Soil Science

Soil is a bunch of different mixtures which include things like air, organic matter, minerals, water and all kinds of dead and decaying plant and animal organisms.

The soil is what forms the land that we walk on and the land that we plant things on.  Sometimes, people call the soil the “skin of the Earth.”

Map of global soil regions from the USDA

Is Soil Important?

Soil is very important for both people, plants and animals.  Soil helps to give our plants life and the life of our plants helps people and animals to live.

Soil also helps our atmosphere.  Soil helps the atmosphere by releasing oxygen and taking in carbon dioxide.

Soil helps living things because it gives them a place to live and a place to grow.


The nutrient cycle is also helped by soil.  Soil helps to cycle the nutrients through the nitrogen cycle.

Water is also helped by soil because water is filtered and cleaned when it runs through the soil.

What is the Difference Between Dirt and Soil?

Dirt is soil that has lost all of the characteristics of soil and that has lost much of the minerals and organic matter.

Dirt is the stuff that makes us dirty when we are outside and what we track in on our shoes and on our clothing.

Soil and Our Ecosystem

Soil is very important for our ecosystem because it helps places such as:

  • Prairies
  • Farms
  • Marshes
  • Forests

What Does Soil Do?

There are seven different things that soil does that are important to our world.  Here is a list of important things soil does:

  • Helps plants and trees to grow.
  • Takes in gases such as carbon dioxide and releases healthy gases.
  • Gives a place for plants and animals to live.
  • Helps to hold in water and to make water cleaner.
  • Recycles the nutrients so that living things can use the nutrients again and again.
  • Helps to build foundations, roadways, dams and other areas.
  • Filters water.

Layers of Soil

There are different layers of soil and each soil has different horizons.  The horizons are called A, B, C, E, R and O.  All soil has three horizons; A, B, C and some have the fourth horizon O.

Horizon O

The horizon O is the organic soil horizon.  This is called organic or humus.  This is where there is a lot of organic matter such as animals and leaves that are dead and decaying or decomposing.

The O layer is a thin layer on some soil areas and is thick on other soil layers.

Horizon A

Horizon A is called the topsoil.  This is where most of the minerals are.  This is a good place for animals like worms to live because there are healthy minerals here.

Horizon E

The next level is Horizon E.  Horizon E is called the eluviated layer.  This layer is where there is clay and minerals and sand and salt and other sediments.  Some of the minerals are not found in this layer but is sometimes found in soil that is older.

Horizon B

Horizon B is the layer of soil that is called the subsoil.  This is the layer where there are good minerals that have leaked down from the top layers.  Some of the minerals from A and E have settled to this horizon.

Horizon C

Horizon C is called parent material.  This is where things that fall on the soil of the Earth started.

Horizon R

Horizon R is bedrock.  This is where there are rocks such as:

  • Granite
  • Sandstone
  • Limestone
  • Quartzite
  • Basalt

In this level, it forms the material for some soil, but this level is not considered soil at all.  If this is found in soil, it is always found under Horizon C.

How Was Soil Formed?

Some soil is thousands of years old because it can take thousands of years just for one inch of soil to form.  Time is the most important part of soil, but these other things help to form it as well:

  • Animals
  • Bacteria
  • Fungi
  • Topography
  • Parent Material
  • Climate

Animals, Bacteria, Fungi

These things are living organisms that help to make up soil.  These things live and then die and decay and they help to make soil form.


The topography or elevation of the land can help to make the land slope so that soil can form.

Parent Material

Parent material is where soil starts to form.  This is minerals and rocks that form a layer.


The climate can help soil to form.

Characteristics of Soil

Soil has many characteristics that make it soil.  Some of these include:

  • Texture
  • Temperature
  • Density
  • Color
  • Consistency
  • Porosity
  • Structure


The texture of soil is one of the most important characteristics.  The texture can tell if the soil is going to be able to hold water or not or if things will be able to be planted in it.

If the soil is grainy or has a lot of sand, it is more likely to hold less water.

When sand is more like clay, it can hold more water and it is better soil to plant things in.


When minerals move down the layers of soil, this is called leaching.

What is Soil Made From?

Even though soil is made from a lot of different things, it is mostly made of:

  • Oxygen
  • Carbon
  • Iron
  • Aluminum
  • Silicon

Kinds of Soil

There are basically three different types of soil:

  • Sand
  • Silt
  • Clay


Sand is the part of the soil that has larger particles.  This soil is rough and scratchy.  The sand has very few nutrients but the great thing about it is that it gives the plants drainage.


Silt is a type of soil that has medium particles.  This kind of soil feels smooth and can turn into a powder.  This soil holds a lot of moisture and has many nutrients.


Clay is a smoother soil that has very small particles.  It has a lot of nutrients, but it does not allow water to drain through it easily.  Even though clay is not the best to plant in, because it is so sticky when it is wet, it can help people to have something to build with.

Animals in the Soil

The soil is known to have a lot of animals and creatures in it.  These creatures help the soil just like the soil helps these creatures.  Some of these include:

  • Earthworms
  • Ants
  • Fungi
  • Gophers
  • Turtles
  • Any animal that burrows under the ground is considered to live in the soil.

Other things that live in the soil are called decomposers.  Decomposers means that they help to break down things that are not living into small pieces.  This can be dead animals or plants that are no longer alive.  The decomposers do this so that the plants can absorb the nutrients.

Without soil, animals would not be able to have anything to eat and that means that humans would not have food to eat either.

Plants of the Soil

Plants need many things to help them to grow such as sunlight, food, carbon dioxide and more.  Plants also need soil.  Some other things that plants need to grow are:

  • Nitrogen
  • Magnesium
  • Copper
  • Phosphorus
  • Potassium

Most of these minerals are found in the soil.  All plants and trees need soil in order to grow.  This is the area of the land that the plant is able to dig its roots in so that it can get water and nutrients.


The study of soil is called pedology.  A person who studies soil is called a pedologist.

How Does Climate and Weather Help to Make Soil?

When there is a lot of heat or a lot of cold, it causes rocks to expand and to contrast.  This means that they get bigger and smaller.  When this happens, it can cause rocks to break down to smaller rocks.  Soon, the rocks will get so small that they can turn into soil.

Can Soil Be Harmed?

Soil can be harmed by things that people do such as leak chemicals on the ground or use pesticides in their gardens.  This can cause the soil to become contaminated or bad.  When this happens, the bad stuff in the soil can get to the water system and cause people and animals to get sick.

Soil can also be harmed when there is a lot of rain or a lot of wind.  These things can cause soil to wash away or blow away and cause farmers not to be able to plant things.

How Can People Help Save Soil?

People can help to save soil by buying organic vegetables.  Organic vegetables and fruits are vegetables and fruits that are grown without any pesticides.

People can also make their own organic gardens.

Pulling weeds can help keep the soil healthy.

Composting is a great way to save the soil.  Composting means to recycle things that can go back into the ground like banana peels and potato peels.

More Facts About Soil:

  • Bacteria is found in all soil but if a soil is rich soil, it will have millions of bacteria in it.
  • The best soil to grow crops is the top layer.  The layers of soil that are underneath are sometimes grainy and sandy.
  • When a volcano erupts and it settles down, this soil is very rich in minerals.
  • Quicksand is soil that has water underneath the sand.
  • Soil has more living things in it than many other things.

What Did You Learn?

  • What is soil?
    Soil is the area of ground where things can be planted.
  • Does soil have nutrients?
    Soil is full of minerals and other nutrients.  Soil gets these from animals and plants that have decayed and left nutrients behind.
  • Is soil just one layer?
    There are many different layers of soil and each layer has an important role for keeping soil safe.
  • What is good about soil?
    Soil is good because it allows animals and insects to have a home, it helps to clean out our water and filter our water and helps things to be able to be grown.
  • Are there different types of soil?
    Yes.  There are three main types of soil and these are sand, silt and clay.