biosphere soil. what is soil? n soil is a mixture of particles of weathered rock, decayed organic...
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Biosphere
Soil
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What is soil?
Soil is a mixture of particles of weathered rock, decayed organic matter, water and gases in which living organisms are present.
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Occupy the spaces in the soils
Water
Minerals from the physical / chemical weathering of the parent rock
MineralsAir
Lacks light, Varies in proportions
Organisms
Decaying roots, leaves, animals broken down by organisms and micro-organisms
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Mineral matter
Minerals derived from parent material by physical and chemical weathering
Largest component in terms of volume 45% in a typical topsoil
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Organic Material
Mainly derived from decaying roots, leaves, needles and remains of dead organisms
Broken down by micro-organisms, worms and moles
5% volume in a typical topsoil
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Air and water
Ever changing volumes which fill the voids - the spaces in the soil
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Soil Profile
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Soil Profiles
A soil profile is a vertical section through the soil from surface vegetation to the bedrock
Soils can be identified by looking at distinct layers or horizons
Usually 4 distinct horizons can be identified in a soil
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Soil Profile - Ao Horizon Surface organic layer - decaying vegetation.
Subdivided into 3 layers L(litter) - leaves , pine needles, cones or dead
heather shoots F(fermentation layer) - organic material starts
to decompose H(humus) - decomposed remnants of
vegetation, animals and bacteria. Important source of nutrients for soil below
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Soil profile - A Horizon Main top layer Consists of a mixture of organic and
inorganic material. Organic material is introduced from Ao
layer Usually nutrient rich and fine textured Eluviation - washing out of minerals The topsoil
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Soil profile - B Horizon The subsoil less organic material and courser in
texture due to importance of weathering Soluble material can be leached out of
A horizon into B horizon Leaching is the removal of soluble
minerals Illuviation - washing in of minerals
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Soil profile - C Horizon
Zone of the regolith large particles sit upon the bedrock Physical and chemical weathering of
parent material is source of nutrients
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Soil Formation - Factors
5/6 factors are seen to be important in influencing the formation of a soil
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Soil Formation – 1)Parent material (13 bullet points)
Significant in early stage of soil development
can vary from solid bedrock to deposits such as alluvium and glacial till
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Soil Formation - Parent material
Rate of weathering Hard rocks such schist (metamorphic
rocks) weather slowly leading to thin soils
Softer sedimentary rocks such as shale weather more quickly
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Soil Formation - Parent material Chemical composition and soil colour soils from granite have high silica
content and are acidic Soils on chalk and limestone are
alkaline Silica rich soils are light in colour Rocks such as basalt have high iron
content and form dark soils
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Soil Formation - Parent material
Soil texture the feel factor is influenced by the size
of the soil particles determines permeability of soil
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Soil formation – 2) Biotic factors (1 bullet point)
Involve the action of vegetation and organisms. They interact, influenced by climate to produce humus. This may lie below the L and F layers of the Ao horizon or mixed through the whole A horizon
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Soil formation - 3) Climate(5 bullet points)
At low temperatures soil formation is slower particularly organic decomposition
Warm temperatures encourage decomposition and production of organic material in the soil
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Soil formation - Climate
Water percolation also affects soil Where precipitation exceeds
evaporation, leaching is an important process
Where evaporation exceeds precipitation water and minerals are drawn to the surface by capillary movement
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Soil formation – 4) Relief(3 bullet points)
Upper slopes - runoff and through flow of water
Lower slopes gain water organic and mineral material
Shady north facing slopes are colder and wetter than south facing slopes
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Soil formation – 5) Time(3 bullet points)
Critical to development of soil When soils are young they retain
features of parent material Scottish soils are young mostly as a
result of last glaciation
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Soil formation – 6) Human Activity(3 bullet points)
Prehistoric people began to fell woodland around 3000 BC
Accelerated naturally occurring soil erosion
More recently planting blanket coniferous forest and the application of fertilisers have altered soil characteristics