The earth beneath our feet

Yasmin Jayathirtha

After looking at experiments that we can do with ‘earth in a bottle’ it is time to come down to earth and consider what we can learn about the soil in our neighbourhood. We have learnt that environmental factors decide the type of soil present in a place and deforestation and runoff can degrade the quality of soil and this has an effect on the vegetation that can grow there. A lot can be learnt by observation, but some very simple experiments can illustrate the ideas effectively.

Soil is that part of the earth where life flourishes and is divided into top and sub soil. Soil is made up of six main components: rock particles, soil water, organic matter (humus), air, lime and mineral salts. It is the combination of these that makes up the quality of the soil. We can look at each of these factors in turn.

soil-particles Equipment:

  • Gas jars with lids
  • Test tubes
  • Beakers
  • Crucibles – steel katoris can be used
  • Funnels and filter paper
  • Measuring cylinders
  • Tin cans
  • Concentrated hydrochloric acid
  • pH papers/universal indicator solution
  • Access to a balance
  • Access to an oven
  • Desiccator – a simple one can be made by taking a stainless steel box with a tight fitting lid. Use silica gel desiccant as the drying agent

Soil particles: The size of the particles vary from place to place. Very degraded slopes will have large particles, while tank and pond bottoms will have very fine silt that has been washed down.

Collect samples of soil from various places. Get a sample of sand for comparison.

Half fill a gas jar or test tube with the soil sample. Add water till it is about three-quarters or more full. Notice the air bubbling out. Cover and shake. Let it stand. The soil settles down with the heaviest particles at the bottom and humus floating on top. It is a very graphic illustration of soil types.

The author works with Centre for Learning, Bengaluru. She can be reached at yasmin.cfl@gmail.com.

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