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Option Unit Geo Ecology

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Option Unit Geo Ecology Soils Learning Objectives Describe what soil is made of (soil composition) Explain how soil is formed. Describe a typical soil profile. – PowerPoint PPT presentation

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Title: Option Unit Geo Ecology


1
Option Unit Geo Ecology
  • Soils

2
Learning Objectives
  1. Describe what soil is made of (soil composition)
  2. Explain how soil is formed.
  3. Describe a typical soil profile.
  4. Name and describe the main characteristics of
    soil.
  5. Name and explain processes that affect soil
    formation.
  6. Describe the factors affecting soil formation.
  7. Explain how these factors and processes
    influcence soil characteristics.

3
  • Soil composition
  • (what soil is made of)

4
Soil Composition
  • MINERAL MATTER (45)
  • ROCK PARTICLES FOUND ON THE BEDROCK AND WEATHERED
  • ROCK
  • AIR (25)
  • FOUND IN THE PORE SPACES BETWEEN THE ROCK GRAINS.
  • WATER (25)
  • ALSO FOUND IN PORE SPACES. IN DRY WEATHER, WATER
  • FORMS A THIN FILM AROUND THE GRAINS. IN WET
    WEATHER, IT
  • FILLS THE PORES.
  • HUMUS (4)
  • PRODUCED FROM DECAYING VEGETATION SUCH AS LEAVES
  • AND THE REMAINS OF DEAD ANIMALS.
  • LIVING ORGANISMS (1)
  • EARTHWORMS, BEETLES, FUNGI, BACTERIA

5
How Is Soil Formed?
  • STEP ONE
  • Solid rock particles are broken down by
    mechanical weathering. This forms small soil
    grains
  • STEP TWO
  • Chemical weathering releases important
    nutrients from the rock e.g. calcium, potassium

6
  • STEP THREE
  • Seeds are blown or carried onto the soil
    grains and may grow into plants that enrich the
    soil when they die. Eg mosses and lichens
  • STEP FOUR
  • Micro- organisms break down the remains of
    plants and form humus. This helps bind the soil
    together and improve fertility of soil.
  • STEP FIVE
  • The cycle continues until the soil reaches max
    fertility.

7
Soil Profile
8
(No Transcript)
9
Soil Profile
A HORIZON Topsoil. Dark Coloured.
O ORGANIC HORIZON. Leaves, dead animals, dead
plants. Humus is formed as the dead organic
matter begins to decay.
B HORIZON Zone of mineral accumulation where
rainwater percolates through the soil.
C HORIZON
10
Soil Characteristics
  • 6 Soil Characteristics
  • Colour
  • Structure how the soil grains are stuck
    together
  • Texture how the soil feels to touch
  • Humus
  • Soil PH
  • Water Content

11
Soil Characteristics
  • COLOUR
  • SOILS HAVE A RANGE OF COLOURS.
  • EG PEAT IS DARK BLACK, OTHER SOIL
  • MAY BE BRIGHT RED OR YELLOW.
  • THE COLOUR OF A SOIL DEPENDS ON
  • ITS PARENT MATERIAL OR ON THE
  • PROCESSES THAT HAVE OCCURRED
  • SUCH AS LEACHING.

12
Soil Characteristcs
  • 2. STRUCTURE
  • THIS DESCRIBES THE WAY IN WHICH SOIL GRAINS ARE
    LUMPED TOGETHER BY HUMUS AND CLAY PARTICLES.
  • IF YOU PULL A PLANT AWAY FROM THE GROUND, ITS
    ROOTS WILL HOLD ONTO THE SOIL GRAINS. LOOK
    CLOSELY AND YOU WILL SEE THAT THE GRAINS ARE IN
    SMALL LUMPS KNOWN AS PEDS.
  • THE SHAPE OF THESE PEDS INDICATES THE STRUCTURE
    OF THE SOIL.
  • THE SPACES BETWEEN THE PEDS HOLD AIR AND WATER
    AND ARE IMPORTANT FOR PLANTS TO ACCESS AIR AND
    WATER IN SOIL.
  • OVERCROPPING AND OVERGRAZING DAMAGE THE STRUCTURE
    OF THE SOIL, REDUCING ITS ABILITY TO SUPPORT
    PLANT GROWTH.

13
  • Crumb small rounded clumps similar to
    breadcrumbs in
  • size. Loam soils have this structure and it is
    very good for
  • holding air and water. It is well drained and
    plants grow
  • well.
  • Blocky Structure peds are closely packed
    angular
  • blocks. Well drained but can be compacted easily
    and
  • plants have difficulty growing in it when this
    occurs. Sandy
  • soils have this structure.
  • Platy Structure peds are arranged in thin
    layers. Forms
  • in clay soils and is poorly drained. Plants have
    difficulty
  • growing in soils with this structure.

14
Soil Characteristics
  • 3. TEXTURE
  • http//www.youtube.com/watch?vob2AMqZMLiw
  • CONTROLLED BY THE AMOUNT OF SAND, SILT, AND CLAY
    PARTICLES IN THE SOIL.
  • DIFFERENT SOILS HAVE DIFFERNET AMOUNTS OF PORE
    SPACE WHICH AFFECTS HOW MUCH AIR CAN BE HELD
    BETWEEN PARTICLES AND ALSO THE WATER CONTENT AND
    DRAINAGE CAPACITY OF THE SOIL.

15
Texture
  • THERE ARE THREE MAIN TEXTURES
  • CLAY (PARTICLE DIAMETER 0.0002mm NOT VISIBLE
  • TO NAKED EYE)
  • SILT (PARTICLE DIAMETER BETWEEN 0.0002 AND
  • 0.05mm BARELY VISIBLE TO NAKED EYE)
  • SAND (PARTICLE DIAMETER 0.05mm TO 2mm
  • VISIBLE TO NAKED EYE).
  • WHEN DESCRIBING SOIL TEXTURES, THE TERMS SILT,
    CLAY AND SAND ARE IMPORTANT BECAUSE THEY INDICATE
    THE SIZE OF THE GRAINS IN THE SOIL.

16
  • CLAY SOILS
  • SMALLEST SIZED PARTICLES.
  • STICKY SOIL WHEN WET.
  • CONTAIN APPROX 0-45 SAND, 0-40 SILT AND
    40-100CLAY.
  • NATUARALLY HIGH IN NUTRIENTS SO PLANTS GROW WELL.
  • OFTEN BAKED DRY IN SUMMER WITH VISIBLE SURFACE
  • CRACKS.
  • OFTEN CONSTANTLY WET AND WATERLOGGED IN WINTER.
  • CAN BE DIFFICULT TO DIG.
  • HOLDS TOGETHER LIKE PLAYDOUGH.

17
  • SILTY SOILS
  • CONTAINS PARTICLES SMALLER THAN SAND BUT
  • LARGER THAN CLAY SOILS.
  • FEELS POWDERY.
  • STICKS TOGETHER WHEN WET BUT OFTEN WILL NOT
  • HOLD ITS SHAPE WHEN DRY.
  • CAN BE BADLY DRAINED.

18
  • SANDY SOILS
  • CONTAINS PARTICLES VISIBLE TO NAKED EYE.
  • FEEL GRITTY TEND NOT TO STICK TOGETHER WHEN
    WET.
  • GENERALLY CONTAIN 85-100SAND,0-15SILT-0-10CLAY.
  • WATERLOGGING RARE AS THEY ARE VERY FREE DRAINING.
  • WATERING AND FEEDING OF PLANTS OFTEN NECESSARY AS
  • NUTRIENTS CAN DRAIN AWAY EASILY.
  • QUICK TO WARM IN SPRING SO PLANTING CAN BE DONE
  • EARLIER IN SANDY SOILS THAN OTHER TYPES.

19
  • LOAM SOILS
  • RARELY COMPOSED OF JUST SAND, SILT OR CLAY-
  • USUALLY MIXTURE OF THE THREE.
  • LOAM CONTAIN ROUGHLY EQUAL AMOUNTS OF
  • EACH.
  • MOST PLANTS WILL GROW IN LOAM SOILS.
  • BROWN AND CRUMBLY IN TEXTURE.
  • RARELY WATERLOGGED IN WINTER OR OVERDRY IN
  • SUMMER.
  • LIGHT AND EASY TO DIG.
  • NATURALLY HIGH IN NUTRIENTS.

20
Soil Characteristics
  • 4. HUMUS CONTENT
  • IMPORTANT DUE TO ITS ABILITY TO SUPPORT PLANT
    GROWTH.
  • SOLS RICH IN HUMUS TEND TO BE DARK IN COLOUR.
    HUMUS IS A DARK BLACK GEL FORMED BY ROTTING
    PLANTS AND VEGETABLE MATERIAL IN SOIL.
  • THIS GEL HELPS TO BIND SOIL GRAINS TOGETHER. AS
    IT IS WASHED INTO THE GROUND BY RAIN, IT ADDS
    NUTRIENTS TO THE SOIL. LIVING THINGS ALSO ADD
    HUMUS TO SOIL BY EXCRETION.
  • EARTHWORMS, BEETLES AND LARVAE BURROW THROUGH
    SOIL AND CREATE AIR SPACES FOR PLANT ROOTS.
  • WHEN THESE CREATURES DIE, THEIR BODIES DECOMPOSE
    AND FURTHER ENHANCE THE NUTRIENT QUANTITY IN THE
    HUMUS.

21
Soil Characteristics
  • 5. ACIDITY/ALKALINITY OF THE SOIL
  • THE PH OF THE SOIL IS HOW ACIDIC OR ALKALINE IT
    IS (LITMUS TEST JC SCIENCE). MOST PLANTS PREFER
    A SLIGHTLY ACIDIC SOIL WITH A PH OF 6.5
  • PEAT SOILS ARE EXTREMELY ACIDIC AND CONTAIN FEW
    LIVING PLANTS.
  • NEUTRAL SOILS ARE MOST SUITED TO BACTERIA WHICH
    HELP IN TURN TO RELEASE NUTRIENTS SUCH AS
    NITROGEN INTO THE SOIL.

22
Soil Characteristics
  • 6. WATER CONTENT/ RETENTION
  • THE AMOUNT OF WATER A SOIL CAN HOLD DEPENDS ON
    THE HUMUS CONTENT, TEXTURE AND STRUCTURE.
  • SOILS RICH IN HUMUS CAN HOLD MORE MOISTURE THAN
    THOSE WHICH LACK HUMUS.
  • SOILS THAT HAVE A SANDY TEXTURE, ARE OFTEN DRY
    BECAUSE WATER DRAINS BETWEEN THE SAND GRAINS VERY
    QUICKLY.
  • A CLAY SOIL TENDS TO HOLD MORE WATER DUE TO THE
    VERY SMALL GRAINS WHICH HAVE LARGE SURFACE AREAS
    AND THEREFORE MORE WATER AROUND THEM.

23
Processes affecting soil characteristics You
know some of these already.. Think!!
24
Processes
  • Weathering
  • Humification
  • Leaching
  • Podzolisation
  • Gleying
  • Laterisation
  • Salinisation
  • Calcification
  • The factors of climate, relief, rock type, living
    things and
  • time all influence which one of these processes
    take place.

25
Weathering
  • Physical and chemical breakdown of rocks
  • into smaller pieces. Soil grains can be
  • released from rocks by weathering.
  • The soil grains produced by weathering
  • keep the characteristics of the parent rock
  • such as PH, texture and colour.
  • Carbonation and oxidation can release nutrients
  • such as phosphorous, calcium and iron from the
  • mineral grains.

26
Humification
  • Dead organic matter is converted into humus by
    fungi and bacteria. Makes the soil fertile as it
    releases nutrients into the soil.
  • Rain washes the humus into the soil.
  • Climate is an important factor affecting the rate
    of humification. Hot humid climates
    humification is very fast. The lack of water in
    deserts may limit the amount of humus that can be
    washed into the soil. In Ireland humification
    occurs more slowly in Winter and in cold artic
    climates humification may stop.

27
Leaching
  • The removal of nutrients from the soil by water.
  • Sometimes minerals build up in a layer lower down
    in the soil (hardpan)
  • A certain amount of leaching is needed to wash
    humus into soil. However excessive leaching makes
    the soil infertile.

28
Podzolisation
  • Type of leaching that occurs where rainwater is
    more acidic.
  • Podzol soils foirm under coniferous forests as
    these forests decompose they add to the acidity
    of the rainwater.
  • The water seeping through the soil beneath this
    dead vegetation becomes acidic due to the
    absorption of humic acids from rotten vegetation.
  • The top layer of podzolised soils is ash grey in
    colour. The layer below is enriched with the
    dissolved mineral from above and is darker in
    appearance.
  • Podzols may also contain a layer of reddish iron
    oxide in the B horizon. This is called a hard pan
    or iron pan and prevent water from draining
    through the soil.

29
Gleying
  • Process when the soil is waterlogged and lacks
    oxygen.
  • Water is between the soil peds and prevents
    living things from surviving. They lack organic
    matter.
  • Climate and relief can lead the gleying. Heavy
    rain can cause the land to become waterlogged. If
    the land dips and hollows water can collect in
    the hollows
  • Gley soils have patches of grey/blue colouration.
  • Common in Irelands drumlin belt (Co. Cavan, Co.
    Monaghan).

30
Laterisation
  • Type of severe chemical weathering that occurs in
    tropical and equatorial regions.
  • In areas of heavy rainfall such as the tropics
    and equatorial regions all alkaline material is
    taken from the soil by carbonation. The PH of the
    soil is slightly acidic.
  • The oxidation of iron and alluminium gives the
    soils a red appearance and they are known as
    latosols. If the soil dries out it is turned into
    a hard laterite.

31
Salinisation
  • Occurs when mineral salts move up through the
    soil towards the surface.
  • Can happen in hot desert areas of the world where
    percipitation is low. The amount of water
    evaporating out of the soil is greater than
    percipitation falling.
  • Evaporation causes salts in ground water to rise
    through the soil and collect in the upper layers.
    Salt is deposited on the surface as a hard white
    crust. If salt concentration is too high plants
    are poisoned and die.

32
Calcification
  • Process by which calcium carbonate is
    concentrated near the surface of the soil.
  • Occurs in regions of low rainfall.
  • The amount of water drawn up through the soil by
    plants may be greater than the percipitaiton
    falling on the soil. As a result calcium
    carbonate builds up in the upper layer of the
    soil.
  • Calcium carbonate is a useful substance for
    plants.

33
Factors Affecting Soil Processes and Soil
Characteristics
  • Climate most important factor in soil formation
  • Relief Can influence the dept and drainage of a
    soil
  • Parent Material The type of rock that a soil
    develops from can influence PH, colour,water
    content and texture of soil.
  • Living Things Influence soil fertility
  • Time The longer the soil forming process the
    more developed the soil will become.

34
Activity
  • Read the handout to discover how the above
    factors affect the formation of soil. They do by
    influencing the processes
  • (weathering, leaching etc) and characteristics
    ( colour, PH, etc)

35
Soil Classification
  • 3 Main Groups

36
ZONAL SOILS
  • These form where the influence of climate and
    biological activity have been stable for along
    time.
  • These soils often have distinctive profiles and
    clear horizons. They would include
  • Brown Earths  brown in colour crumb structure
    high natural fertility/ no distinct horizons.
    Found in many parts of Ireland.
  • Podzols Associated with leaching poorly drained
    soil two distinct horizons (ash-grey and reddish
    brown) need addition of fertilizers. Found in
    Cork, Kerry, Wicklow, Mayo and Donegal.

37
INTRAZONAL SOILS
  • These soils form where some local factor such as
    parent material (e.g. presence of limestone) or
    drainage conditions predominate. They would
    include Gley and Peat soils.

38
GLEYS
  • Gleys These are soils that are often waterlogged
    due to impermeable underlying rock. The
    waterlogged condition stopped the breaking down
    of organic matter. These soils are blue/grey in
    colour of poor fertility mainly suited to
    pastoral farming.
  • Found in e.g. north west Munster and in the
    Drumlin Belt of Cavan/Monaghan.

39
PEAT SOILS
  • Peat Soils Black in colour and consist of
    partially decomposed vegetative matter. Heavily
    leached and low in fertility.
  • Blanket peat is found in the uplands, especially
    on acid underlying rock such as the granite of
    the Wicklow Mountains. Raised peat found in
    waterlogged areas of the Central Plain.

40
AZONAL SOILS
  • Azonal Soils - These are immature soils where the
    soil farming processes have not had sufficient
    time to complete their task. These soils do not
    have a well developed profile.
  • They would include Lithosols. Associated with
    recently weathered bed rock where mass movement
    and erosion prevent the development of a soil
    profile. Infertile, used possibly for forestry
    some areas of Connemara

41
What to Know.
  • Should be aware of the different soil types in
    each group.
  • Should describe one Irish soil in detail Brown
    Earth soil.
  • Should describe the aridsols of desert climates
    (we did this when studying the desert biome!)
  • Via syllabus you should be able to compare two
    soil types

42
Irish Brown Earth Soils
  • Read the handout on brown earth soils.
  • It is broken up into the factors that affect its
  • formation and the characteristics of brown
  • earth soils and the processes affecting the
  • formation of brown earth soils

43
  • Human Interaction Question

44
Soil Erosion and Conservation
  • Learning Objectives
  • Name and explain the causes of soil erosion.
  • Describe in detail how human activities can cause
    soil erosion.
  • Name and explain the primary methods of soil
    conservation.

45
Soil Erosion
  • Most soil erosion is caused by natural
  • processes such as flowing water and by
  • wind. Human activities such as overcropping
  • and overgrazing land and deforestation also
  • cause soil erosion.

46
Natural cause of soil erosion
  • Soil erosion by rain
  • Raindrops on average fall at a speed of
  • 32.19km/hr. The force of impact of raindrops
    break
  • apart the soil grains. During heavy rain water
    can
  • no longer seep into the soil and begins to flow
    over
  • the surface (runoff). The water makes channels
  • called rills and gullies in the soil. Millions of
    tonnes
  • of soil are removed from farmland by rainwater in
  • this way.

47
  • Soil erosion by wind
  • Wind is effective at blowing dry exposed soil
  • away. Wind removes soil by
  • Saltation fine and medium sand sized particles
    are lifted a short distance into the air
  • Suspension very fine soil particles are lifted
    from the surface, carried high into the air, it
    remains suspended in the air for long periods.
  • Surface Creep the movement of large soil
    particles along the surface of the soil.

48
  • The amount of soil erosion by wind and rain
  • that occurs depends on
  • The quantity of water moving downhill
  • The speed of the water
  • The strength of the wind
  • The steepness of slope.
  • The condition of the soil surface and the type of
    soil.

49
Human causes of soil erosion
  • Can trigger soil erosion due to poor farming
    methods and deforestation.
  • Farming and deforestation can change soil
    characteristics and damage soil structure.
  • Human activities such as overgrazing,
    overcropping and deforestation have led to
    desertification, soil erosion and famine.
  • Tourism, outdoor activities such as quad biking
    damage fragile soil structure.
  • The amount of soil erosion caused by human
    activities depends on
  • The type of cultivation may leave soil exposed
    to the wind
  • The amount of vegetation cover removed
    deforestation can lead to landslides.
  • The intensity of land use heavily used soils
    are more easily eroded.
  • The length of time land left rested overused
    soils are often dry.

50
Problems caused by soil erosion
  1. Loss of valuable topsoil
  2. Poor soil washed downhill can bury valuable
    fertile soil on the lowland below.
  3. Damage to fields because gully erosion reduces
    the field size and takes land out of production.
  4. Erosion causes a steady but slow plant
    productivity decline.
  5. Desertification

51
Case Study
  • Soil erosion and desertification in the Sahel
    region in Africa.
  • Read the photocopied handout on the above case
    study.
  • Human interaction answer

52
Methods for soil conservation
  • Windbreaks
  • Barriers formed by trees and other plants with
  • many leaves. They are planted around the edges
  • of fields. They stop the wind from blowing soil
  • away and from destroying or damaging crops.
  • They work best when they allow a little wind to
  • pass through to avoid violent gusts of wind
    forming
  • close to the ground that would carry away soil.

53
  • 2. Contour ploughing/ strip ploughing
  • The tractor operator follows the contours of
  • a hillside. They go around the sides of hills.
  • The plough creates mini terraces, slowing
  • or stopping the flow of rainwater and
  • encouraging it to seep into the soil.
  • If ploughing straight up and down the terrace
  • would create ditches allowing water to flow
  • down picking up speed and soil.

54
  • 3. Stubble planting
  • The old stubble of harvested crops is not
    ploughed
  • back into the soil. Any fertilisers and new seed
  • planted afterwards are inserted into the soil
  • through small slits cut into the soil. Ie the
    soil is left
  • undisturbed.
  • The stubble will reduce wind and water erosion
  • while the new crop is growing. The stubble left
    in
  • the soil will rot into it eventually.

55
  • 4. Terraces
  • Large steps cut into a hillside to make flat land
    for
  • agriculture. Work by reducing slope length and
    steepness
  • so water looses energy (cant carry soil away as
    fast).
  • 5. Stone walls or bunds
  • These low walls are placed along the contour of a
  • hill and capture water allowing it to filter into
    the
  • soil rather than running off downhill.
  • 6. Reduce ploughing in dry/windy weather
  • Reduces the risk of wind erosion. Soil is lost
    during the
  • plouging process. If the following days are windy
    more soil
  • will be lost. Rain is needed to dampen and settle
    the fine
  • soil particles.

56
Exam Questions
  • Remember the marking scheme
  • 3 or 4 paragraphs in each answer
  • Coherance marks for each paragraph.
  • You will have to adjust your notes to suit the
  • question you are asked.

57
  • Explain how weathering, leaching and
    podzolisation have impacted on the
  • characteristics of soil.
  • Soil characteristics are affected by their
    immediate environment and by
  • combination of processes operating in that
    environment.
  • Examine any three soil processes that affect soil
    characteristics.
  • Examine two of the natural processes which
    influence soil formation.
  • Discuss how human activities can accelerate soil
    erosion.
  • Examine two ways in which human activities have
    impacted on soils.
  • Examine how over-cropping / over-grazing and
    desertification can affect soils.
  • Describe and explain the characteristics of any
    one soil type studied by you.
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