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5.8 Soil degradation and conservation - Coggle Diagram
5.8 Soil degradation and conservation
Soil ecosystems change through succession.
Fertile soil contains a community of organisms that work to maintain functioning nutrient cycles.
These communities help keep the soil resistant to erosion.
Two main types of process can give rise to soil degradation;
Generally commercial industrialised food production systems reduce soil fertility more than small-scale subsistence farming.
Processes that take away the soil (erosion).
Occurs when there is no or little vegetation on the soil.
Wind and water.
Processes that make the soil less suitable for use.
Loss of chemicals/nutrients (leaching)
Addition of chemicals (pollution)
Human activities that lead to soil degradation
Deforestation
Unsustainable agriculture
Overcropping
Overgrazing
Urbanisation
Overgrazing:
too many animals grazing in the same area.
plants cannot recover
leads to bare patches with no plants
if plants do survive their roots never develop properly
Case study: Sahel in Africa (just south of the Sahara):
1970s and 1980s
wealth determined by the number of cattle a man owns
lead to very high stocking
exacerbated by drought
wind erosion
cattle died
mass famine
Over cropping:
depletes soil nutrients
makes the soil friable (dry and susceptible to wind erosion)
Nutrients are not restored
Increased risk of crop failure then wind erosion
Case study:" dust bowl" - 1930s American Mid West:
over use of land
wind erosion
soil and dust moved many thousands of km
Deforestation: Removal of vegetation leads to exposure of soil.
Tropical rainforests are in areas with very high precipitation.
Massive amounts of water erosion
Leaves slow down rain, roots bind the soil.
Unsustainable agricultural techniques:
Techniques that can be applied over a long period of time without decrease in productivity or increased fertilisers.
Total removal of crops (leaves bare soil).
Growing crops in rows with bare soil in between (Especially bad if rows are in the direction of the slope)
Ploughing in the direction of slope makes channels for the water to flow down.
Excessive use of pesticides (toxification).
Irrigation – water evaporates leaving behind a hard, salty layer (salinization).
Monocultures mean the same nutrients are depleted.
Urbanisation:
More people now live in cities than in rural areas.
Increased run off may lead to extra erosion down stream.
Many major cities expanded from settlements that were based on agriculture, therefore they are expanding into prime agricultural land.
Types of soil erosion: Leaves deflect heavy rain, roots hold soil together and humus absorbs large quantities of water.
Gullying: Channels develop on hillsides following rainfall. Over time they get deeper and deeper.
Wind erosion: Drier soils have the top layers consistently removed.
Sheet wash: Large areas of surface soil are washed away during heaving rain.
Can include landslides
Solutions:
Addition of soil conditioners (lime, organic material)
Wind reduction
il conserving cultivation techniques (Cover crops, terracing, ploughing, contour farming)
Improved irrigation (trickle flow)
Improved irrigation (trickle flow)