Soil Flashcards
What essential functions does soil perform?
Reservoir for water (aquafiers etc), medium for plant growth and food, filters the air and the water, recycles dead plants/animals, storing huge amounts of carbon
Main components of soil
45% mineral. 25 % air. 25% water. 5% organic
Mineral part of soil
Formed by weathering of parent material.
Primary minerals = changed little since formation
secondary minerals = formed from breakdown and chemical weathering of less resistant primary minerals
Soil litter
remainder of decomposed animal and plant waste
Soil humus
A dark and organic material that forms in soil when plant and animal matter decays
Soil biomass
living organisms and plant roots
Mineralisation
The process where the breakdown of organic matter by microorganisms leads to nutrients being released such as nitrogen, carbon and phosphorus
Water in soil
Important as it is required for parent material weathering.
Saturated soil
When all the soil is saturated the pores are filled with water
Soil air
The air within the soil occupies the pore spaces within the soil (if it is not saturated with water that is)
Soil profile
Vertical section through the soil from ground surface down to the parent material.
Soil horizons
The layers within the soil profile.
O, A, E, B, C, R
O horizon
Basically the surface layer (soil humus). Consisting of organic matter (decay of animals and plants). Not always present.
A layer
The topsoil.
Contains rich organic material with minerals. High concentration of organic matter and microorganism.
E horizon
Elevation layer (may be missing in some soils) Mineral horizon. Lighter in color. Leaching happens here
B horizon
Mineral horizon but enriched in iron
Soil of acculumation.
C horizon
Loose material. Much of original material and fragments. often light in color.
R horizon
Bedrock. Form parent material.
Pedogenesis
Process of soil formation. The soil horizons develop after number of processes.
Processes like weathering, winds, rain etc.
A rock splits and expands leading to smaller particles entering the soil with new minerals.
Addition of pedogenesis
Comes from parent material. Can also be material gathered by wind or energy from the sun
Losses of pedogenesis
Removals from soil because of erosion or filtering
Mixing of pedogenesis
Mixing of organic and inorganic components is carried out by soil animals and plant roots or by freezing of water and shrinking/swelling.
Humans = ploughing
Factors affecting soil formation - Climate
Perhaps the most influential factor. Determines the moisture level and temperature and therefore amount of precipitation (affecting weathering).
Climate impacts weathering and the process of transforming the soil into different minerals (clay for instance)
Influences which productivity occurs of photosynthesis and therefore the amount of biomass integrated into the soil (A-horizon)
Little precipitation often leads to salinization and calcification
Factors affecting soil formation - topography
Altitude = can quickly change climatic conditions (usually drier and colder)
Higher slopes = allows for more erosion.
lower temp = less biological activity and less decomposition of organic matter
Dry podzol on top of steeper soil
Wet podzol further down
Lower topography often peat
Factors affecting soil formation - organisms/flora&fauna
Earthworms or other small animals mix and freshen the soil which creates pore spaces
Found to increase the infiltration rate
Could be animals, plants rooting or even humans ploughing that change biological factors such as moisture
Factors affecting soil formation - time
Time continually forms the parent material under the influence of the other factors.
Sedimentation and depositing takes time.
Important to be aware of the fact that soil processes are usually very slow and certain conditions are needed for changes to occur.