Transcript powerpoint

Higher Geography
Biosphere
Factors influencing
Soil Formation
Introduction
There are six main interacting factors in
the formation of soil.
Parent Material – Biotic Factors –
Climate – Relief – Time – Human Activity
Parent material
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Parent material is especially significant
in the early development of soil and its
mineral content. It can vary from solid
bedrock to a wide range of
unconsolidated deposits including
alluvium, wind blown sand and glacial till.
Parent material influences (1):
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The rate of weathering: hard rocks (eg:
schist) weather slowly often leading to thin
soils. Softer, sedimentary rocks (eg: shale)
weather more quickly.
Chemical composition & soil colour: minerals
derived from quartzite and granite have a
relatively high silica content and are acidic;
soils on chalk and limestone are alkaline. The
darker the parent material the darker the
soil.
Parent material influences (2):

Soil texture: is influence by the size of
soil material particles. This is important
because it helps determine the
permeability of the soil and the relative
proportions of air (gases) and water.
Soil texture = the ‘feel’ of moist soil
Biotic Factors
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Involves the action of vegetation and a
wide range of organisms, from bacteria
to vertebrates.
They all interact, influenced by climate
and the evolving nature of the soil
itself, to produce the organic material
or humus.
Humus may include: (1)
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Mor humus - which mainly develops beneath
coniferous forest or heather moorland is
normally associated with a cooler, wet climate
and acidic parent material.
The litter layer of pine needles, cones and / or
heather shoots further encourages acid soil
reactions and discourages the breakdown of
plant material.
Earthworms are not common and there is a
limiting mixing of organic and mineral content.
Humus may include: (2)
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Mull humus – frequently develops beneath
deciduous woodland whose leaves are rich in
base materials.
With a plentiful supply of litter and a rich soil
fauna, there is no clearly defined humus layer.
Chemically the soil is almost neutral and is the
home to earthworms which are very active
decomposers.
Humus may include: (3)

Moder: is an intermediate humus
between mor and mull.
Climatic Factors (1)
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Climate is particularly important,
especially seasonal and daily variations
in temperature and precipitation.
At low temperatures the rate of soil
formation is slower, especially organic
decomposition. Equally, warmer
temperatures encourage decomposition.
Climatic Factors (2)
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The input of water percolating through
the soil is not the same as precipitation
but, providing precipitation exceeds
evaporation, leaching is a particularly
important process.
This occurs not just vertically but also
downslope.
Climatic Factors (3)

If evapotranspiration exceeds
precipitation, water and minerals may be
drawn upwards by the process of
capillary movement.
Relief (1)
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Relief or topography of land influences
drainage and soil depth.
Relief (2)
Upper well drained shedding site
from which there is surface run
off and through flow.
The lower receiving site
gains water, organic and
mineral matter.
If this site is
particularly badly
drained, excess water
accumulates and
encourages the
formation of gleys and
peaty soils.
Relief (3)

Relief and aspect can also modify the
effect of climate on the soil.
Shady north-facing slopes are colder and wetter
compared to those with a south-facing aspect. This can
slow up organic decomposition and encourage peat
formation.
Time
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Time is critical in the development of
soils before they are fully mature.
When they are young, soils retain the
features of the parent material.
Human Activity
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This should not be underestimated. It
started around 3000 BC ago when
humans started to fell woodland and
burn peat.
More recently, blanket planting of
coniferous plantations and modification
of soil chemistry by applying fertilisers,
lime and pesticides have further altered
soil characteristics.