Transcript Soil profiles - Mr Murray Geography

Biosphere
Soils
Soils — properties and formation processes:
♦ properties of podzols, brown earths and gleys —
horizons, colour, texture, drainage
♦ the influence of soil-forming processes on profiles as
demonstrated by podzolisation, gleying, organic and
nutrient movement
SQA
Biosphere Soils Terminology
Pedalfer soil: soils where precipitation exceeds evaporation– wet areas.
Pedocal soil: soils where evaporation exceeds precipitation – dry areas.
mor: acidic humus associated with coniferous forests/tundra areas
mull: chemically neutral humus associated with deciduous forests
anaerobic : without oxygen
gleying : waterlogging
eluviation : movement of humus, chemical substances, and mineral particles
from the upper layers of a soil to lower layers by the downward movement of
water through the soil profile
illuviation : Deposition of humus, chemical substances, and fine mineral
particles in the lower layers of a soil from upper layers because of the
downward movement of water through the soil profile
Biosphere Soils What is soil?
Soil is a mixture of weathered rock, decayed organic matter, water and
gases.
Mineral matter. This consists of minerals from chemical and physical
weathering of the parent material.
Organic material. Material from decaying plants and organism.
Air and water. Ever changing and fills the voids or spaces in the soil.
Soils is a mixture of...
Decayed organic
matter
Leaves
5%
22%
40%
Water
Air
23%
Dead soil biota
10%
Biosphere Soils Soil forming processes
Climate
Time
Drainage
Relief
Soil
formation
Parent
material
Vegetation
Humans
Soil biota
Biosphere Soils Soil forming processes
Climate
Climate
Temperature and precipitation have a major influence on the soil.
Higher temperatures encourage soil biota activity whilst the opposite
is true.
In wetter areas where, precipitation is greater than evaporation, this
causes the leaching of the soil and the removal of soluble minerals
and humus. However where evaporation is greater than
precipitation, water actually moves upwards through the soil, called
capillary action, and this brings minerals from deeper down up to the
surface.
Biosphere Soils Soil forming processes
Relief and drainage
Relief and drainage
A steep slope will allow water to run-off and increase the chances of
soil erosion. Flat land is usually poorly drained and this
waterlogging can prevent soil forming properly.
Aspect can lead to south-facing slopes being warmer and
encouraging biota activity and vegetation more so than in northfacing slopes.
The ease with which
water can pass through
as soil can also affect its
development.
Biosphere Soils Soil forming processes
Vegetation
Vegetation
Vegetation provides plenty of humus aiding soil fertility. Soil biota
activity is encouraged and these areas are more likely to be warm
and moist further improving soil fertility. The type of vegetation
present will affect the type of soils that develops.
Biosphere Soils Soil forming processes
Humans
Humans
People increasingly cause change in soils. By clearing woodlands in
one area, planting trees in another, growing crops, adding chemicals
and fertilisers, draining marshes the soil is altered much more
quickly than would occur naturally.
Biosphere Soils Soil forming processes
Soil biota
Soil biota
This is all the animals living in the soil. Bacteria, worms, plants,
roots and insects all absorb nitrogen, mix the soil by burrowing
through it, and also aerate it (create air pockets that can be filled by
water). The decaying humus in the topsoil makes this the most
fertile section of any soil.
Biosphere Soils Soil forming processes
Parent material
Parent material
This is the main rock type under the soil, usually the bedrock
(regolith). The parent material affects the colour, texture and
chemical make-up of the soil. Eg red sandstone bedrock produces
red, “sandy” soil.
Biosphere Soils Soil forming processes
Time
Time
Long periods of time are needed for soils to reach maturity by the
processes already mentioned (about 1000 years for one cm - in many
parts of Britain we have had only 10,000 years since the last Ice Age
stripped the original surface soils away). It is thought that 10 000
years are needed for a soil to settle and mature.
Biosphere Soils Soil profiles
A soil profile is a vertical section from the surface vegetation to the bedrock.
By examining the different layers or horizons it is possible to work out the
soil type.
The A Horizon: This is the main layer
and consist of a mixture of organic and
inorganic material. This is usually
nutrient rich and fine textured. Often
referred to as topsoil.
The B Horizon: This is the
subsoil, which contains less
organic matter and is coarser
in texture, reflecting the
importance of
weathering.Nutrients may
leach out of the A Horizon.
The C Horizon: This is the
zone of regolith (fragments of
rock). Large particles sit on
the underlying bedrock.
Topsoil
Subsoil
Soil
profile
Regolith
A
Horizon
B
Horizon
C
Horizon
Soil profile can vary in depth. In
Britain the average depth is 1.5m
Biosphere Soils Brown Earth forest soils
Biosphere Soils Brown Earth forest soils
Biosphere Soils Brown Earth forest soils
Location: Temperate deciduous forests of Central Europe, Russia and North
America. Further south than podsols.
Climate: Moderate climate. Milder winters, cooler summers and lower
precipitation, allowing more rapid decomposition – although it is still exceeds
evaporation (pedalfer). Good conditions for vegetation growth/soil biota.
Relief & drainage: Gently rolling landscape, allows soil to drain well.
The A horizon is greasy due to its high organic content and is a light brown
colour due to the humus. Leaching occurs but is less than in other soils from
wetter areas, but where it is more pronounced an iron pan may develop in
the B horizon.
Soil biota: Warmer temperatures encourage soil biota activity, making
horizons less distinct. Leaf litter is more rapidly decomposed.
Biosphere Soils Brown Earth forest soils
Natural vegetation: Deciduous forests (ash, beech, oak). Plentiful supply of
leaf litter. The resulting humus is deep and only slightly acidic (mull).
Type of soil: Horizons here a less distinct due to more soil biota activity
mixing the layers. A pedalfer soil, but less acidic.more alkaline soil due to
leaf litter type.
Processes: Climate is less of a negative influence – mixing is promoted vis
biota and some gentler leaching may occur, possible leading to the
development of an ironpan.
Parent material: Weathering of the parent material contributes to the soil
forming process here.
Human use: More fertile and useful than the other main soil types and
populations here are greater. With the addition of manure and fertilisers
these soils support grain crops and grazing cattle.
Biosphere Soils Brown earth soils
Precipitation = evaporation approx
Deciduous trees/
heathers/shallow roots
A
Horizon
Mild acid humus with plant foods
Brown layer –
well aerated
Dark brown layer
No marked
horizons
B
Horizon
Thick leaf debris
Merging boundary due to mixing by biota
Lighter brown layer
Deep brown layer
C
Horizon
Parent material
Biosphere Soils Podsol soils
Biosphere Soils World biomes - Podsol soils
Biosphere Soils Podsol soils
Location: Northern coniferous forests.
Climate: Long cool/cold winters and short mild summers. Precipitation can
be variable – low to fairly heavy. Considerable snowfall though leading to
spring snow-melt.. Leads to low soil biota activity and slow decomposition.
Relief & drainage: On mountain sides or tops, up to 350m. Precipitation and
drainage leads to rapid leaching of iron and aluminium oxides (eluviation)
from the A horizon leaving it rich in silica and ash-grey in colour.
The deposition of iron oxides in the B horizon (illuviation) creates a redbrown colouring and may concentrate to forma thin solid layer called an iron
pan. This impedes drainage and can cause waterlogging.
Soil biota: Not much activity here because of the cold climate and this
means that the soil is not mixed, leading to clear horizons developing.
Biosphere Soils Podsol soils
Natural vegetation: Coniferous trees (pines, spruces, firs). Produces litter of
needles and pines, creating a thin acidic humus (mor).
Type of soil: Heavy with aluminium and iron, leading to an acidic pedalfer
soil. This soil has clearly defined horizons.
Processes: The climate has a strong influence here, ie lack of warmth limits
soil biota activity restricts mixing of soil and causes humus to decay slowly;
and leaching of iron and aluminium, as spring snow melts, and humus causes
an iron pan to develop.
Parent material: This only has a small influence with podsols.
Human use: Mainly used for commercial forestry plantations (conifers). If
lime were added, some cultivation could take place with oats, potatoes or
hay. Waterlogging due to the ironpan is a major problem.
Biosphere Soils Podsol soils
Precipitation > evaporation
Coniferous trees/
heathers/shallow roots
A
Horizon
B
Horizon
C
Horizon
Layer of needles and cones
Raw,black acid humus (mor)
Sandy
texture
Ash grey layer
Iron pan – impedes drainage
Reddish brown layer
Denser
texture
Parent material
Biosphere Soils Gley soils
Biosphere Soils Gley soils
Biosphere Soils Gley soils
Location: Found in Tundra areas, or in places with poor drainage and low
temperatures eg Dartmoor (SW England)
Climate: Cold and wet. Summers are mild and brief and severe winters limit
soil biota activity. The important factor here is the lack of warmth. The
continual process of freezing and thawing, and consequent expansion and
contraction, leads to vertical mixing of soil particles and poorly defined
horizons. The presence of permafrost impedes drainage.
Relief & drainage: Wet and exposed flat regions with very poor drainage - the
soil is damp/waterlogged due to the permafrost. The presence of water here
causes a lack of oxygen (anaerobic conditions), leading to a gleying of the
soil, turning it blue-grey in colour and greasy to the touch.
Soil biota: Severely restricted due to extreme cold and waterlogging. Soil is
mixed by freeze/thaw action, but very slowly.
Biosphere Soils Gley soils
Natural vegetation: Vegetation growth is limited due to lack of warmth and
waterlogging. Typically mosses, lichens and marsh vegetation dominate.
Larger plants can’t survive due top the shallow soils (permafrost). Produces
a dark, acidic humus (mor).
Type of soil: Pedalfer soil. Clearly defined horizons.
Processes: As the soil is usually waterlogged it is deficient in oxygen, limiting
soil biota activity. Litter is broken down very slowly in the cold temperatures.
This soil is closely linked to the climate and vegetation.
Parental material: Fragments of parent material are moved through this soil
by freeze/thaw action.
Human response: Limited potential for humans so populations are scarce. By
ploughing, liming and fertilising/manuring this soil is still only capable of
growing low value crops such as oats or potatoes. These areas are remote
from population centres though so profits would be hard to make with such
crops.
Biosphere Soils Gley soils
Precipitation > evaporation
Mosses and lichens
A
Horizon
Silty texture
B
Horizon
Grassy meadowland/small shrubs
Black with acid humus (mor)
Waterlogged blue grey gleyed mud
Angular rock fragments
Waterlogged
Permafrost
C
Horizon
Parent material
Impermeable
clay
Biosphere Soils Summary
Brown Earth forest soils
Summary:
 Precipitation is slightly greater than evaporation, leading to a downwards
movement of water and moderate leaching. A narrow hard pan can
sometimes develop.
 Faster decomposition due to warmer temperatures and less water. Lots of
soil biota activity – worms, rodents, insects.
 Litter is mainly from deciduous leaves, leading to only a mild acid humus.
 Clearly defined horizons.
Biosphere Soils Summary
Podsol soils
Summary:
 Precipitation is greater than evaporation, leading to a downwards
movement of water and leaching.
 An iron/aluminium hardpan is formed which acts as a barrier to drainage.
 Low temperatures result in limited biota activity and a slow
breakdown/decomposition of litter.
 An acidic (mor) humus develops due to the layer of pine needles/fir cones.
 Clearly defined horizons.
Biosphere Soils Summary
Gley soils
Summary:
 Damp waterlogged soils. Inadequate drainage. Permafrost layer may be
present.
 Poorly defined horizons.
 Dark, acidic (mor) humus develops from the slowly decaying mosses,
lichens and harsh vegetation.
 Limited soil biota activity due to waterlogging and low temperatures, so
little biological activity. Humus decays very slowly.
Biosphere Soils Soil profiles
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Soil
profile
Biosphere Soils Brown earth soils
Precipitation = evaporation approx
Deciduous trees/
heathers/shallow roots
A
Horizon
Mild acid humus with plant foods
Brown layer –
well aerated
Dark brown layer
No marked
horizons
B
Horizon
Thick leaf debris
Merging boundary due to mixing by biota
Lighter brown layer
Deep brown layer
C
Horizon
Parent material
Biosphere Soils Podsol soils
Precipitation > evaporation
Coniferous trees/
heathers/shallow roots
Layer of needles and cones
A
Horizon
Raw,black acid humus (mor)
Sandy
texture
Ash grey layer
Iron pan – impedes drainage
B
Horizon
C
Horizon
Reddish brown layer
Denser
texture
Parent material
Biosphere Soils Gley soils
Precipitation > evaporation
Grassy meadowland/small shrubs
Silty texture
A
Horizon
Black with acid humus (mor)
Waterlogged blue grey gleyed mud
B
Horizon
Waterlogged
Angular rock fragments
Permafrost
C
Horizon
Parent material
Impermeable
clay