Soil problems and management

Are soils a finite resource?

Are soils a finite resource?

Yes, as they take thousands of years to become sufficiently deep and mature for agriculture.

What statistics about soil erosion were states at the World Economic Forum in 2012?

- Soil is being lost at 10-40 times the rate at which it can be replenished
- Food production would decline by 30% in the next 30-50 years without soil management

What are the four major problems with soil?

- Soil erosion
- Soil salinisation
- Waterlogging
- Structural degradation

What is the definition of soil erosion?

The loss of topsoil through natural forces such as wind and rain, or human activities such as deforestation and tillage.

What part of the soil is most susceptible to erosion and why is this an issue?

Topsoil is most commonly eroded, which is typically the most fertile layer and therefore most important for agriculture.

What are the two types of natural soil erosion and what features can they form within the soil?

- Wind erosion -> common in arid regions/regions experiencing seasonal rainfall
- Water erosion -> common in areas of high rainfall
Wind and water erosion can form rills and gullies if they are concentrated in a specific area of soil.

How much fertile soil is estimated to be lost per year due to water erosion?

75 billion tonnes of topsoil annually

What are gullies?

Deep channels cut into the soil by running water.

What are rills?

Shallow channels cut into the soil by running water.

What human activity can accelerate natural soil erosion?

Poor land management (often due to population pressure) can accelerate soil erosion by allowing:
- overgrazing
- over-cultivation
- deforestation

What regions of the world is soil erosion due to human activity most prevalent?

- LICs and NEEs, as their economies tend to rely on agriculture and many farmers lack proper equipment/education.
- However, it is also an issue in some HICs due to extreme commercial farming.

What are the impacts of soil erosion (five impacts)?

- Reduced crop yields
- Loss of seedlings/seeds and fertilisers
- Damage to water quality due to sedimentation
- Deposition of sediment onto roads/drains (increased flood risk)
- Young plants being sandblasted (wind erosion)

What is the most effective way to manage soil erosion?

- The provision of surface cover through afforestation, which stabilises the soil and protects it from the impact of wind and rain.
- Farmers can create contour banks which restrict the downhill flow of water.

How can the erosion of soil by water be managed (four strategies)?

- Installing and maintaining field drains and ditches
- Use cover crops and contour ploughing (on slopes) where possible to stop the formation of ridges and gulleys
- Use manure to stabilise the soil
- Reduce the amount of water running off roads

How can the erosion of soil by wind be managed (three strategies)?

- Increase plant cover to approx. 50%
- Plant lines of trees or hedgerows to reduce evaporation and wind erosion by 20%
- Increase soil cohesion by adding organic matter

What is waterlogging?

When the water table rises to the point of soil saturation and there is insufficient oxygen in the pore spaces for plant roots to respire adequately. This causes root tissue to die.

What are the main causes of waterlogging and where is it most common?

- Waterlogging can be caused by heavy rainfall, impermeable bedrock, high runoff ad irrigation
- It is most common in countries with heavy rainfall or a high water table, e.g., Egypt

How can waterlogging be managed?

- Growing crops tolerant to waterlogged soils
- Planting crops earlier so they are mature enough to withstand wet conditions
- Drainage channels

What is salinisation?

The accumulation of salts in the soil. As water evaporates, any dissolved salts can be left behind.

How does salinisation affect crops?

- At salt concentrations between 3000-6000(+)ppm most plants become infertile
- Only salt-tolerant crops such as cotton are generally able to withstand (extreme) salinisation

What are some natural causes of salinisation?

- Low precipitation
- High temperatures leading to high levels of evaporation
- Sea level change

What are some human causes of salinisation?

- Over-abstraction of groundwater
- Irrigation

How can salinisation be managed?

- 'Flush' the soil with lots of water (although this just salinates groundwater/rivers)
- Lower the water table by planting vegetation, installing drainage and extracting ground water

What are three examples of soil structures?

- Granular and crumb structures -> individual particles grouped in nearly spherical grains, water drains easily through these soils and they are common in A horizons
- Blocky structures -> soil particles that cling together in square/angular blocks, with large blocks showing that the soil resists penetration.. often found in the lower B horizon
- Prismatic and columnar structures -> soil particles in vertical columns separated by cracks, water does not circulate well

What is structural deterioration?

- Pore spaces in the soil are lost
- Soil structure/horizons become undefined and compacted

What are some causes of structural deterioration?

- Compaction by farm equipment
- Deforestation
- Forest fires
- Over grazing/cultivation

What are seven strategies used in agriculture to manage soil?

- Terracing and contour ploughing
- Crop rotation and cover crops
- Strip cropping
- Afforestation with shelter belts
- Controlled grazing
- Improved drainage
- Management of irrigation