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Getting The Dirt On Soil

A flow chart showing classifications of soil according to touch and pliability

Get your hands dirty and come to grips with soil

Australian Curriculum Links

  • Science > Earth and space sciences > Year 4 > ACSSU075

You’ll Need

  • Clean glass jars with lids (one per individual)
  • Whiteboard markers
  • Trowels
  • Spray bottle for water
  • Soils collected around the area

Try this

  1. As a group, collect soil from around the area, including parks, gardens and school yards.
  2. Record where each sample was collected from. Each sample should be enough to fill a glass jar.
  3. Study the samples. What colour are they? What can you see in the soil: stones, sticks, sand?

Part A

  1. Take a small amount of soil and place it in the palm of your hand.
  2. Spray it lightly with water and try to roll it into a ball.
  3. Is the soil gritty? Is it sticky? Is it silky? Will it roll into a ball easily? Is it hard to squeeze? Use the key (pictured above) to classify your soil.

Part B

  1. Take your clean glass jar and fill it with soil to one-third of its height. Mark that height on the side of the jar with a whiteboard marker.
  2. Cover with twice this height of water and mark this level with a marker.
  3. Observe what happens when you add water. Were there many bubbles? Did some parts of your sample float to the top?
  4. Stir or shake (if you have a firm-fitting lid) thoroughly and allow the sample to settle for a few hours.
  5. What do you see now? Has your sample settled out into different layers? Have the heights of the water and soil changed? Are there different colours in the layers? Are there different sizes of soil particles in your soil?

Further investigation

  • Did you notice if your samples were similar or different?
  • Did samples from similar areas have similar characteristics?
  • Create a map of where samples were collected to see if you can group similar soils by location.

What’s Happening?

Soil is made up of different sized particles of minerals that are from broken down rocks. The largest particles are sand, which allows water to drain freely but does not retain nutrients for plants. The smallest particles are clay particles. Clay soils retain water and nutrients. This can cause problems because they can become waterlogged and muddy. Silt particles are slightly larger than clay particles and can still hold some nutrients. Loam is a mixture of sand, silt and clay. It can allows water to drain without drying out and is able to hold nutrients. You can feel gritty sand particles and the stickiness of clay.

When we cover the soil with water, stir and allow it to settle, the soil will break down into its different particle sizes. Did you notice any bubbles or that the water level dropped as the soil settled? This is because soil contains a lot of air. These pores of air allow rain water to be absorbed. Bigger soil particle sizes lead to bigger pores for water to flow through quickly.

Did you notice any sticks or twigs in your soil? Healthy soil contains organic matter such as twigs and pieces of plant roots. This organic matter absorbs water and slows the flow of nutrients.

Further information

Healthy soil not only contains minerals and old roots, it also contains fungi, which help breakdown plant matter. Fungi capture nutrients and water from the soil using fine threads called mycelium, which is shared with plants. These mycelium stretch out and form large colonies of fungus. The largest is a colony of fungus in America, which is over 8 km2. It is about 2,400 years old and one of the largest living organisms in the world.