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Lesson Explainer: Types of Soil Science

In this explainer, we will learn how to describe the composition of different types of soil and identify plants that can grow in each.

Have you ever noticed that not all soil is the same?

Different types of soil

Though most soil is brown, different soils from different places look and feel different.

In this explainer, we will consider some of the differences between different types of soil and why they are important.

First, let’s recap what we already know about soil.

We already know that soil is a mixture of

  • rock particles,
  • organic matter,
  • minerals,
  • air,
  • and water.

We have learned that the organic matter of soil consists of decomposed plants and animals. We call this humus.

Humus provides nutrients that, alongside minerals, help plants to grow healthily.

Different soils look and feel different. This is because they are made up of different components.

The three types of soil we will learn about in this lesson are silt, sand, and clay.

Example 1: Identifying Types of Soil

Which of these is not a type of soil?

  1. Silt
  2. Humus
  3. Sand
  4. Clay

Answer

Silt, sand, and clay are all types of soil, so options A, C, and D are incorrect.

Humus is not a type of soil. Humus is a component of soil.

Humus is the organic matter of soil, consisting of decomposed plants and animals.

Silt, sand, and clay soils all contain humus.

So, the correct answer is option B: humus is not a type of soil.

Clay, silt, and sand soils are composed of different particles.

Note that clay soil does not contain only clay particles, silt soil does not contain only silt particles, and sand soil does not contain only sand particles.

All three soil types are mixtures.

They each contain some clay, silt, and sand particles in different amounts.

Definition: Clay Soil

Clay soil is a soil type composed mainly of clay particles, silt particles, a small amount of sand particles, and humus.

Definition: Silt Soil

Silt soil is a soil type composed of a mixture of gravel (small stones), sand, clay, silt, and larger amounts of humus than clay or sand soils.

Definition: Sand Soil

Sand soil is a soil type composed mainly of sand particles, a small amount of clay and silt particles, and low amounts, if any, of humus.

Example 2: Comparing Clay, Silt, and Sand Soils

Which component is present in larger amounts in silt soil than in sand and clay soils?

  1. Sand
  2. Clay
  3. Humus

Answer

We know that silt soil is a soil type composed of a mixture of gravel (small stones), sand, clay, silt, and larger amounts of humus than clay or sand soils.

Silt soil contains fewer sand particles than sand soil, so option A is incorrect.

Silt soil contains fewer clay particles than clay soil, so option B is incorrect.

Silt soil contains more humus than clay or sand soils.

So, the correct answer is option C: silt soil has larger amounts of humus than sand and clay soils.

We might think of soil as a dirty material that is not useful, but soil is very useful because it allows us to grow plants.

The differences in the compositions of clay, sand, and silt soils make them useful for growing different types of plants.

Here are some plants that grow best in clay soil.

Other plants, like these four types of fruits, grow best in silt soil.

Sand soil is suitable for growing plants that make tubers. Tubers are short underground stems, as shown in the picture below.

dug from the soil tubers of yellow potatoes with ripe large and small potatoes

Potatoes and sweet potatoes are both examples of plants that make tubers.

Plants that give fruits beneath the soil surface, like peanuts, also grow well in sand soil.

Example 3: Identifying Plants That Grow in Clay Soil

Different plants grow well in different soils. Look at these lists of plants.

List 1List 2List 3
Potatoes
Peanut
Sweet potatoes
Cotton
Sugarcane
Wheat
Strawberries
Pomegranates
Oranges

Which list shows plants that clay soil is best suited for growing?

Answer

Let’s begin by looking at list 1. List 1 contains potato and sweet potato. These are tuber-producing plants.

It also contains peanuts, a type of plant that grows fruits underneath the soil surface.

Both tuber-producing plants and plants that grow fruits underneath the soil surface are best suited to growing in sand soil.

The plants in list 2, cotton, sugarcane, and wheat, all grow best in clay soil.

The plants in list 3, strawberry, pomegranate, and orange, all grow best in silt soil.

So, the correct answer is list 2; clay soil is best suited to growing the plants in list 2.

Example 4: Identifying the Best Soil for Different Plants

Three friends name the type of soil they each have in their garden.

Who has the best soil for growing lemon and orange trees in their garden?

Answer

Dalia has clay soil in her garden.

Clay soil is best suited for growing plants like cotton, rice, and wheat, not oranges and lemons.

Seif has sand soil in his garden.

Sand soil is best suited for growing plants that grow tubers like potatoes, or plants that produce fruits under the soil surface like peanuts.

Mariam has silt soil in her garden.

Silt soil is well-suited to growing fruits like oranges and lemons, as well as strawberries and pomegranates.

So, the correct answer is Mariam; Mariam has the best soil for growing lemon and orange trees in her garden.

We learned that clay, silt, and sand soils are all made up of different particles.

They look and feel different from each other.

Some soils are granular, made up of small particles, and others are rocky, made up of larger particles.

Soils with smaller particles feel smooth, while soils with larger particles feel rough.

Clay soil has smaller particles than sand soil or silt soil. This means that clay soil feels the smoothest.

Silt soil has particles in between the sizes of clay soil particles and sand soil particles. This means that silt soil feels rougher than clay and smoother than sand.

Sand soil has larger particles than silt soil or clay soil. This means that sand soil feels the roughest.

Example 5: Describing Soil Textures

Different soils can have different textures. Which of the following describes soil texture?

  1. Smooth
  2. Rocky
  3. Rough
  4. Granular
  5. All of the answers are correct.

Answer

Soils can be described using the words smooth and rough. For example, clay soil is smoother than sand soil, and sand soil is rougher than clay soil.

So, options A and C are correct.

Soils can also be described using the words rocky and granular. Granular soil is made up of small particles while rocky soil is made up of larger particles.

So, options B and D are also correct.

Options A, B, C, and D are all correct, so the answer is option E; all of the answers are correct.

In this explainer, we have learned how to describe the compositions of different types of soil and identify plants that can grow in each.

Let’s recap the key points that we have learned.

Key Points: Types of Soil

  • Clay soil
    • is mainly made up of clay and silt particles with a small amount of sand particles and humus;
    • is good for growing plants like cotton, rice, wheat, sugarcane, and many vegetables;
    • is made up of smaller particles than silt soil and sand soil, so it feels more smooth.
  • Silt soil
    • is a mixture of gravel, sand, clay, and silt, and contains larger amounts of humus than sand or clay soil;
    • is good for growing plants like lemons, strawberries, pomegranates, and oranges;
    • has a particle size and a texture that are in between those of clay soil and sand soil.
  • Sand soil
    • is mainly sand particles with a small amount of clay and silt particles and low amounts, if any, of humus;
    • is good for growing tuber-making plants and plants that give fruits beneath the soil surface;
    • is made up of larger particles than clay soil and silt soil, so it feels the roughest.

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