Transcript Soils: The Critical Resource

Higher Geography
Biosphere
Case Studies of
Selected Soils
A Soil
Profile
Introduction
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For higher geography you have to know
about 3 main soil types:
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Podsols
Brown Earth Soils
Gley Soils
Podsols
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Podsols usually have clearly defined
horizons. This is due to a process known
as podsolisation.
This involves the pronounced leaching of
material (iron, aluminium and humus)
from the surface layers to the lower
layers.
Podsols location
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Podsols are found in northern boreal
coniferous forests with associated cold,
wet climates in which precipitation
exceeds evaporation.
Podsols are also found in upland
moorland areas.
Podsols Profile (1)
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The Ao horizon forms from decaying plant litter
which can be:
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The pine needles, cones and twigs from coniferous trees.
Dead heather shoots from upland moorland.
Thanks to the cold climate, the organic matter decays
very slowly to form an acidic mor humus.
Rain and melting snow combine with these organic
acids and wash out (eluviate) the minerals from the A
horizon. This produces an ash-coloured, bleached A
horizon.
Podsols Profile (2)
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Lower down the profile, aluminium, iron, clay
and humus are washed in (illuviated) and
redeposited in the subsoil or B horizon.
If iron accumulates over a long enough period,
a rust coloured iron pan can form, often up to
several cm thick.
Iron pans can prevent the penetration of
plant roots and the free drainage of the
podsol resulting in waterlogging.
Podsols Profile (3)
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The C horizon forms from a range of
parent material (fluvioglacial sand or
till) or may be derived from acidic
parent rock.
Usage
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Podsols are not naturally fertile soils
and crop yields rapidly decline.
Lime needs to added to counteract the
podsol’s acidity and animal manure can
boost the poor quality of the humus.
Brown Earth Soils
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Brown Earth Soil have developed
beneath the temperate broadleaved
deciduous forests of Europe, Russia and
North America.
Brown Earth Soil Profile (1)
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The Ao horizon is rich in nutrients.
Because of the warmer climate the litter
decomposes rapidly resulting in mull humus.
Mull humus is less acidic than mor humus and
becomes well mixed with the soil materials
thanks to the activity of earthworms and soil
bacteria.
Brown Earth Soil Profile (2)
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The A horizon has a dark brown colour
because humus replaces minerals as they are
leached out.
Leaching is, however, less pronounced because
of a closer balance between evaporation and
precipitation.
The B horizon is less distinct (compared to
podsol) but is usually lighter in colour as
humus becomes less abundant.
Brown Earth Soil Profile (3)
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The C horizon is derived from varied
parent material which can range from
limestone to schists.
Plant roots can penetrate the C horizon
to extract minerals and ensure the
efficient cycling of nutrients through
the ecosystem.
Land Use
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Originally tree covered, these usually
mildly acidic, brown earth soils, have
been extensively exploited for
agriculture since pre-history.
Gley Soils
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Gley soils are found in sites which are waterlogged,
either permanently or temporarily.
When soil is waterlogged for a long time, its pore
spaces lose oxygen (anaerobic).
Such conditions mean that the decay of bacteria is
slowed down. In addition, iron compounds in the soil
are reduced chemically from their normal red-brown
colour to a blue –grey colour.
Gley Soil Profile
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The Ao and A horizons are darker reflecting
the presence of organic matter.
A large amount of organic material can
accumulate because of a lack of bacterial
activity necessary to create humus.
The B horizon is predominantly blue-grey,
indicating virtually continuous water-logging.
This has developed from a C horizon derived
from an impermeable clay layer.
Land Use
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Gleying is caused by the inability of soils
to shed water quickly.
Often found at the foot of slopes and
floodplains, gleys can support wetlands
and on occasions permanent pasture
Your turn
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Read page 165 – 167.
Answer Soil Types, Case
Studies question 2d.