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5.1 Introduction to soil systems - Coggle Diagram
5.1 Introduction to soil systems
Soil is a complex ecosystem
Minerals (Rocks), is the skeleton of soil.
Organic material (Humus), containing the nutrients and gives the dark colour.
Gases (Air), for respiration of soil organisms
Liquids (Water)
Many plants and animals (and micro-organisms)
Importance of Soil
Responsible for all food production
Provides all nutrients for producers
Habitat for many organisms
Filters water
Recycling nutrients (decomposers and detritivores)
Chemical reactions
“Too many people have lost sight of the fact that productive soil is essential to the production of food”:
Hugh Hammond Bennett was a pioneer in the field of soil conservation.
He was convinced that soil erosion was a serious problem facing the planet.
Reduces areas in which crops can be grown.
Soil horizons (layers)
O - (Organic) Freshly fallen leaves, twigs, animal waste, fungi
A- Mixture of partially decomposed organic matter
B- (Subsoil) Nutrients leached from A “Plant Roots”
C- (Parent Material) largely inorganic material
R-hard bedrock
How Does Soil Form
Very slow process
Weathering of rock (mechanical)
Deposition of sediments by erosion (mechanical)
Decomposition of organic matter (chemical)
Soil Particles:
Clay < 0.002mm in diameter
Silt 0.002 – 0.05 mm in diameter
Sand 0.05 – 2 mm in diameter
Soil Texture is determined by the relative amount of the different types and sizes of mineral particles
(If fairly equal portions of each are present it is said to be a loam/Soil texture affects fertility and primary productivity)
Determine Soil Texture
Rub soil between finger: Sand falls apart; Silt feels slippery and holds together; Clay feels thick and stick and forms shapes
Sieve screen
Soil Permeability:
Porosity – The space between the particles
Permeability – The ease at which gases and liquids can pass through the soil
Clay soils – High porosity (macropores), low permeability, high nutrients but inaccessible.
Sandy soils – High porosity (micropores), high permeability, high leaching
Loam soils – Best of both, ideal for agriculture
Translocation: Water carries particles up or down the layers
In hot, dry climates precipitation is less that evaporation
This means that water moves up through the layers.
As water evaporates it leaves the minerals behind, this is called salinization.
Can also happen with irrigation.
In colder, wet climates water flows down into the soil, dissolving minerals and transporting them downwards.
This is known as leaching.
Acidification of Soil
Acid precipitation increases acidity near urban areas
Clay soils often have high acidity due to absorption of water
Causes leaching of potassium, magnesium and ammonium
Causes aluminum and iron to become more available to plants which are toxic
Soil Sustainability
Fertile soil is a non-renewable resources
Fertile soil has enough nutrients for healthy growth (N,P,K)
Nutrients are leached from soil by water
Nutrients are lost when crops are harvested
Replace nutrients with fertilizers
More sustainable method of replacing nutrients is by crop rotation, planting legumes and using organic fertilizers