Soils

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Soils

• Geography 12
• 2005-6

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Stages in soil forming processes
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Soil - is the top layer of the earths crust
that has been physically and chemically weathered
into small particles and in which vegetation
grows if temperature and precipitation are
favourable.

• 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.

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• 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 nutrient-rich 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.

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Laterite Soils
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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.
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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.
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Podzols Are often acidic and heavily leached .
They have a thin humus layer of decaying
evergreen needles at the surface.
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Podzols

• 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

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Chernozem

• Brown Chernozem
• Boreal Sub-Arctic of Alberta and Saskatchewan
• Often referred to as the Breadbasket areas of
  the world.

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• 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.

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• Grey-Brown
• Rapid accumulation of leaf litter into the A
  horizon is due to the high earthworm activity

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Sierozem

• Light colour of the A horizon indicates a very
  dry climate and little or no humus content
• 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.