Soil Erosion
Wearing away of fertile topsoil by wind and water
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Deforestation and overgrazing exposes soil
Farming practices such as ploughing downslope can lead to rilling
Relief as soil more likely to be washed away on steep slopes
Climate as water erosion more likely after heavy rainfall and wind erosion more likely in very dry conditions
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Soil becomes less fertile as nutrients are removed
Soil’s ability to retain water reduced
Can cause rills and gullies that make the cultivation of paddocks impossible
Results in lower yields and higher production costs
Around 10 million hectares of land abandoned each year due to lack of crop productivity
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Afforestation to allow roots to stabilise soil and return leaf litter nutrients
Fertilisers added to soils to improve nutrient content
Rotate crops to allow soil to recover before planting again
Planting natural windbreaks, such as hedges
Ploughing across, rather than down, slopes
Terracing on steep slopes
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Waterlogging
When pores between soil particles fill with stagnant water
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impermeable soils that have few pores, such as clay
Heavy rainfall in areas where rates exceed evapotranspiration
Over-irrigation
Hard-pans can stop percolation and create an impermeable layer
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Gleying leads to soil infertility
Rotting of plant roots
Weeds outgrow crops as can survive waterlogged conditions better
Reduced soil temperature leading to slower crop growth
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Improving field drainage
Sustainable irrigation systems
Adding sand to clay soils to increase pore spaces
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Salinisation
Accumulation of salt within soil
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Natural causes
- High temperatures and low precipitation lead to high rates of evaporation so that salts left on ground surface
- Sea-level rise can draw salt up into soil in coastal areas
Human causes
- Over-abstraction of groundwater for irrigation leads to saltwater intrusion
- Over-irrigation of water containing dissolved salts
- Fertilisers containing salts left in soil
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3000-6000 ppm of salt can be toxic to plants
Decreases osmotic potential of soil so plants can’t get required water
Pea and bean crops particularly vulnerable
Salinisation in San Joaquin Valley, California, projected to cost the state $1-1.5 billion
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Drip-irrigation and soil moisture monitoring
Selection of deep-rooted crops to increase water retention
Soil flushing with water (although this moves problem elsewhere)
Using fertilisers with low salt content
Strategies to avoid waterlogging (as above)
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Structural Deterioration
Pore spaces are lost as the structure of the soil is squeezed or collapses
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Removal of vegetation so that roots no longer there to support the soil
Soil compaction from heavy farm machinery or livestock trampling
Salt in soil causes clumping together of clay particles
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Lack of space in soil for infiltration of water to occur so crops dry out quickly
Plant roots unable to grow through compacted soil as they need air pockets to survive
Farmers unable to till and plough the soil if it is too compacted
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Avoiding use of heavy machinery
Move livestock around to avoid compaction
Introducing more organic matter into the soil to encourage the soil to aggregate together to increase number of pore spaces
Strategies to avoid salinisation (as above)
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