Soil Ladder

Age Group: 9-12 years

Duration: 20 minutes

Biomimicry Connection:

Connected to the leaves we can easily observe how nature recycles all materials.

Activity Details:

Tools and Materials

• Small spades for each group
• Simple identification key for animals living in soil

Preparation

Find an area with trees and decaying leaves, where pupils can dig soil 'pits'. Before carrying out the activity, ensure you are in a place where no rare or protected species can be found. After completing the activity, ensure all soil and vegetation is replaced as you found it.

Description

Nature does not mine the Earth’s crust for materials to make things. It makes use of everything around us, including decaying organisms, as the raw materials for new life. In this activity pupils investigate the process of decomposition from vegetation to soil. This activity works well in a woodland where the decomposition of leaves into soil is usually very clear.

1. Divide the pupils into groups of 4–5. Ask each group create a ‘ladder’ on the ground from sticks (see image below), with each square 40–50 cm wide.
2. After marking the squares, follow the instructions below.
   • Square 1 - leave untouched.
   • Square 2 - remove whole, not decaying, leaves, needles, sticks, herbaceous plants.
   • Square 3 - see 2 and also remove decaying leaves needles, which can be still identified.
   • Square 4 - see 3 and also remove humus (dark layer with organic materials in it) down to mineral soil level (no organic ingredients).
3. Ask each group to observe the steps of humus formation i.e. square 1 to 4. Investigate the animals living in the different levels (it is good if you have a simple identification key) and the different size of soil particles.

Extension

A soil profile can be dug vertically into the soil, demonstrating the same results. Using a small spade, pupils take samples from each square at different depths as follows:

1. Collect a sample of vegetation from the surface.
2. Take a sample of soil/decaying vegetation from 5 cm depth.
3. Take a sample of soil from 10 cm depth.
4. Take a sample of soil from 15 cm depth.

Additional Information

Recycling is a great thing we can learn from leaves and the rest of nature. A key natural cycle is the food web and parts of it are the decomposers. Leaves in temperate zones grow each spring and fall down in the autumn. What happens to them?

We can see that they become yellow or red or brown at first, and then they fall down. These colours mean that some of their components have broken down and were transported to the roots or to other organs for storing.

The remainder of the leave falls to the ground. In the autumn we often walk through a deep carpet of leaves. Tiny decomposers (insects, bacteria, fungi) live in the soil and work hard breaking down these leaves into leaf mould. Every component will enrich the soil and be available for the next generation of trees.

And what about the evergreens? Do their leaves live forever?

No, the leaves of evergreens fall down as well, just not at the same time. They change leaves continuously and the decomposition works for them as well.

We can learn from the decomposing of leaves how in natural systems everything is recycled. We can learn about recycling from the way leaves are part of the nutrient cycle. Nothing gets wasted and everything is used again. Currently, even the best human recycling systems still create waste which can cause pollution.