IB Environmental Systems and Societies

1. Topic 5
Soil systems and terrestrial food
production systems and societies
5.1 The Soil System

2. Soils
• The interface between:
– Atmosphere
– Lithosphere
– Biosphere
– Hydrosphere
• Comprised of:
– Regolith (weathered bedrock)
– Organic matter (living and non-living)
– Air
– Water
• Exist in all 3 states
– Solid (organic and inorganic matter)
– Liquid (water from precipitation, seepage and groundwater)
– Gas (volatiles in atmosphere and within pores)
• Soils take so long to develop that they are generally considered to be
a non-renewable resource
http://www.youtube.com/https://www.youtube.com/watch?v=iGfco7kNzJA?v=a1_WPMu0ZiI

3. The Soil System
• Any soil is an open system (there are inputs and outputs of matter and
energy)
• Inputs
– Organic matter (e.g. decomposing leaf litter)
– Inorganic matter (e.g. water)
– Energy (sunlight, heat)
• Outputs
– Uptake of all inputs by plants
– Radiation of heat from soil surfaces
– Erosion
• Storages
– Organic matter
– Nutrients
– Organisms
– Minerals
– Air
– Water
• Transformations (Processes)
– Weathering of minerals
Soils are ecosystems – biotic
and abiotic factors occurring in
a self-supporting system

4. Soil Profiles
Horizon Characteristics
Organic horizon (O) undecomposed litter
partly decomposed litter
well-decomposed humus
Mixed mineral-
organic horizon (A)
humus
ploughed
gleyed or waterlogged
Eluvial or leached
horizon (E)
strongly leached
weakly leached
Illuvial or deposited
horizon (B)
iron deposits
clay deposits
humus deposits
Bedrock or parent
material (C/R)
rock
unconsolidated loose deposits
The boundaries between horizons are often blurred due to earthworm activity
soil horizons

5. How Are Soils Formed?
• They are considered to be open systems in steady-state
equilibrium
• The main processes of formation are:
– Weathering
– Translocation (movement of substances) *
– Organic changes (largely near the surface)
– Gleying (waterlogging)
• At the surface, humus is created (humification) and
eventually decomposed completely (mineralisation) – they
always occur together
• Human activity is having severe effects on soil formation
* Translocation usually occurs downwards due to the movement of water and dissolved
substances. However in arid environments movement is upwards due to evaporation
soil formation animation

6. Using Soils
• The main human use of soils is for
cultivation (also peat extraction to a
lesser extent)
• For cultivation, the ideal soil has a
good balance between water-
retention and drainage (porosity)
and aeration
• These properties are based on soil
texture
• Texture depends on the proportions
of different sized particles
(sand/silt/clay)
• The ideal balance of particle size is
achieved in loamy soils
http://www.youtube.com/watch?v=7V5qUusgYLw

7. Porosity vs Surface Area
• Pore size determines the rate of drainage of water and
how easily it is aerated
• Particle size/ surface area determines how easily water
and dissolved nutrients are retained (against gravity)
– Light soils (> 80% sand) – coarse texture, easily drained;
low primary productivity
– Heavy soils (> 25% clay) – fine texture, small pores (<
0.001mm), water and nutrient retentive, chemically active,
not easily worked (ploughed)*; low primary productivity
– Medium soils – somewhere in between (loam); high
primary productivity
Ploughing a clay-rich soil

8. Soil Structure

10. Porosity vs Surface Area
• A variety of pore sizes is required to allow root
growth, water drainage, aeration and water
storage
– Pores > 0.1 mm are needed for root growth
– Pores < 0.05 mm are needed for good water
storage
• Overall soil structure depends on:
– Soil texture (see the triangle)
– Amount of dead organic matter
– Earthworm activity