Transcript Ecology Lecture 3 Ralph Kirby What is soil Before life invaded the land from the sea, there was probably little that looked like.

Ecology Lecture 3
Ralph Kirby
What is soil
Before life invaded the land from the sea, there
was probably little that looked like soil today
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Dust like Mars
Little organic matter
A few microorganisms perhaps
However, soil is the basis of all terrestrial life and
without soil, there would be no plants, no soil
microorganism and no land animals
Plants obtain many of their water and nutrients
from soil and it provides an place to attach to.
Definition of soil
Soil is hard to define because it is so complex
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Soil is a natural product formed by the weathering of
rocks and the action of living organism
Does it include the ability to support life
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Soil is a collection of mineral and organic matter than
can support plant growth
Does this include soil like material that does not support life
What if the climate at present does not support life
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The stratum below vegetation and above hard rock
What if there is no vegetation
Three dimensional matrix
Soil is a living system made up of a matrix
of minerals and organic matter that includes
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plants, both roots and stems
Bacteria
Fungi
Protozoa
Algae
Small animals
Larger animals
A unit of soil large enough to define is called
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Pedon
Formation of soil
Proposed that five factors are involved in the formation of soil
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Parent Material
Igneous rock
Sedimentary rock
Metamorphic rock
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Climate
Temperature
Rainfall
Elevation
Latitude
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Biotic Factors
Input factors from living organisms
Degradation by living organisms
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Topography
Water runoff
Draining
Erosion
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Time
Weathering, accumulation, decomposition and mineralization take time
Initial differentiation can be within 30 years
Formation of true soil, 2000 to 20000 years
Soil can age
Mechanical and Chemical Weathering
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Starting Point
Mechanical
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Water
Wind
Temperature
Creates loose material
Sorted and moved
Chemical
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Acids produced by lichens and mosses
Addition of organic matter
Oxidization
etc
Living Organisms
Without living organism there would be no soil
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Mars does not have soil as we know it
When plants colonized the land, they changed it by
producing soil
Plants introduce organic matter to soil
Microorganisms and small animals recycle the
organic matter to humus
Humus can be on top of soil in some acidic
environments
Humus is usually mixed with the soil and changes it
composition
Many microorganisms have evolved to fill this niche
Actinomycetales
Lignin degrading fungi
Soil has many
layers
O
Organic layer
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Fluctuates with season
A
Upper layer of mineralized
soil
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Large amount of organic
matter
E
Eluvial zone
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Maximum leaching
B
Illuvial zone
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Accumates leached
material such as clays,
silicates, etc
C
Unweathered starting
material
R
Rock or parent material
Soils show a great deal of
variation
Color
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No direct effect on how
soil function
Allows classification
Red
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Possibly oxides
Black
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Possible high organic
content
Texture
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Variation in size and
shape of soil particles
Gravel
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>2mm
Sand
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0.05mm to 2mm
Silt
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0.002mm to 0.05mm
Clay
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<0.002mm
Structure
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Space for roots etc
Pore space
Amount of water held
Rate of water movement
Aeration
Compaction
Aggregation
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Aggegates or peds
Depth
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Depends on
Slope
Weathering
Parent material
Vegetation
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Grasslands are deep
Forests are shallow
Water is essential for soils
See lack (?) of water on Mars
Soil can become saturated if all
pores filled
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Normally at field capacity
Capillary water is usually
present
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Extracted by plants
Available water capacity
Hygroscopic water unavailable
Drainage
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Low drainage results in low
aeration
All affected by soil texture
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Sand
Lower capacity
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Clays
Higher capacity
Plants need minerals in the form of
ions
Cationic exchange resin
type structure
Change in pH affects
binding capacity for ions
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Immovable
Hydrogen
Aluminium
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Removable in order
Calcium
Magnesium
Potassium
Ammonium
Sodium
Soils vary with climate and vegetation
Entrisol
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Mountains
Where soil making process has
been interupted by flooding etc
Inceptisol
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Mineral rich mountain soil
Forests and pasture
Aridisol
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Arid regions
Low in humus
Salinization due to low rainfall
Andisol
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Volcanic in origin
Can be very fertile
Mollisol
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Dark organic rich A layer
Deep fertile
Spodosol
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Acidic
Coniferous forest soil
Alfisol
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Temperate forest
Organically rich
Ultisol
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Warm climate soil
Redish or yellowish
Low nutriant content
Oxisol
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Wet subtropical/tropical soil\
Lots of water movement through
soil
Low nutrients
Histosol
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High water table
Poor drainage
Peatlands
Gelisol
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Permafrost
Vertisol
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High % clay
No B horizon
Swell and shrink
Pasture
Soil forms a biotic ecosystem on its own
Biotic System in soil
Needs
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Living space
Varies with soil type
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Oxygen
Varies with water saturation
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Food
Varies with plant cover
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Water
Can vary with climate
Environment is relatively constant
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Water can change dramatically
Mechanisms to survive drought
Spores etc
Only upper layer is really available
Diversity is very very large
The ecosystem is largely not understood in detail
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Particularly the microorganisms
Man has an effect on soil
Changes in plant cover
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England
1000 BC
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Forest
2004
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Cities, towns, villages, farm land, monoculture forests
Erosion
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Deforestation in Africa
Climate change
Dams
Roads and storm drains