Causes of Soil Degradation Flashcards
What is soil degradation?
- Loss of soil quality:
Loss of biological and chemical components, loss of nutrients, physical integrity, pollution. - Loss of soil quantity:
Soil erosion, loss of volume by oxidation of peat.
What does soil erosion preferentially lose?
Preferentially loses, clay, organic matter
Where are large rates of erosion happening?
Nigeria, India, China
What was the average rate of soil erosion in China in 2010?
9.4 tonnes per hectare per year
How much of the worlds arable topsoil has been lost to erosion?
Nearly 33% in the last 40 years
How much fertile soil do we lose every year?
24 billion tonnes
What is the relationship between the rate of nutrient loss and natural replenishment?
The rates of nutrient loss by leaching, removal of crops and soil erosion exceeds the rate of natural replenishment of nutrients
What are the causes of soil degredation?
- Tillage
- Overgrazing
- Monocultures / crop type
- Chemical fertilisers
- Bare soil
- Crops with small roots
- Reduced soil organic matter
- Compaction
- Climate change
How much soil compaction is caused by the first pass of machinery?
85-90%
What is wrong with tilling?
Soil disturbance, disturbs SOC stocks and nutrients
Fragments created by tilling are less stable than naturally forming aggregates.
How much higher are rates of erosion from ploughed fields?
Erosion rates from ploughed fields ~10-100 times greater than rates od soil formation.
What issues do monocultures/crop type cause?
- Monocultures are vulnerable to pests,disease and extremes of weather, nutrient losses
- Modern crops store less carbon in roots, associated with soil degeneration and erosion.
What are the worst crops for soil loss?
Root crops - soil loss of ~3.5 tonnes per hectare per year
particularly sugar beet
How can climate change affect soil?
More extreme weather can lead to erosion and salinisation.
High rainfall causes increased soil acidity.
Highly leached soils are rich in aluminium and iron oxides which strongly sorb phosphorus, making it unavailable for plants.
What is wrong with highly acidic soils?
Aluminium becomes soluble, it is toxic for plant roots.
Toxic concentrations of Fe, Al, Mn and other trace metals
Very low in available and exchangeable nutrients N, P, Ca, Mg
