Soil degradation and Conservation

soil degradation and processes

the physical, chemical and biological decline in soil quality. processes: take away soil (erosion) = no vegetation or make soil less suitable for use= chemicals

• Leaves deflect heavy rain, roots hold soil together and humus absorbs large quantities of water.

soil erosion types

• sheet wash: large areas washed away (landslides)

• gullying: channels that develop on hillsides, deepen over time

  • wind erosion: wins continually remove top layer of dry soils

erosion

Soil particles can be transported from one place to another by either water or wind. Erosion typically removes the fertile topsoil= leads to a reduction in water retention capacity

human activities that lead to degradation

overgrazing, overcropping, deforestation, unsustainable agriculture and urbanization

overgrazing

too many animals in the same area, leaves bare patches of soil that then erode away. 

overcropping

depletes the soil of nutrients making soil friable (dry and susceptible to wind erosion) and nutrients are not restored = increased risk of crop failure then wind erosion.

deforestation

removal of forest. If all vegetation is removed soil is vulnerable to erosion

urbanization

expanse of cities and increase in impervious surfaces = increased **run-off** may lead to extra erosion downstream

overgrazing case study

Sahel in Africa in 1970sand 1980s - wealth determined by the number of cattle a man owns which lead to a very high stocking = decrease in vegetation made worse by drought = wind erosion and cattle died = mass famine

overcropping case study

Dust Bowl - 1930s American Mid West

overuse of land = wind erosion = soil and dust moved many thousands of kilometers

unsustainable agriculture techniques

• total removal of crops after harvest

• ploughing in direction of slope - allows water to run off

• excessive pesticides use (toxification)

• irrigation that leads to salinization

  • monoculture depletes specific soil nutrients making crop failure more likely

soil conservation

* addition of soil conditioners
* wind reduction
* soil conserving cultivation techniques
* improved irrigation technqiues
* stop ploughing marginal lands
* crop rotation

addition of soil conditioners

* lime to increase pH.
* Soil becomes acidic through harvesting crops that removes nutrients, acid rain & leaching
* Organic matter improves texture, aeration & fertility

wind reduction

* planting trees.


* alternating crop height.

soil conserving cultivation techniques

* Cover crops & strip cultivation


* Reduce/zero tillage to improve soil structure
* Ploughing to improve drainage may increase erosion
* Contour farming and terracing 

improved irrigation techniques

Drip irrigation -  taken in by roots prior to evaporation avoids salination

stop ploughing marginal lands

* Thin topsoil and low rainfall zones are at greater risk of erosion


* Zero-tillage techniques are useful

crop rotation

* Legumes add nitrogen to the soil


* Repeated monoculture may cause disease 
* Fallow - some years where nothing is grown allows soil structure and fertility to improve

acidification

Increase in hydrogen ion concentration = lowers pH = aluminium becomes more soluble = prevents root growth = restricting access to water and nutrients

Causes: acid deposition, leaching and removal of nutrients from the soil and use of ammonium based fertilizers.

soil compaction

occurs when air and water pushed out of soil making it more dense. Worse with wet soil as less able to withstand compression = restricts root movement, water infiltration, drainage and air circulation. Restricted roots = can’t intake sufficient water or nutrients=less plant growth and lower yields.