Soil
Primary 4 · Science and Elementary Technology
Soil
Lesson 1 of 5
15 min
Let's begin
Ishimwe helps his grandfather dig the garden. Near the river the soil is pale and gritty and runs through his fingers. Down in the valley it is grey and sticky. On the hillside garden it is dark and crumbly. "Is it all the same soil?" he asks.
No. There are different types of soil, and each one behaves differently.
Soil is the loose top layer of the ground, where most plants grow. It is a mixture of tiny pieces of rock, dead plant and animal matter, water and air, with many small living things.
Soil forms very slowly. Sun, rain, wind and plant roots break rocks into smaller and smaller pieces, and dead leaves and animals rot and mix in. It can take hundreds of years to make just a few centimetres of soil. That is why soil is so precious.
| Sandy soil | Clay soil | Loam soil | |
|---|---|---|---|
| Particles | Big, gritty grains | Very tiny grains | A mix of sand, silt and a little clay, with humus |
| Feel | Rough; falls apart | Smooth and sticky when wet; hard and cracked when dry | Soft and crumbly |
| Water | Drains away very fast; dries quickly | Holds a lot of water; drains very slowly | Holds enough water and lets the rest drain |
| Air | Plenty | Very little | Enough |
| Good for | Building (mixing concrete) | Pots, bricks and tiles | Growing crops: the best farming soil |
Silt has grains in between sand and clay. It feels smooth like flour and is often left behind by rivers.
Tip
Sand is gritty, clay is sticky, loam is just right
Like the three bowls of porridge: sand is too dry, clay is too wet, and loam is just right for crops.
Try each one first, then tap Show answer to check.
What is soil?
Answer: The loose top layer of the ground: a mixture of tiny rock pieces, dead plant and animal matter, water, air and living things.
Mutesi's soil is sticky and rolls into a thin snake. Which type is it?
Answer: Clay soil.
In the drainage test, which soil lets water through fastest?
Answer: Sandy soil, because its big grains have big spaces between them.
Which soil is best for growing beans and maize, and why?
Answer: Loam, because it holds enough water and air and is rich in humus.
What you learned today
Sources and credits
The exercises (Try it yourself and the practice questions) are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
Quick check
Match each soil to how it feels.
Tap one on the left, then its partner on the right.
