Soil

What is soil?

Soil is a thin layer of material on the Earth’s surface

It’s a very important natural resource

Soil composition

Soil composition

  1. [[Mineral Matter[[
  2. ]]Air]]
  3. {{Water{{
  4. }}Humus}}
  5. <<Living organisms<<

[[1. Mineral Matter[[

  • Main ingredient in soil
  • Weathered and eroded rock particles
    • Stones
    • Sand
    • Silt
    • Clay
  • Provides minerals to help plants grow

]]2. Air]]

  • Fills spaces between rock particles
  • Air contains oxygen and nitrogen
    • plants need this to survive
  • Needed by living organisms

{{3. Water{{

  • Helps to bind soil
  • Dissolves minerals so plants can absorb them

}}4. Humus}}

  • Forms when animals and plants decay and rot
  • Jelly like substance
  • Provides nutrients
  • Makes soil fertile

<<5. Living Organisms<<

  • Earthworms
  • Bacteria
  • Fungi
  • Insects
  • Burrowing animals
  • Mix up the soil
    • Allow air and water to pass through the soil
  • Break down plants and animals => organic material

Soil texture

  • What the soil feels like
  • Three groups:
    • sand
    • silt
    • clay
  • Particles of sand => largest
  • Particles of clay => smallest

Soil profiles

O Horizon

This layer contains organic material. Lots of plant litter (leaves and rotting vegetation) which provides humus for the soil

A Horizon

Upper layer of soil also known as top soil. Where most of the living organisms live. It’s darker as it has the highest humus content, meaning it’s also the most fertile

B Horizon

Also know as subsoil. Lighter in colour as it contains less humus however there is more stones as it is located closer to the bedrock

C Horizon

This layer is called bedrock or parent material. The lower section is solid rock but the top section may be broken into rock particles

Leaching

  1. Water passes through the soil when it rains
  2. This washes minerals, humus and nutrients from the A horizon to the B horizon

Most plant roots are located in the A horizon, plants can’t access the minerals, humus and nutrient that are in B horizon which can affect their growth

In extremely wet conditions minerals build up between the two horizons. It becomes cemented together to create an impermeable layer. Water can’t flow through making the soil above water logged

Brown Earth soils

  • Most common soil type in Ireland
  • Lowland areas
  • Formed on boulder clay that was glacially deposited
  • Loam => even mix of sand, silt and clay
  • Ideal for crops
  • Deciduous forests
  • Lots of humus => fertile
  • Very little leaching

Influence of soil on vegetation

Depth

  • Deep fertile soils => support a wide variety of crops => high nutrient content
  • Shallow infertile soils => limited type of vegetation

Acidity

  • Some plants such as rhododendrons grow in acidic soil
  • Not many plants grow in acidic soil
  • Lime => spread on land => reduce acidity => increase fertility

Drainage

  • Clay soil => easily waterlogged => difficult to cultivate
  • Sand soils => well drained => support a wide range of crops

Influence of vegetation on soil

Plant litter

  • Vegetation => plant litter => humus => fertile soils
  • Soil under deciduous trees are more fertile because there is more plant litter

Soil erosion

  • Bind and protects soil from mass movement
  • When the vegetation is lost it becomes vulnerable to erosion

Leaching

  • Vegetation acts as an umbrella against rain
  • Less water gets into the soil => less leaching

Human interference with soil

1. Deforestation

Cutting down of trees for economic purposes

Two major effects:

  1. Removal of trees reduces plant litter => soil loses fertility
  2. Exposure of soil can lead erosion, flooding and mass movement
    • Flooding: low land areas
    • Mass movement: Up land areas

==Solution==: Forest management and reforestation (plant of trees)

2. Intensive farming

Lead to desertification => expanding of desert

==Example==: The Sahel

  1. Over-cropping
    • Crop continuously grown on land => nutrients removed => soil becomes exhausted
      • Mainly by mono culture (1 type of crop) and cash crops
      • Example: coffee or cotton
    • ==Solution==: Careful management and crop-rotation
  2. Overgrazing
    • Too many livestock on a piece of land => intensive grazing => vegetation and roots destroyed
    • Soil is left open and vulnerable to erosion and weathering
    • ==Solution==: changing farming practices and education