layers of different
chemical composition, physical properties, particle
size, and amount of organic matter.
• Horizon - Each recognizable layer of the profile.

The various layers in a soil profile
 O Horizon - Litter – Undecomposed or partially
decomposed organic material (Oi + Oa).
 AHorizon - (Topsoil) Uppermost layer –
contains most of the soil nutrients and
organic matter (organic matter + mineral matter).
 E Horizon - Formed from leaching darker materials.
– Not formed in all soils.
– Usually very nutrient poor.

• B Horizon - (Subsoil) Underneath
topsoil,
and it contains less organic matter and
fewer organisms, but accumulates
nutrients leached from topsoil. – Poorly
developed in dry areas.
• C Horizon -Weathered parent material –
very little organic material.
• R Horizon - Bedrock

Type of Soils
• Soil types – Over 15,000 separate soil types
have been classified in NorthAmerica, but the
three major classifications are grassland,
forest, and desert.
• Grassland Soils - Usually have a deep A
Horizon – low rainfall limits topsoil leaching.
AHorizon supports most root growth.

• Forest Soils – Topsoil layer is relatively
thin, but topsoil leachate forms a subsoil that
supports substantial root growth. (High
rainfall areas)
Tropical Rainforests
 Two features of great influence:
 High temperatures
 Rapid decomposition – little litter.
 High rainfall
 Excessive leaching of nutrients

• Desert Soils – very poorly developed
horizons (little rainfall).
 Not support a large amount of plant growth
 The soil is exposed
 Little organic matter and little leaching of
materials
Therefore, the soil profile is different with
different type of soil.

Soil Erosion
what is a soil erosion?
Soil Erosion is a natural process and
removal of soil from one location to
another. It becomes a problem when
human activity causes it to occur much
faster than under natural conditions.

Types of soil erosion
 The main forms of soil erosion are:
• surface erosion
• fluvial erosion
• mass-movement erosion
• streambank erosion.

Surface erosion
 When rain, wind or frost detach
soil particles from the surface,
the particles are washed or
blown off the paddock.
Fluvial erosion
 This occurs when running water
gouges shallow channels or
deep gullies into the soil.

Mass-movement erosion
• When gravity combines with
heavy rain or Earthquakes.
Streambank erosion
• Streambank erosion is a natural
process that occurs in all fluvial
systems, typically on large time
scales. Streambank erosion can
also be induced or exaggerated
by man's activities.

CAUSES OF SOIL EROSION
There are two factor:
 Natural factor
*heavy rains on weak soil.
*vegetation depleted by drought: rain drops
are free to hit the soil.
*steep slopes: gravity “pulls harder;” water
flows faster.
* sudden climate change.

Human Factor
* change of land (deforestation)
*intensive farming: to plough
*housing development: soil is bareroad
construction: roads are cut
* road construction: roads are cut
watch video soil erosion!

Soil Erosion

Stopping Soil Erosion
Soil erosion can be stopped in so many ways.
Depending on the environment one of these methods
can be used or all the methods can be used in
combination
* Plant more trees
* Avoid deforestation
* Avoid soil, air pollutants in destruction of plant habitat, etc

Soil Conservation Practice
• The kind of agricultural activities that land can be used for are
determined by soil structure, texture, drainage, fertility,
rockiness, slope of the land, amount and nature of rainfall, and
other climate condition.
• A relatively large proportion, about 20% of U.S. land is suitable
for raising crops. However, only 2% of that land does not
required some form of soil conservation practices. This means
that nearly all of the soil in the U.S. must be managed in some
way to reduce the effects of the soil erosion by wind or water.

The percentage of land suitable for Agriculture
Country Percent Cropland Percent Pasture
World 11.0 26.0
Africa 6.3 28.8
Egypt 2.8 5.0
Ethiopia 12.7 40.7
Kenya 7.9 37.4
South Africa 10.8 66.6
North America 13.0 16.8
Canada 4.9 3.0
United States 19.6 25.0
South America 6.0 28.3
Argentina 9.9 51.9
Venezuela 4.4 20.2
Asia 15.2 25.9
China 10.3 30.6
Japan 12.0 1.7
Eur1o8p/
0e9/14 Environmental Sc2i
e9n.c9e
-Soil and Its Uses 17.1 44

• Contour Farming—Tilling at right angles to the slope of the
land. Each ridge acts as a small dam.
• Strip Farming—Alternating strips of closely sown crops to slow
water flow.
• Terracing—Level areas constructed at right angles to the slope
to retain water.
– Good for very steep land.

• A study of FAO that up to 40% of the world’s
agricultural lands are seriously affected by soil
degradation.
• WRI in 2003 state that land degradation affected
around 70% of world range land, 40% of rain-fed
agricultural land, and 30% of irrigated land.
• According to UNEP, an estimated 500 million
hectares of land in Africa have affected by soil
degradation since 1950, including as much as 65%
of agricultural land.

• Whenever soil is lost by water or wind erosion, the
topsoil, the most productive layer, is the first to be
removed. When the topsoil is lost, the soil’s fertility
decreases, and larger amounts of expensive
fertilizers must be use to restore the fertility that
was lost. [food]
• In addition, the movement of excessive amounts of
soil from farmland into streams has several
undesirable effects.

 A dirty stream is less aesthetically pleasing than a
clear stream.
 Too much sediment in a stream affects the fish
population by reducing visibility, covering spawning
sites, and clogging the gills of the fish.[fishing]
 The soil carried by a river is eventually deposited
somewhere.

 In many cases, this soil must be removed by dredging to
clear shipping channels.
 For all these reasons, proper soil conservation measures
should be employed to minimize the loss of topsoil.
 When the soil is not protected from the effects of running
water, the topsoil is removed and gullies result. This can be
prevented by slowing the flow of water over slopping land.
 By using appropriate soil conservation practices, much of the
land not usable for crops can be used for grazing, wood
production, wildlife production, or scenic and recreational
purposes.

Poor and Proper Soil Conservation
Practice
This land is no longer productive farmland
since erosion has removed the topsoil.
This rolling farmland shows strip contour
farming to minimize soil erosion by running
water. It should continue indefinitely to be
productive farmland.

Summary
1. The surface of the Earth is in constant flux.
2. The movement of tectonic plates result in the formation of
new land as old land is worn down by erosive activity.
3. Soil is an organized mixture of minerals, organic material,
living organisms, air, and water.
4. Soil formation begins with the breakdown of the parent
material by such physical processes as changes in temperature,
freezing water, or wind.
5. Oxidation and hydrolysis can chemically alter the parent
material.
6. Organisms also affect soil building by burrowing into and
mixing the soil, releasing nutrients, and decomposing.
7. Topsoil contains a mixture of humus and inorganic material,
both of which supply soil nutrients.

8. The ability of soil to grow crops is determined by the inorganic
matter, organic matter, water, and air spaces in the soil.
9. The mineral portion of the soil consists of various mixtures of
sand, silt, and clay particles.
10. Soil erosion is the removal and transportation of soil by water or
wind.
11. Proper use of such conservation practices as contour farming,
strip farming, terracing, waterways, windbreaks, and conservation
tillage can reduce soil erosion.
12. Misuse reduces the soil’s fertility and causes air-and water-quality
problems.
13. Land unsuitable for crops may be used for grazing, lumber,
wildlife habitats, or recreation.

Soil and its uses Group 5

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Soil and its uses Group 5 (20)

Recently uploaded (20)

Soil and its uses Group 5