Soil Formation Flashcards
How does soil formation begin?
Rock mineral and organic matter combination
Combination of rock mineral and organic matter…
Rock minerals cannot support plant growth, organic matter not structurually sound
Volume ratio of soil…
RM/OM 50% whilst pores the other 50%
What determines physical properties of soil?
Mineral compostion of the parent rocks
What are carbonate rocks ade of?
Limestone and chalk made of prehistoric animals, whilst coal of plants
How do silica?silcates form?
Silicon combines with O2, the less the easier they break up
What is silica content based on?
Magma solidifcation,
Rock classifications based on silica…
Ultrabasic -45
Basic - 45-55
Intermediate 55-65
Acidic -65-85
Fractional Crystallisation
Removal of early formed crystals from homogenous magma so these crystals prevented from further reaction with the residual melt
SO2 formation…
Foun in silica rich magma formed by fractional crystallisation associated with continental crust, then magma rise and cooling
What is silica enrichment in magma based on?
Quartz, feldspar and micas high melting points, crystalling first
Bowens Reaction Series
Explains order of mineral crystallisation with cooling
Types of weathering?
Physical
Chemistry
Example of physical weathering?
Different mineral compositon, different rates of thermal expansion
What causes exfoliation?
Temperature difference between inner-outer parts of rock causes
Example of mechancial weathering…
Freeze-thaw
Examples of chemical weathering…
Hydrolysis, carbonation, hydratio, dissolution, oxidation/reduction
Carbonation
This is caused by biological activity with CO2 respiration and dissolution in H2O forming carbonic acid
Hydration
This is mineral water absorption without ion formation
Dissolution
This is minerals dissolving in water like NaCl and KCl
Oxidation/Reduction
This is the take up and removal of oxygen or electrons
Soil Organic Matter
All dead and living life, based on carbon content being 58% of total weight of organic matter
How does OM contribute to soil?
Binds soil particles in to aggreagtes, supplies nutrients to plants
Colloidal Particles
Form electrostatically with water and minerals and organic matter
What does OM include?
Microbial biomass, decaying organic matter
Hydrophobic Interactions
Repel water, allowing hydrophobic organic mollecles to associate with each others
Extracellular Polymeric Substances
Produced by microbes bind soil particles together
Chemical groups involved in soil…
Hydroxyl, amino and carboxyl groups interact with soil minerals
What is SOM made of?
Hemi/Cellulose
Proteins/Amino acids 5%
Lignin 15%
Fats/waxes 1-5%
What does SOM accumulation depend on?
Plants
How do plants form soils?
Primary colonisers of microorganisms in water are rqeuired like nitrogen fixers
How do lichens colonise?
Surplus nutrients passed to fungi frfom N2 fixers releasing acidic compounds breaking down mineral rock, releasing minerals for algae
Example of soil condition climate variability…
Upland UK soils being acidic supporting Ericaceae being acid-tolerant, resistant to microbial attack due to high lignin
Three types of soil…
Sand(0.06-2mm)
Silt
Clay (2mm)
Primary cause of chemical release from rock?
Hydration, hyrdolysis and dissolution
What can release priamry nutrients do?
Recrystallise forming secondary clay minerals,
How are clays classified?
Alternating Alo2 and silica sheets
Humus
Conglomerate of organic material formed by humification
Layetrs of Soil…
O Horizon
A Horizon
E Horizon
B Horizon
How is the O horizon divided?
Litter, fermentation and humic layers
How does Mull form?
Neutral/acidic oconditions, mineralise residues and high soil organisms break down OM, mixing with underlying mineral says
Types of vertical movment?
Leaching and Eluviation
What does leaching do?
Removes soluble compounds under extreme weathering like humid tropics, weathering clay
5 Soil forming cators by Hans Jenny…
Climate, parent material, topography, organisms and time
What are four types of soil profile?
Podzol
Gleysol
Ferrasol
Histosol
Podzol
Foudn in cool, humid and temperate regions, containing large O horizon
Gleysol
Found in northern latitudes from drainage impairemnt, from waterlogging
Ferralsol
Occupy tropics with high temperature and rainfall like enctral africa and south america
Histosol
Peats, covering Northern Europe, Canada and Russia.
