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Soil and what grows in it

Learn how soil forms from rock, what its layers are, the three main types of soil and which crops grow best in each.

Get the whole book: Science for classes 3 to 5 (9 lessons, free to print)

Let us begin

The big idea

Soil is the loose brown layer on the ground that plants grow in. It took thousands of years to form from rocks. In this lesson you will dig into what soil is made of and why farmers care so much about it.

Soil forms when big rocks break into smaller and smaller pieces because of sun, rain, wind, ice and the roots of plants. This slow breaking is called weathering. Dead leaves, plants and animals rot and mix in, making a dark material called humus. Humus makes soil rich and holds water.

If you dig a deep pit you see layers. The top layer is topsoil: dark, soft and full of humus, roots, worms and insects. Below it is subsoil, which is lighter in colour with more sand, clay and small stones. Under that are broken rocks, and at the bottom is solid bedrock.

Soil is sorted into three main types by the size of its particles. Sandy soil has large particles, feels gritty, and water drains through it quickly. Clayey soil has very tiny particles, feels sticky when wet, and holds water for a long time. Loamy soil is a mix of sand, clay and humus; it holds just enough water and is the best for most crops.

Different crops like different soils. Rice needs standing water, so it grows well in clayey soil. Wheat, pulses and most vegetables grow best in loamy soil. Earthworms and insects dig tunnels in soil, letting air and water reach plant roots, so they are a farmer's friends.

Soil can be washed away by heavy rain or blown away by wind when there are no plants to hold it. This is called soil erosion. Trees and grass hold the soil with their roots, so planting them protects the soil.

Layers of soilA tall cross-section of the ground. A plant with roots grows on the surface. Below it four stacked layers are labelled: topsoil with humus and roots, subsoil with sand and clay, broken rock, and bedrock at the bottom. Topsoil dark, humus, roots, worms Subsoil lighter, sand, clay, stones Broken rock Bedrock solid rock, no plants roots Soil takes thousands of years to form from rock.
Dig down and you find these layers: topsoil, subsoil, broken rock and bedrock.

Worked examples

See how it works

  1. The jar test

    Put a handful of garden soil in a glass jar, fill it with water, close the lid and shake. Let it stand for an hour. The heavy sand settles at the bottom, the finer silt settles above it, the tiny clay stays near the top, and bits of humus float. The layers show what your soil is made of.

  2. Which pot dries first?

    Fill one pot with sand and another with clayey soil and water both equally. The sandy pot dries first because water drains straight through the big gaps between sand grains. The clayey pot stays wet because its tiny particles hold the water.

  3. Choosing a soil for rice

    A farmer wants to grow rice. Rice plants need their roots in standing water for weeks. Sandy soil would let the water run away, so the farmer chooses clayey soil, which keeps the field flooded.

Try it at home

Soil in a bottle

You will need

  • A clear plastic bottle or glass jar with a lid
  • Water
  • Two handfuls of soil from a garden or pot
  • Paper and a pencil

What to do

  1. Put the soil in the bottle until it is about one third full.
  2. Add water until the bottle is almost full, close the lid and shake well for a minute.
  3. Stand the bottle still and watch. Note what settles first and what floats.
  4. After an hour, draw the layers you see and label them: sand, silt, clay, humus.
  5. Wash your hands well when you finish.

Ask a grown-up: Ask an adult before collecting soil from outside, and wash your hands with soap afterwards.

Practice sheet

Check what you learned

Write your answers in a notebook, or print this sheet and write on it. When you finish, mark your work with the answer key.

Practice sheet: Soil and what grows in it (Classes 3-5, Science)

  1. What is the slow breaking of rocks into soil called?
  2. What is humus?
  3. Which soil layer is dark and full of roots and worms?
  4. What is found at the very bottom, under all the soil layers?
  5. Which type of soil has the largest particles?
  6. Which soil feels sticky when wet and holds water a long time?
  7. Which soil is a mix of sand, clay and humus and is best for most crops?
  8. Why is rice grown in clayey soil?
  9. How do earthworms help plants?
  10. What is soil erosion, and how do trees stop it?

Answer key

Answers: Soil and what grows in it

Do the practice sheet first, then check here. If an answer is different from yours, read the lesson again and try once more.

  1. Weathering.
  2. Rotted remains of dead plants and animals mixed into the soil; it makes soil rich.
  3. Topsoil.
  4. Bedrock (solid rock).
  5. Sandy soil.
  6. Clayey soil.
  7. Loamy soil.
  8. Clayey soil holds standing water, which rice plants need.
  9. They dig tunnels so that air and water can reach the roots.
  10. Soil being washed away by rain or blown away by wind; tree roots hold the soil in place.

What next

Keep learning

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Science for classes 3 to 5

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