R2102 1.1 Describe the formation of typical mineral soils Flashcards
What is soil texture?
Describes the relative quantities of sand, silt and clay particles in a soil
What is soil structure?
Describes the arrangement of soil particles and the spaces between them
What does a naturally fertile soil provide for plants? (4)
- Water
- Air (oxygen)
- Nutrients
- Anchorage
Types of rock (3)
- Igneous e.g. Granite
- Sedimentary rock e.g. Sandstone
- Metamorphic rock e.g. Slate
Types of physical weathering processes (5)
- Water - moving water abrading or scouring rocks
- Wind - abrasive particles ‘sand blasting’ exposed rock
- Heat - Sun, heating and cooling of rocks lead to surfaces breaking away
- Frost - water freezes and expands
- Glacier - enormous forces pluck rock away and large rocks embedded in the ice scour away the rock with which in comes into contact
Mainly occurs on exposed rock - not that protected by thick soil layer
Types of physical weathering processes (5)
- Water - moving water abrading or scouring rocks
- Wind - abrasive particles ‘sand blasting’ exposed rock
- Heat - Sun, heating and cooling of rocks lead to surfaces breaking away
- Frost - water freezes and expands
- Glacier - enormous forces pluck rock away and large rocks embedded in the ice scour away the rock with which in comes into contact
Mainly occurs on exposed rock - not that protected by thick soil layer
Types of chemical weathering (1)
- Carbonic acid. As carbon dioxide from the air dissolves in rain it forms Carbonic acid which dissolves the Calicum Carbonate in chalk and limestone
Types of biological weathering (3)?
- Combination of physical (mechanical) and chemical weathering
- Mosses and lichens on rock produce large quantites of carbonic acid
- Roots penetrating gaps in rocks in search of water
What is parent rock?
Rock from which the soil is made
What is weathering?
The breakdown of rock
What is erosion?
The movement of rock fragments and soil broken down by weathering
Four processes that help for particular soils
- Additions - from outside sources such as organic matter from leaves, dust from atmosphere or soluble salts from groundwater
- Losses - material leached out to groundwater, erosion of surface material
- Transformation - Soil constituents changing from one form to another e.g. by mineral weathering and breakdown of organic matter
- Translocation - Movement of organic and inorganic matter from one horizon to another. Washed downwards by water or moved by soil organisms such as earthworms
Erosion processes (4)
- Gravity - fragments on loss slopes travel downhill e.g. scree
- Water e.g. Alluvial soil - layers of sand and silt left behind with organic matter in flood planes
- Wind - Particles carried by wind, leading to large areas of sandy materials which form loess soils
- Glaciers - soils left by glaciers are known as boulder-clay
What is the soil horizon?
A specific layer in the soil seen by digging a soil pit
What is a soil profile?
Vertical sections through the soil. They show the different layers
What are the main layers in a soil profile (4)
- Horizon O - organic layer
- Horizon A - topsoil
- Horizon B - Subsoil
- Horizon C - Parent material
What is in the organic layer (Horizon O)?
Layer of fresh plant litter which has yet to be incorporated into the soil (sometimes know as Horizon AO)
What is the topsoil (Horizon A) (6)?
- Material at top of soil profile
- Usually dark brown or black in colour
- Contains greatest proportion of orgainic matter
- Most affected by the actions of living things
- Most roots found in this layer, abundant plant and animal life
- Typically 10-40cm deep
What is subsoil (Horizon B)(3)?
- Layer below the cultivated layer
- Lighter in colour because of low organic matter level. Colour depends greatly on the chemicals coating the particles
- Material transported down from topsoil may accumulate here, finer particles washed down.
- Reduced biological activity lead to poorer air and water movement
What is the parent material (Horizon C)
Material from which the soil has developed and generally consists of almost unaltered rock. The original nature of the rock can be seen.
