What Soil Is Made Of

1The parts of soil

Good soil is made of five things:

1. Mineral particles: tiny pieces of broken rock, such as sand, silt and clay. They make up nearly half of the soil.
2. Humus: dark matter made from dead leaves, roots and animals that have rotted. Humus is full of plant food (nutrients) and soaks up water like a sponge.
3. Water, held in the tiny spaces between the particles.
4. Air, also in the spaces between the particles. Roots and soil animals need it to breathe.
5. Living things: earthworms, termites, ants, beetles, and tiny bacteria and fungi. They break dead matter down into humus, and earthworms dig tunnels that let air and water in.

In a good soil, about half is solid (mineral particles and a little humus) and about half is spaces, filled with water and air.

2Experiments to find the parts of soil

• Air in soil: drop a lump of dry soil into water. The bubbles are air escaping from the spaces.
• Water in soil: put some fresh soil in a clean jar, close the lid and leave it in the sun. Drops of water form on the inside of the glass.
• Particles and humus (jar test): half fill a jar with soil, add water, close it and shake hard. Leave it for a day. Stones and sand settle at the bottom, then silt, then clay on top. Bits of humus float on the water.
• Living things: spread a handful of garden soil on a paper and look closely, with a hand lens if you have one. Count the tiny animals, then put them back gently.

Try it yourself

Try each one first, then tap Show answer to check.