Transcript Soils - sabresocials.com

Soils
Geography 12
2005-6
Stages in soil forming processes
Soil - is the top layer of the earth’s crust that has been physically and chemically
weathered into small particles and in which vegetation grows if temperature and
precipitation are favourable.
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Soil forming processes:
1. Decaying vegetation forms humus. Soils
high in humus are generally very fertile.
2. Leaching. Water infiltrates into the ground
and dissolved minerals are carried deep into
the sub soil and away. Common where
rainfall is heavy.
3. Capillary Action. When surface layers are
dry water is transferred from deep in the
ground to the surface. As transpiration
occurs and evaporation water is dran up
through the roots to the leaves and through
the soil. Capillary action brings water and
dissolved minerals close to the surface. Great
for plants. (but) Common in dry desert
regions.
4. Translocation. This is the movement of
solid material from on place to another by
water or by animals. Helps to mix the soil.
• Soil forms over many thousands of years from weathered rock
fragments by physical and chemical weathering and decayed
remains of living organisms. This is referred to as parent
material.
• As soil develops, it forms distinct layers, known as horizons.
• Each horizon has a specific colour, texture, and mineral
content
• The number and type of horizons in a particular soil vary, but
in general the uppermost horizon of soil forms the nutrientrich topsoil.
• Beneath the topsoil lies the subsoil, which contains minerals
that have trickled down from the topsoil.
• Rock fragments reside below the subsoil
• The horizon forming the foundation of soil consists of
unweathered parent rock.
Laterite Soils
Latosols or larerite soils arise in
the tropical rainforest biome in the
equatorial zone where high
temperatures and high precipitation
occur throughout the year. Climatic
conditions permit the highest net
primary productivity of all the
terrestrial biomes, and extensive
chemical weathering leads to the
development of deep soils, often
reaching 20 m to 30 m (65 ft to 100
in depth. Tropical soils have a
loose structure and if there is
deforestation that removes vegetation
cover and roots they suffer rapid
erosion because of the heavy rainfall.
This may result in loss of fertility and
many attempts at cultivation of
latosols have, in fact, been
unsuccessful.
Laterites are among the most infertile soils in the world!
The tropical soil is very deeply
weathered and red due to its high
iron-oxide concentration.
A continual drop of leaves from
the broadleaf evergreen forest
adds nutrients to the soil.
Without this continual leaf litter,
the nutrients would be quickly
leached down..
The trees shallow root system
allows them to quickly capture
these nutrients before they are
washed away.
Podzols:
Are often acidic and
heavily leached .
They have a thin humus
layer of decaying
evergreen needles at the
surface.
Podzols
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Podzol soils are mainly found in
the taiga (boreal forest) biome
at high latitudes and at higher
altitudes in temperate latitudes.
Podzols form under a harsh,
cold climate where growth is
slow during the winter months
and snow accumulates and
stays on the ground for long
periods.
The vegetation consists largely
of coniferous trees, which are
specially adapted to the
climatic conditions,
Productivity is low due to the
climatic conditions. The soils
are impoverished and the
climate is unsuitable for
agriculture, but is suitable for
commercial forestry
Chernozem
• Brown Chernozem
• Boreal Sub-Arctic of
Alberta and
Saskatchewan
• Often referred to as
the “Breadbasket”
areas of the world.
• Chernozem soil of
temperate grassland
areas
• Fertile with thick
humus layer
• Due to climate
leaching is not a
problem
• Capillary action is
good and cold winters
force small animal
down.
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Chernozem soils occur under the
temperate grasslands of the steppes
of Russia, the prairies of North
America, in Australia, South Africa,
and the Pampas in South America
(all approximately 30-40° north and
south of the equator). T
The vegetation is mainly grasses
and herbaceous plants, which have
become dominant following natural
and accidental fires and extensive
human modification of these regions
over time.
Although initial ploughing is difficult
because of a dense mat of roots,
once cultivated, these soils are
regarded as the best in the world
for agriculture. They have high
nutrient levels, good humus
content, and good texture and
structure.
Chernozem soils support the major
grain growing belts of the world.
• Grey-Brown
• Rapid accumulation of
leaf litter into the A
horizon is due to the
high earthworm
activity
Sierozem
• Light colour of the A
horizon indicates a
very dry climate and
little or no humus
content
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The light brown A horizon at the surface occurs
because of the lack of organic matter or
moisture which usually darken the soil. There is
very little vegetation growing here, and so
organic matter is not returned to the soil. When
rainfall does occur in this environment, it carries
materials downward into the profile to form B
horizons. The white streaks near the bottom of
this profile are formed from deposits of calcium
carbonate which become very hard as they
accumulate over time
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Tundra occurs in the extreme
northern parts of Alaska, Greenland,
Russia, and Canada to the north of
the taiga.
The climate is very harsh, and the
temperatures rarely rise above 0°
C, so the ground is permanently
frozen.
Precipitation accumulates as snow
for most of the year. In the short
summer temperatures rise
sufficiently for a few centimetres at
the surface of the soil to thaw.
Plant growth is limited by the cold
temperatures and lack of available
water; lichens, mosses, and low
shrubs predominate.
The cycles of freezing and thawing
with the changing seasons causes
the weathering of rock by frost
shattering. Frost heave can occur,
whereby broken rock fragments are
brought to the surface.
No clear horizons are developed.