Soil Science – JSS1 Intermediate Science Lesson Note (Second Term)

WHAT IS SOIL?

If you look at a farm, a garden, or even the football field, you are looking at Soil. Soil is the top layer of the earth’s surface where plants grow. It is not just “dirt”—it is a living system made of tiny rocks, water, air, and decayed plants and animals (which we call humus).

How is Soil Formed?

Soil doesn’t just appear. it is made through a very slow process called Weathering. This is when big rocks are broken down into tiny grains by:

• Rain: Water washing over rocks.
• Wind: Blowing against the rocks.
• Plants: Roots growing into cracks and breaking rocks apart.
• Heat: The sun making rocks expand and crack.

Fun Fact: It can take hundreds of years just to make one centimeter of soil!

TYPES OF SOIL

Not all soils are the same. If you go to the beach, the soil feels different from the soil in a yam farm. There are three main types of soil:

1. Sandy Soil

• Feel: It feels gritty and rough when you rub it between your fingers.
• Particles: The grains are large and have big spaces between them.
• Water: Water runs through it very fast. It does not hold water well.
• Where to find it: At the beach or in deserts.

2. Clayey Soil

• Feel: It feels smooth and sticky when wet. When dry, it becomes very hard.
• Particles: The grains are very tiny and packed tightly together.
• Water: It holds a lot of water and can become waterlogged (soaked) easily.
• Where to find it: In swampy areas or riverbanks.

3. Loamy Soil

• Feel: It feels moist and crumbly.
• Composition: It is a perfect mixture of sand, clay, and plenty of humus (dark, decayed plant matter).
• Water: It holds just the right amount of water—not too much, not too little.
• Best for: This is the “King of Soils” for farmers!

PROPERTIES OF SOIL

To understand soil better, we look at its properties. These tell us how the soil will behave when we plant in it.

1. Texture

This is how the soil feels (rough, smooth, or crumbly). Texture depends on the size of the soil particles.

2. Water-Holding Capacity

This is the ability of the soil to keep water.

• Clay has high water-holding capacity.
• Sand has low water-holding capacity.

3. Porosity (Air Spaces)

This is how much air space is between the soil grains. Plants need air in the soil to breathe through their roots. Sandy soil has the most air space, while clay has the least.

4. Color

• Dark brown or black soil usually means it is rich in food (nutrients) for plants.
• Red or yellow soil often means it has a lot of iron.
• Light-colored soil usually has more sand.

IMPORTANCE OF SOIL TO PLANTS & AGRICULTURE

Without soil, we would have no food to eat! Here is why soil is so important:

1. Anchor for Plants: Soil holds the roots of plants firmly so they don’t fall over when the wind blows.
2. A Store of Water: Soil acts like a sponge, holding water that plants drink to stay alive.
3. A “Kitchen” for Nutrients: Soil contains minerals (like Nitrogen and Potassium) that plants use as “food” to grow big and produce fruits.
4. Home for Living Things: Soil is full of life! Earthworms, ants, and tiny bacteria live in the soil. They help break down dead leaves to make the soil richer.
5. Human Needs: We use soil to build houses (bricks are made of clay), make pots, and even for road construction.

Class Activity

Let’s be Soil Scientists!

1. Get three cups. Fill one with sand, one with clay, and one with loam.
2. Pour a little water into each.
3. Observe: Which one swallowed the water immediately? Which one kept the water sitting on top?
4. Touch: Which one can you use to mould a small ball?

Revision Questions

1. What is the name of the dark, organic part of the soil made from dead plants?
2. Which type of soil is best for planting maize? Why?
3. Why is Sandy soil not good for most crops?
4. Mention two things that help break rocks into soil.

Homework

Find a small sample of soil near your house. Write down its color, how it feels, and whether you think it is Sand, Clay, or Loam.