Soil Degradation and Conservation Flashcards
Name 4 activities that can lead to soil degradation
- overgrazing
- deforestation
- unsustainable land practises
- urbanisation
When does overgrazing occur and what is the result?
- overgrazing occurs when too many animals graze in the same area
- leaves bare patches where roots no longer hold the soil together
- when combined w action of rain + wind, bare patches become bigger + soil is removed from area
Where did overgrazing happen on a large scale in the 1970s and 80s?
- Sahel
- In many African countries, wealth of a man measured by the no. of cattle he has
- this leads to v high stocking levels + overgrazing
- exacerbated in 1970-80s when long dry period strongly reduced growth of vegetation, which was subsequently eaten by cattle
- soil particles no longer kept in place by roots + blown away
- resulted in death of most cattle + ultimately a terrible famine
Why is overcropping so bad for soil?
- depletes soil nutrients
- makes soil friable (dry + susceptible to wind erosion)
- reduces soil fertility as no nutrients returned to soil
- if crop fails then soil surface again becomes susceptible for erosion
- e.g Dust Bowl, American Mid West, 1930s
Why is deforestation so bad for soil?
- the more vegetation removed, the more the soil will be prone to erosion
- esp. due to water
- leaves of forests both deflect + slow down progress of rain drops
- helps to stop them explosively removing particles
- roots systems help bind soil together + give stability + absorb large quantities of water from soil directly
- absorbed water returned to atmosphere via transpiration
Name 4 unsustainable agricultural techniques that result in soil degradation
- total removal of crops after harvest, leaving soil open to erosion
- excessive use of pesticides leading to toxification of soil
- plowing in direction of slope, creating channels for rainwater + soil to flow down
- monocultures mean same nutrients depleted from soil, reducing its fertility
What are the 3 major processes of soil erosion?
SHEET WASH
- large areas of surface soil washed away in storms + landslides
GULLYING
- channels develop on hillsides following rainfall, becoming deeper over time
WIND EROSION
- on drier soils high winds continually remove the surface layer
How can the addition of soil conditioners help conserve the soil?
- soil conditioners inc. lime
- for centuries farmers have added lime to counter acidification
- lime also helps clay particles stick together so they act more like sand particles
- large particles created = more free draining + trap more air
- so help improve decomposition by microorganisms
Why does soil become acidic?
- Acid rain
- Breakdown of organic matter creates co2 through respiration, that dissolves in soil water creating carbonic acid
- Nitrification of ammonium ions to nitrates increases acidity
- removal of basic ions through leaching
How can wind reduction methods help conserve soil?
Effect of wind can be reduced by:
- planting trees // bushes between fields
- alternating low + high crops in adjacent fields
- building fences
Name 4 soil conserving cultivation techniques
> Fast growing crops to cover the soil between rows of main crops to keep soil particles in place
> Terracing reduces steepness of slopes by replacing slope w series of horizontal terraces, separated by walls eg. Asian wet rice fields
> Plowing temporarily increases drainage , but evidence that plowing is bad for soil structure + microbial activity
> Contour farming is plowing + cultivating perpendicular to slope so trapping soil + water
Why is soil erosion a good thing is natural systems?
- Ends up in water courses, providing essential minerals + nutrients for aquatic ecosystems
- Eroded upland soils will wash into valleys creating deep fertile soils
