Types of Soil - Class 4 Notes & Olympiad Questions

Layers of Soil

1. Topsoil

a) The topsoil is the uppermost layer of soil, and it is very important for plants because it is rich in minerals and humus.
b) Humus helps make the soil fertile, and the topsoil is also soft and can hold water well. That's why most plants are grown in this layer.
c) Many different organisms like earthworms, rats, snakes, beetles, and more live in the topsoil, making it their home. It has a dark colour.

2. Subsoil

a) Below the topsoil, we have the subsoil, which is harder and contains fewer nutrients and less humus. It is grey in colour.
b) Subsoil holds water for plants to use.

3. Weathered Rock Fragments

a) Further down, we find a layer called weathered rock fragments. In this layer, there is very little or no plant life because it is not suitable for plants to grow.

4. Bedrock

a) Finally, beneath the subsoil, we have the bedrock. It is a hard layer that cannot be dug manually.
b) The upper side of the bedrock is porous, meaning it has tiny holes, while the inner side is non-porous, which means it doesn't have holes.
c) Bedrock acts as a foundation for the layers of soil above it.

Types of Soil

1. Sandy Soil

a) Sandy soil is made up of small, fine grains that create spaces or pores in the soil. This makes it porous, allowing water to easily pass through. However, sandy soil doesn't hold water very well.
b) It can be carried by the wind and is often found in areas where windblown soil is common.
c) Plants adapted to grow in soil with low water-holding capacity and good drainage thrive in sandy soil.

2. Clayey Soil

a) Clayey soil is composed of very fine particles that stick together.
b) The particles in clayey soil are closely packed, which means there is less air in the soil. However, clayey soil has excellent water-holding capacity, which means it can retain water for plant growth.
c) Clayey soil is also used in making various things like toys, pots, and other articles.

3. Loamy Soil

a) Loamy soil is a mixture of sand, clayey soil, and humus, which is organic matter.
b) It has a balance of different particle sizes, making it ideal for plant growth.
c) Loamy soil can hold water well, allowing plants to access it, and it also has good aeration, providing air to the plant roots.
d) It contains a significant amount of humus, which is beneficial for plant nutrition.
e) Overall, loamy soil is considered suitable for plant growth compared to sandy or clayey soil.

Soil Erosion

a) Soil erosion is when the valuable top layer of soil, which is good for growing plants, gets washed away or blown away. This makes the soil less fertile and not as good for plants.
b) The top layer of soil is light, so wind and water can easily carry it away. When wind and water remove this topsoil, it's called soil erosion.

Biodegradable and Non-biodegradable Substances