Leaving Certificate Agricultural Science

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Leaving Certificate Agricultural Science
Soil 2 Soil Formation
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Soil Formation

• Soil is formed from the weathering of rocks.
• Weathering the breaking down of parent material
  (rock).
• There are 3 types of weathering
• Physical,
• Chemical
• Biological.

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Physical Weathering

• The natural forces carry this out wind, sun,
  frost, ice. Physical breakdown is caused by the
  Freeze Thaw Action phenomenon.
• Igneous and Metamorphic rock surfaces absorb heat
  energy from the sun and in doing so they expand.
• By night as the temperatures drop these rocks
  contract.
• Hairline cracks develop.
• Rain gets into these cracks and when it freezes,
  it expands up to 9 thus causing the rocks to
  shatter.
• The resulting small particles are called Solum.

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Physical Weathering
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Chemical Weathering

• Acid rain and SO2, CO2, CO, NO3
• Burning fossil fuels e.g. coal, turf, oil, and
  natural gas produces Sulphur dioxide. If it
  combines with water it forms Sulphuric acid
• SO2 H2O ? H2SO4 Sulphuric acid
• CO2 H2O ? H2CO3 Carbonic acid
• NO3 H2O ? H2NO3 Nitric acid

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Chemical Weathering

• Chemical breakdown occurs when soluble components
  in the rock are dissolved by water. (A very
  strong solvent)
• This is further emphasised by various types of
  dissolved acids in rainwater.
• Carbonic acid, Nitric acid and Sulphuric Acid are
  common in rainwater.

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Chemical Weathering
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Biological Weathering

• Early plant life like Lichens can breakdown
  rocks.
• Lichens get minerals from rocks by secreting an
  acidic liquid into the rocks.
• This further breaks down the rocks decays slowly.
• When lichens die they also form the first layer
  of humus (decaying material) that will eventually
  become the soil.
• When the humus becomes a few inches thick, other
  plants (like grasses and mosses) can begin to
  grow on it.
• The roots of these plants then can break the rock
  further.

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Biological Weathering
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Glaciation Glacial deposit

• Glaciation is when snow and ice accumulate in
  mountain river valleys and move slowly downwards
  due to gravity.
• When glaciers reach lowland areas, they join
  together and form larger piedmont glaciers.
• In turn these large piedmont glaciers join
  together to form giant ice sheets.
• These ice sheets can cover thousands of kms and
  are moving constantly.
• Glaciation has occurred in Ireland in the past
  and has contributed to Ireland climate and soil.
• North Europe is said to be in an inter-glacial
  period.

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Glaciation
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Glaciation Glacial deposit

• When glaciers and ice sheets move they scrape all
  soil and loose rock from the surface.
• This material becomes mixed in the lower layers
  of the ice and are deposited as glacial drift a
  goof distance away from its original position.
• This material then serves as parent rock for soil
  formation.
• Irelands soils are said to be young because they
  are only 12,000 years old.

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Peat Soils

• There are 3 types of peats Blanket, Basin and
  Raised peats
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• Blanket Peats
• Found in mountainous areas where high rainfall is
  typical (Wicklow, Clare and Kerry to some
  extent).
• Blanket bogs are so called because they form a
  blanket over a wide area.
• Shallow (1 - 2 meters deep at most).
• They do not have as much potential for
  cultivation by large-scale machinery or for
  farming, mainly because where they are located.
• Soils are wet, acidic and infertile.

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Peat
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• Basin Peats
• Occurs in land with a depression i.e. a hollow
  lake or river.
• Dead remain of plants accumulate at the bottom of
  the lake.
• The build up of the dead vegation cuases the lake
  to close over and become land.
• Occurs in water logged and flooded conditions.
• Drier and of more agricultural use than blanket
  bogs

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• Raised bogs
• Further development of basin bogs.
• They are raised above the level of the
  surrounding ground.

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Formation of the Peat Bogs

• After the Ice Age, glaciers left a vast amount of
  small, shallow lakes around Ireland, these were
  taken over by vegetation (plants like reeds and
  sedges) growing from the shore inwards.
• Decaying organic matter filled the lake to above
  the water level, so it is no longer a lake.
• Trees such as birch and alder and shrubs then
  moved in once all the water had gone.
• The areas are then referred to as carr or fen
  (fenn) woods.

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Formation of the Peat Bogs

• These trees would eventually die as well and
  become part of the decaying mass.
• Organic parent material is formed from half
  decomposed plants under very wet anaerobic soils
  or in lakes these conditions prevent the full
  break down of the plants.
• This is referred to as peat parent material and
  they give rise to peat soils.
• The dominant species at this stage are bog mosses
  (sphagnum mosses).
• These bog mosses can soak up five times their
  weight in water and after thousands of years of
  Irish weather, these mosses were able to build up
  to heights of 10 metres above the once lake
  floor.
• These bogs are called Raised bogs and are typical
  of the midlands.

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