Chapter 8 - Soil

• What is the main control on the soil type?

  Controlled largely by the parent rock. It controls the colour, nutrients quality, ph of the soil and drainage properties.
• The 4 things that make up soil

  • air
  • rocks/minerals
  • organic matter
  • water
• The inputs of soil

  • gases from atmosphere
  • precipitation
  • nutrients from parent rock
  • organic matter from decay of organisms
• Outputs of soil

  • soil erosion
  • evapourtranspiration
  • leaching of the soil
• What system are soils?

  Soils are an open system.
• Stage 1: Weathering

  • Weathering breaks apart the parent rock into pieces and forms the regolith
  • Clay particles join together (process of aggregation)
• Stage 2 : Colonisation/humification

  • Once the rock has been broken apart, organisms such as algae/ lichens can start to colonise the area, and then add organic matter to the soil when they die.
• Role of earthworms in the soil

  • break organic matter into smaller pieces
  • mix and aerate the soil
  • increase the soul pH
  • improve the soil stucture
• What is the humification?

  Process by which dead organic matter is decomposed to form humus.
• Chelation

  As the organic matter decomposes, it releases nutrients and organic acids, these acids attack clays releasing iron and aluminium
• Stage 3 : Translocation

  • Movement of soil components in any form or in any direction
  • Occurs with greatest effect with either very high or very low rainfall.
  • Most common in tropical or desert climates
• Leaching

  Common in areas of intense high rainfall.

  It is the carrying of elements in a dissolved form.
• What is leaching controlled by?

  Solubility of an element

  The more soluble a mineral is the greater is suspectibilty to leaching

  Rainfall

  Leaching becomes more rapid as the percolating water becomes more acidic.
• Parent rock material( factors affect formation of soil)

  Controls

  • soil colour, therefore temperature
  • mineral component
  • soil texture, which affects the drainage of the soil
  • soil depth
• Climate( factors affect formation of soil)

  Climate affects the rate of weathering.

  In hot arid climates, high temperatures draw moisture up to the surface.

  This is called salinisation.
• Topography( factors affect formation of soil)

  • Precipitation increases with altitude but temperatures decrease.
  • Valley floors have deeper soil due to soil creep downwards
  • A steep slope means, increased drainage, increased soil erosion, increases run off
• Soil biota( factors affect formation of soil)

  Plants:

  Add organic matter when they die. Humic acid are released during decomposition and may break down the clays.

  Worms:

  mix and aerate the soil.

  Fungi/bacteria

  assist in decomposition and decay of dead vegetation which releases humic acids to the soil. The bacteria can also fix nitrogen and assist in nitrification of the soil.
• Time( factors that affect formation of soil)

  The longer the soil has to form, the greater the weathering and organic matter breakdown; meaning deeper soils to support a higher species diversity
• Soil organic matter practical (Step 1)

  • Use the dry sample of soil, place the crucible with soil onto the tripod and clay pipe triangle above the bunsen burner
• Soil organic matter practical (Step 2)

  • Light bunsen burner and heat the sample, maintain a red glow on the crucible for 30 minutes
• Soil organic matter practical (Step 3)

  • Allow to cool
• Soil organic matter practical (Step 4)

  Measure the mass of the crucible with the burned soil
• Soil organic matter practical (Step 5)

  Use the equation below to calculate soil organic content as a % of dry mass

  Soil organic content as % of dry mass= ( C - D ) / ( C -A ) X 100
• Soil compaction practical (Step 1)

  • Hold the knitting needle perpendicular to the ground at a height of 1 metre and let go
• Soil compaction practical (Step 2 )

  • Hold the knitting needle at the surface of the soil
• Soil compaction practical (Step 3)

  • Pull out from the soil and measure the length of knitting needle ( mm ) that was in the soil