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soil .pdf



Original filename: soil.pdf
Author: Jack Whelan

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Soil Composition

Mineral: 45%
Organic: 5%
Air: 25%
Water: 25%

Mineral Matter:
Stones, Sand, Silt and Clay
Broken down rock
Particle size : Parent material
Some are soluble -> Plant food

Organic Matter:
Plant litter
Micro-organisms
Worms, mites, slugs
Decay to form humus
Worms churn into soil

Air + Water:
In pores
Essential for plant growth
Important for organisms
Water contains dissolved minerals

Soil Characteristics

Texture
Sand/gritty > Silt/silky > Clay/sticky
Ability to retain water + Nutrients
Ease of root penetration

Structure
Clumps of peds
Crumb (+Drainage+Air)
Platy (-Impede roots-Hold up water)
Blocky (-Few pores)

pH
3 > 7 > 10
Effects what can grow in it

Humus
Dark brown/Black
Improve structure

Moisture
Plants receive nutrients through water
Water disperses nutrients
Texture + Structure influence moisture
Sandy > Dry
Clay + Silt > Wet + can become waterlogged
Loam > Well drained/moist/fertile
Bedrock > Permeable/Impermeable

Colour
Brown + Black > High humus
Grey > Leached + Infertile
Red > Iron oxide

Factors Effecting Soil Formation
Climate
Temperature
Precipitation
Hot > Deep soil (Weathering)
Cold > Angular particles (Freeze thaw)
Wet > Leaching / Water logging
Dry > Upward movement of groundwater (Salinisation/Calcification)
Parent Material
Sandstone > Sandy + Free draining
Shale > Clay + Badly drained
Limestone > Thin, dry + poorly developed
Igneous + Metamorphic > Weather slowly and tend to be acidic
Topography
Relief, Altitude and Aspect
Flat + Upland > Waterlogged/Leached
Upland > Cooler --> Builds up as peat instead of humus
South-Facing > Warmer + Dryer than south-facing
Soil Organisms
Bind soil particles
Break compacted soil
Time
400y/cm

Processes of Soil Formation
Weathering + Erosion
Breaks down bedrock to form parent material
Mechanical weathering: Freeze thaw + Exfoliation
Carbonation
Hydrolysis - Turns feldspar in granite to kaolin clay
Oxidation
Humification
Hot -> Temperate
Fastest in warmer weather
Leaching
Podzolisation
Extreme leaching
Water going through the top layer of humus leads it to become acidic
Erodes all mineral matter + deposits on the b horizon
Forms hard pan
Laterisation
Severe leaching (Tropical)
Rapid Chemical weathering > Deep soil
Latosol (Red) formation
Salinisation
Accumulation of soluble salts close to the surface
Hot climates
High levels of evaporation leads salty groundwater to the surface where it leaves the layer of
salt behind as a toxic crust
Can also be caused by irrigation (by rising salts to surface)
Calcification
Accumulation of calcium carbonate near the surface
Grassland
Evaporation > rainfall => calc. drawn upwards
Capillary action
Calc. Carbonate builds up in A horizon creating a soil which is rich in nutrients + ideal for
grass growth


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