Soil Problems and Management

• What is salinisation?


  the build up of salts in the soil eventually to toxic levels for plants
• The world has already lost 1/3 of fertile soils
• Soil Erosion


  The wearing away of the top layer of soil (the topsoil)
• Leeching


  A process by which heavy rainfall infiltrates through soil, removing humus and nutrients in solution
• The topsoil is the most fertile layer of soil because it contains the most organic, nutrient-rich materials. This is the layer that farmers want/need to protect for growing their crops and for animals to graze on.
• It takes 200 to 1,000 years for one inch of nutritious soil to form, emphasising the importance of preserving existing soil resources.
• 24 billion tons of fertile soil is lost each year
• What are the different causes of soil erosion?

  1. Wind erosion
  2. Water erosion
  3. Waterlogging
  4. Salinisation
  5. Structural deterioration of soil
• Waterlogging:

  Soil is considered to be waterlogged when too many of the pore spaces in the soil are occupied by water rather than air. Leading to an insufficient amount of oxygen (anerobic conditions) for plants to respire.
• Structural deterioration of soil


  The breakdown of the natural arrangement of soil particles into aggregates or peds. These new groupings often form distinctive shapes and are typically found within certain soil horizons.
• Wind erosion is the process by which soil particles are detached, lifted, and transported by the force of wind. It typically occurs in dry, arid, or semi-arid regions with loose, sandy soil and minimal vegetation cover.
• Water erosion is the process by which soil is worn away and transported by the action of water. This occurs when rain, surface runoff, or flowing water removes the topsoil, which is the most fertile layer of the soil.
• Name the ways of controlling water erosion:

  The key to doing so is to reduce the amount of surface flow of water. This is done by:

  • Installing and maintaining field drains and ditches. Sediment should be removed from ditches and replaced in the fields where it came from.
  • Reducing the amount of water running off roads and farm tracks onto fields
  • Using manure to stabilise the topsoil
  • Protecting soil in winter by early sowing or the use of cover crops
  • Contour ploughing—this reduces overland flow and the formation of rills and gullies.
• Rills and gullies are both channels in soil caused by erosion from flowing water, but they differ in size and how they form:

  • Rills: Shallow channels, usually less than a few inches deep, that form in soft, bare soil. Rills are often the first sign of erosion and can be repaired by tilling. They are most likely to form in areas with lots of rainfall or on soft soil.
  • Gullies: Large, wide, and deep channels that form when rills become too big to repair. Gullies are difficult to repair and can be impacted by human actions like cutting down trees, leaving land bare, or driving on soft soil. 

  
• Name the different ways wind erosion is controlled:

  1. Organic matter (e.g. manure) to the soil helps to improve the soils structure
  2. Increasing the roughness of the soil's surface or by leaving crop residues or stubble in fields and not ploughing them into the soil.
  3. Increasing plant cover to about 50% reduce the surface wind speed, giving protection
  4. Planting lines of trees of hedgerows cuts wind speed, which reduces both evaporation (by up to 20%) and wind erosion. A tree line has wind speed reduction effect for up to 12 times the height of that tree both before and after the barrier

  
• Waterlogging:

  • Occurs when soil is oversaturated.
  • A lack of oxygen in the root zone of plants causes their root tissues to decompose. This leads to the plants growth and development being stalled. If the anaerobic circumstances continue for a considerable time, the plant eventually dies. Waterlogging usually does not last long enough to kill the plants but can cause a low yield for farmers.
• Waterlogging occurs under two conditions:

  1. Surface-fed waterlogging happens when precipitation, irrigation water or river floodwater exceeds the combination of evapotranspiration and percolation so that the water stays in and on the surface of the soil
  2. Groundwater-fed waterlogging is caused when the rate of rising groundwater is not matched by the rate of evatranspiration. This may be a natural rise in groundwater or be caused by irrigation canals.
• Ways to control/manage waterlogging include:

  1. Adding field drains to help reduce water logging as they ensure air is able to get into the soil
  2. Land Grading (modifying landscape)
  3. Adding compost to improve soil structures ability to absorb water.

  
• Salinisation effects 10-20% of farmland globally. Particularly effecting semi-arid areas that are poorly drained and use a lot of irrigation water. E.g., China’s Northern Plain
• Causes of Salinisation:

  • When irrigated water is evaporated, they leave salt behind
  • Irrigated water refers to water that is artificially supplied to crops, pastures, or plants to support their growth, especially in areas where natural rainfall is insufficient or unreliable.Common Sources of Irrigated Water:

  1. Surface Water: rivers, lakes, reservoirs, or canals.
  2. Groundwater: Pumped from wells or aquifers.
  3. Recycled Water: treated wastewater or runoff.
  4. Rainwater Harvesting: Stored water collected from precipitation.
• Ways to control/manage salinisation include:

  • Flushing the soil with lots of water. Though this results in the salinisation of rivers and groundwater where the flushed water goes
  • In extreme cases, when the salt crust is too thick, it cannot be flushed as the water runs off the salty surface; in this case, the area is abandoned.
• Soil Structures can be classified as follows:

  1. Granular and crumb structures
  2. Blocky structures
  3. Prismatic and columnar structures
  4. Platy Structures
• Causes of Structural deterioration of soil

  1. Reduction in Soil Organic Matter:

  • Cultivation disrupts soil
  • Less organic material is returned to the soil because crops are harvested, removing plant matter.
  • Low organic matter weakens soil, making it prone to breaking apart under stress. This can form a hard surface crust, preventing water movement and seed growth.

  1. Soil Compaction:

  • Heavy pressure (from vehicles, ploughing, and livestock) compresses soil, reducing its ability to absorb water.
  • Repeated pressure creates impermeable layers (e.g., plough pans).
• Solutions for Structural deterioration of soil

  1. Reducing Soil Disturbance

  • Minimise ploughing and adopt no-till or reduced-till farming to preserve soil structure.
  • Direct Seeding: Plant seeds without extensive soil disturbance to avoid physical fracturing.

  1. Preventing Soil Compaction

  • Controlled Traffic Farming: Limit vehicle movement to specific paths to reduce overall soil pressure.
  • Reduce Heavy Machinery Use: Avoid driving heavy vehicles on wet soils, which are more prone to compaction.
• What are the different types of water erosion in soils:

  A) Rill

  B) Gully

  C) Sheet

  D) River Bank

  
• The different types of wind erosion include:

  A) Saltation

  B) Abrasion & Attrition

  C) Creep

  D) Suspension