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 reducessoil fertility, pollutes streams, and requiresexpensive 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 ofthe building process involves shifting of largeportions of the Earth’s surface known asplates.


• The Earth is composed of an outer crust, athick layer of plastic mantle, and a centralcore.

• Crust: is an extremely thin, less dense, solid coveringover the underlying mantle.

• Mantle: makes up majority of earth, surrounds coreof iron, inner portion is solid and outer portioncapable flow.



Plate tectonics: large plate of crust and outermantle (lithosphere) slowly moving over liquidsurface of mantle.

• Heat: from earth core causes movement.

• Plates : are pulling apart in some areas, andcolliding in others.

• Approximately half of the surface of the Earthhas been formed in this way in the past 200million years.

• The bottom of the Atlantic and Pacific Oceansand the Rift Valley and Red Sea area of Africaare 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 sizeand 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; releaseschemicals (acid) causing further fragmentation andchemical breakdown of the rock particles ; contributes toone of the soil components (such as humus) through their death and decay.


Human < a kind of organic material resulting from thedecay of plant and animal remains.

It is a very important soil component that accumulateson the surface and ultimately becomes the componentmixed with the top layers of rock particles, and suppliessome 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 togetherand helps to create crumbly soil which allows waterabsorption 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 drainageare also improved.

• Plant roots :release of organic matter and nutrients intosoil and provide channels for water and air.

• Bacteria and Fungi :act as decomposers to break downorganic material ; serve as important links in many mineralcycles ; release nutrients.

• Soil pH: affects the availability of nutrients—affects thekinds of plants that will grow — affects the amount oforganic matter added to soil.

• The amount of rainfall: affects the amount ofcalcium, magnesium and potassium are leached fromthe 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. Thetexture is gritty and retains water very easily, yet thedrainage is good.

Peaty Soil

This kind of soil is basically formed by the accumulationof dead and decayed organic matter, it naturally containsmuch more organic matter than most of the soils. It isgenerally found in marshy areas. The decomposition ofthe organic matter in this soil is blocked by the acidity ofthe soil. This kind of soil is formed in wet climate.

Chalky Soil

Unlike peaty soil, chalky soil is very alkaline in natureand consists of a large number of stones. The fertilityof this kind of soil depends on the depth of the soil that is on the bed of chalk.

d Its Uses18/09/14 Environmental Science-Soil an 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 Science-Soil and Its Uses18/09/14 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 Science-Soil and Its Uses 21 5


SOIL PROFILE

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).

A Horizon - (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.

A Horizon 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 Erosionwhat 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 fluvialsystems, typically on large timescales. Streambank erosion canalso be induced or exaggeratedby 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 AgricultureCountry 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 1.7Eur1o8p/0e9/14 Environmental Sc2ie9n.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.

This land is no longer productive farmlandsince erosion has removed the topsoil.


This rolling farmland shows strip contourfarming to minimize soil erosion by runningwater. It should continue indefinitely to beproductive farmland.

Poor and Proper Soil ConservationPractice

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 conservationtillage 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.