Biosphere Lecture 2

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What are soils?
Soil is defined as the top layer of the earth’s crust (the skin of the Earth).
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Soil is a dynamic three phase system:
solid (mineral particles+ organic matter), liquid (water+ salts), gas (air) plus living organisms. It is in fact an extremely complex, variable and living medium
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Soils containss around twice the amount of
carbon in the atmosphere and three times the amount to be found in vegetation.
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As soil formation is an extremely slow process,
soil can be considered essentially as a non-renewable resource.
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Soil Inputs
Mineral weathering(parent material or transported) Organic matter (above and below ground biomass)
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Soil Outputs
Erosion (wind and water) Leaching
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Soil Mixing and translocation
Bioturbation Physical processes
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Leaching is the
is the loss of mineral and organic solutes due to percolation. It is a mechanism of soil formation distinct from the soil forming process of eluviation, which is the loss of mineral and organic colloids. Leached and elluviated materials tend to be lo
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. A soil horizon accumulating leached and eluviated materials is referred to as a zone
of illuviation.
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Soils form on Parent material aka
Rock surfaces ,Unconsolidated materials (Glacial Till)
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The fertility of a soil is its ability to support a
desired crop (yield & quality).
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Soil must provide:
Water – water holding properties Air ~ porosity & humidity Nutrients – cation exchange capacity and nutrient availability
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Soil texture –
relative proportions of soil separates (particles of a certain size).
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Soil structure
– the arrangement of individual mineral particles into larger aggregates of peds
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Porosity –
the total volume of pore space in soil is its porosity or air capacity. It is calculated comparing the bulk density of the soil to the individual mineral particle density.
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Prosity varies between
10-70%
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Porosity – when the soil is very compacted (high bulk density) the porosity
is low, when the soil has low bulk density (lots of gaps between particles) it has high porosity.
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Wilting point:
below this point, plants are unable to extract water from the soil
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Field capacity:
wetness after loss of water by gravitational forces has occurred
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. Air - soil aeration influences the availability
of many nutrients.
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Roots need air to
respire
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Nutrients in the soil are present:
In soil solution (soluble nutrients) As ions adsorbed to clay particles or to organic matter. Inside organic molecules Inside the mineral structure
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Which nutrients are the least bioavailable
the ones inside the mineral structure
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How many elements in total
13
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What catergories are elements divided into
macro and micro nutrients.
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only four are negatively charged
P (marco), S,(MAcro) N (macro)(also in postively charged form in the form of ammonium) and Cl (micro)
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Adsorption – how do these nutrients attach?
Clays are structured in layers or sheets, and on the surface, they have charges dependent on pH. Permanent charges due to isomorphic substitution
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Adsorption –
cation exchange capacity (me 100g-1)
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CEC =
capacity of the negatively charged particle surface to attract positively charged ions (cations).
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. Nutrients – c) Inside organic molecules d) Inside the mineral structure They are not bioavailable because
) needs to be digested by microorganisms, d) needs to be weathered.
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the importance of soils
Soils support all terrestrial ecosystems They take thousands of years to form Provide nutrients Store water Provide habitat
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Human impacts on soils
Contamination Acidification Salinisation Compaction Loss of organic matter Erosion
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Importance of organic matter
Improves water holding capacity Improves aeration Supplies the nutrients plants need to grow Loss of organic matter results in reliance on fertilisers Binds mineral particles together Reduces erosion rates
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Slash and burn agriculture is
not sustainable in the long term
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In the tropics, soil erosion has
a major effect on crop yield
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Up to 2 billion people live in
drylands
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Card 2

Front

Soil is a dynamic three phase system:

Back

solid (mineral particles+ organic matter), liquid (water+ salts), gas (air) plus living organisms. It is in fact an extremely complex, variable and living medium

Card 3

Front

Soils containss around twice the amount of

Back

Preview of the front of card 3

Card 4

Front

As soil formation is an extremely slow process,

Back

Preview of the front of card 4

Card 5

Front

Soil Inputs

Back

Preview of the front of card 5
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