7 Soils Flashcards
weathering
the disintegration (physical breakdown) and decomposition (chemical alteration) of rocks at or near the earths surface, without any movement of the materials
mass wasting
the movement of material down slope under the influence of gravity
erosion
the physical movement of material by a medium such as water wind or ice
frost wedging or shattering
a type of weathering where water fills the internal spaces of rock, when the water freezes it expands applying pressure to the rock. the rock will eventually crack and break up
How can biological activity cause weathering
-roots of trees and shrubs often grow into cracks and joints of rocks. as the trees grow, they exert pressure on the rock causing the crack to widen.
-burrowing animals can weaken land areas, ultimately leading to collapse with the loosened and broken rocks and soil easily washed away or exposed to further weather effects
salt crystallisation
when water evaporates it leaves behind dissolved mineral content. these minerals then crystallise. the froth applies pressure to enclosing rock
soil
soil is the upper layer of the earths crust, supporting plant growth and providing a critical bridge between and biosphere and mineral content of the geosphere.
-it consists of minerals, organic matter, air, water and living organisms
climate affecting soils
the combined effects of rainfall, tempt and seasonal changes.
-in cold dry regions (deserts and polar and alpine environments) soils are typically thin and contain little organic matter
-in hot and wet environments (equatorial and tropical regions) there are better plant growth which adds organic matter after decomposition, resulting in thick soils rich in organic matter
What does Horizon A consist of?
Contains humus and is a zone full of intense biological activity by plant roots worms insects microorganisms and other life forms.
Old, well developed soils contain less soluble minerals due to leaching, leaving behind insoluble minerals like clay and quartz
Humus
Humus is dark, organic material that forms in soil when plant and animal matter decays.
What does Horizon B consist of?
Bright colours and contains little organic matter except deep plant roots.
Contains concentrated soluble minerals and iron oxides from leaching
What does Horizon C consist of?
Contains clay mixed with Brocken pieces of bedrock
topography
-soils on steep slopes are usually thinner than those on flat or gently sloping areas
-sloping soils move downhill with erosion
What does Bedrock consist of?
Bedrock is the underlying rock of an environment formed from weathered and broken down rock. It doesn’t show real development in soil so not strictly considered a horizon.
water movement (two types and effects)
-water movement within soil can be lateral (sideways) and vertical (leaching)
-lateral movement causes transport of soluble material or even entire soil horizons
-vertical movement of water through soil is called leaching. it removes soluble minerals from the A horizon, then concentrated in the B horizon
Time
-is required for all of the factors mentioned above.
-after an event like a landslide, that mixes soil into an unaltered mass, it can take between hundred and thousands of years for a clear horizon to redevelop
What is responsible for soil thickness?
Rocks which are more resistant to physical/chemical breakdown form thin rocks eg quartzite compared to thick soils composed of rocks which easily breakdown eg limestone.
What are the inputs of the soil system?
- precipitation and ground water flow
- atmospheric gases, e.g. oxygen, nitrogen, and carbon dioxide
- mineral nutrients from weathered rock
- organic material from dead organisms
- Solar energy
What are the outputs of the soil system?
- water loss through transpiration and evaporation
- Nutrients taken by plants
- Mineral nutrients, lost through leaching an eluviation
- loss of soil by erosion or slope movement
- Permanent loss of nutrients due to clearing of vegetation including harvesting
What causes horizons or soil profiles?
Due to processes that organise soil components
- weathering of bedrock
- leaching
- accumulation of minerals where groundwater conditions cause precipitation
- eluviation (movement of dissolved or suspended mineral matter)
- breakdown or organic matter into humus
What are zonal soils?
Refers to a strong, old, well developed soil with distinct horizons.
What are azonal soils?
Azonal soils are the soils that lack well developed horizons because of immaturity or other factors that have prevented their development;
Usually found in steep slopes or retreating coastlines.
They have characteristics of their parent rock.
The opposite to zonal soils.
What is horizon O?
Represents a surface layer consisting of leaf litter and loose organic material. Is home to bacteria, fungi, insects, and other organisms which breakdown material to form humus.
What are soils and how do they form?
Soils form at the intersection between the geosphere atmosphere, hydrosphere, and biosphere also known as the regolith.
Six factors contribute to the production of soil;
1 the parent rock material present
2 the climate
3 the topography
4 organisms 
5 passage of time
6 human activity
What is the composition of a typical, mature soil?
45%, air and water
40% mineral material
10% organic
5% biotic
How can Human activity affect soil?
- Addition of fertilisers and mineral supplements changes chemical composition.
- deforestation and harvesting removes nutrients and organic matter impacting soil quality and structure
- Urbanisation changes drainage patterns in a landscape isolating soils from biotic influences
- Excessive irrigation can wash, soluble nutrients out of surface layers or even strip them from landscape altogether.

How do organisms affect soil?
They build up and store nutrients so when they are decomposed, this nutrients is released into the soil eventually creating humus.
Burrowing animals and insects are also important as they mix water and air through the soil, redistributing minerals and organic components.

How does climate affect soils?
Climate affects temperatures, water air and organic content which are some of the fundamental components of soil.
c. Intuencis a narc and animal life supported in an area.
Some climates with soil-climate correlations include
• Humid Tropical Regions
• Arid Regions
• Temperate Regions
• Cold climates with little rainfall
What are conditions of tropical soils
Humid Tropical Regions - heavy rainfall and high temperatures produce rapid chemical weathering and luxuriant plant growth. Soils may have a deep profile, with weathering extending to 30-50 metres below the surface. Strong leaching and eluviation remove most nutrients from the soil, as well as all but the most stable minerals. Soils in these regions generally have a low fertility.
What are soil components of arid regions?
• Arid Regions - regardless of temperature, the lack of water in the environment limits the degree of both chemical and physical weathering and hence the formation of regolith. Physical erosion is dominated by windblown sand and intermittent flash floods. There is limited vegetation growth and hence little humus, so soils are poorly developed.
What are cellular components of temperate regions?
• Temperate Regions - physical and chemical weathering produce a wide variety of soil profile types.
What are soil conditions of cold climates?
• Cold Climates with Moderate Rainfall - low temperatures mean chemical weathering is slow, with little alteration of parent minerals. Physical weathering is dominated by frost shattering. Little vegetation growth, so there is limited soil development.
Parent material
The breakdowns and modification of local geological substrates make up soil chemical and mineral composition.
