1. Introduction to Soil Systems 5.1
I Am Soil
Starter:
What is soil?
Why is soil so important?
Where does soil come from?

2. Applications and Skills
Outline the transfers, transformations, inputs, outputs, flows, and storages within soil systems
Explain how soil can be viewed as an ecosystem
Compare and Contrast the structure and properties of sand, clay, and loam soils, with reference to a soil texture diagram, including their effect on primary productivity

3. Soil is a complex ecosystem
Minerals (Rocks)
Organic material (Humus)
Gases (Air)
Liquids (Water)
The exact mix of these four portions which give soil its characteristic.
Many plants and animals (and micro-organisms)

4. Why is Soil Important?
Ultimately responsible for all the food we consume
Recycling nutrients (home wo many decomposers and detritivores) so that chemical cycles can occur
Provides all nutrients for producers
Habitat for many organisms
Filters water

5. What is Soil Made Of? Rock Particles: from parent rock material
Made of gravel, sand, silt, clay, and chalk
Contains minerals
Humus: Organic matter made from the decomposition of living things
Results in nutrients and minerals returning to soil
Absorbs and retains water
Water: held in spaces between soil
Dissolves minerals and allows movement through soil and uptake by plants (rapid movement of mineral salts can lead to salinzation)
Too much water can lead to anoxic conditions and acidification

6. What is Soil Made Of? Air: held in soil grains
Well aerated soil provides oxygen for soil organisms and plant roots
Soil Organisms: mostly invertebrates but can be things such as moles
Break down large particles (detritivores)
Decompose—recycling minerals and nutrients
Mix and aerate soil (eg moles, prairie dogs, naked mole rats)

7. How Does Soil Form?

8. How Does Soil Form? Very Slow Process Weathering of rock (mechanical)
Deposition of sediments by erosion (mechanical)
Decomposition of organic matter (chemical)

9. Soil System Components
Storages
Organic matter, organisms, minerals, air and water
Transfers within the soil
Biological mixing, translocation (movement of soil particles in suspension) and leaching (minerals dissolved in water move through soil)
Inputs
Organic material including leaf litter and inorganic matter from parent material, precipitation and energy
Outputs
Uptake by plants and soil erosion
Transformations
Decomposition, weathering, and nutrient cycling
Construct a Systems Diagram with the above data

10. Systems Diagram

11. Systems Diagram Soil Minerals Weathering Air Water Leaching Biological
Nutrient
Cycling
Biological
Mixing
Inorganic
Matter
Respiration
Soil
Biological
Mixing
Biological Mixing
Nutrient Cycling
Plant uptake
Biological
Mixing
Nutrients
Organisms
Decomposition
Decomposition
Organic Matter

12. Soil System Food Web

13. Nitrogen Cycle Review

14. Carbon Cycle Review

15. Soil Horizons (Layers/Profiles)
O – (Organic) Ecosystem litter, organic matter (humus), soil organisms (bacteria, fungus, etc)
A – (Topsoil) Mixture of partially decomposed organic matter
E – (Subsurface) depleted organic matter & clay
B – (Subsoil) Nutrients leached, clay and minerals such as iron & aluminum compounds
C – (parent material) loose rocks
R – Bedrock

16. Mosaic
of closely
packed
pebbles,
boulders
Alkaline,
dark,
and rich
in humus
Weak humus-
mineral mixture
Dry, brown to
reddish-brown, with
variable accumulations
of clay, calcium
carbonate, and
soluble salts
Clay,
calcium
compounds
Desert Soil
(hot, dry climate)
Grassland Soil
(semiarid climate)

17. Tropical Rain Forest Soil (humid, tropical climate)
Forest litter
leaf mold
Acid litter
and humus
Acidic
light-
colored
humus
Humus-mineral
mixture
Light-colored
and acidic
Light, grayish-
brown, silt loam
Iron and
aluminum
compounds
mixed with
clay
Dark brown
Firm clay
Humus and
iron and
aluminum
compounds
Tropical Rain Forest Soil
(humid, tropical climate)
Deciduous Forest Soil
(humid, mild climate)
Coniferous Forest Soil
(humid, cold climate)

18. Soil Particles Clay < 0.002mm in diameter
Silt – 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

20. Determining Soil Texture
Rub soil between finger:
Sandy soils fall apart easily
Silty soils feel slippery and hold together
Clay soils feel thick and sticky, can be formed into shapes

21. Determining Soil Texture
To determine the soil proportions you can dry out a soil sample and pass through a meh of different sizes (2mm, then 0.05 mm then mm)

22. Soil Permeability
Permeability - The rate at which air and water can flow through the layers
Porosity – The space between the particles
Permeability – The ease at which gases and liquids can pass through the soil

23. Soil Permeability
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

24. This is known as leaching.
Water carries particles up or down the layers - translocation
In colder, wet climates water flows down into the soil, dissolving minerals and transporting them downwards.
This is known as leaching.
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.

25. Water Holding Capacity
Soil Texture
Nutrient Capacity
Infiltration
Water Holding Capacity
Aeration
Workability
Clay
Good
Poor
Silt
Medium
Sand

26. 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

27. 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