Science Experiment – Soil

By AG Education 12 December 2017
Reading Time: 2 Minutes Print this page
Discover the power of soil as a water filter

About this experiment

Healthy soil is important for strong plant growth. Events like rainstorms can cause runoff that washes away many of the nutrients in the soil. Some soil environments are more likely to experience erosion than others. In this experiment, you can create different soil environments and test how the presence of greater biomatter impacts the degree of erosion. How do different soil environments act as water filters?


  • 6 empty plastic 2L bottles
  • Cutting blade and scissors*
  • Permanent marker
  • Soil from garden
  • Soil from compost
  • Handful of mulch (bark chips, sticks, dead leaves)
  • Handful of gravel
  • A few small seedlings
  • Water
  • Table

*Safety warning: make sure you have a parent or teacher to assist.


  1. Take three of the bottles, mark a rectangle roughly 25cm x 7cm down the side of each, and use the blade to cut a hole. Place the bottles on a table with the holed sides face-up and the bottle necks sticking out a little over the edge.
  2. Fill the first bottle with plain garden soil, pressing down firmly to make sure the bottle is full and the soil is compact. Do the same with the next bottle, adding a mixture of mulch and gravel to the surface. Fill the last bottle with compost soil and firmly plant the seedlings close together. These bottles are now your “terrariums.”
  3. Next, cut the remaining four bottles in half, horizontally. Keep the bottom halves, which have become “buckets” (you can recycle the top halves.) Near the rim of each bucket, puncture a pair of small holes on opposite sides.
  4. Cut four pieces of string, about 25cm in length, and run them through the holes, knotting the ends, so you can hang each bucket over the neck of a terrarium.
  5. Now, pour equal amounts of clean water into the ends of each terrarium. Watch as the water slowly trickles down into the buckets.
    How do the water colours differ? Have any materials collected in the water
  6. Compare the results from each soil environment.
    Which natural elements seem to better strengthen the soil and control run-off and erosion?

The more biomatter there is in the soil, like nutrients, root structures from plants, or mulch, the more stable the soil is, minimising erosion and keeping water clean. This is one example of why healthy plants and organic materials are so important for our gardens and our environment!

Do you want to keep learning? Find more experiments here!