Soil is something many people look at on the ground, but might not consider how it gets there.
In this quick guide, we look at what soil is made of, how soil is formed, and how it develops over time.
Summary – Soil Makeup, Formation & Development
Soil is made of mineral particles, organic matter, air and water
The main factors that determine how soil forms are parent rock material, climate, landscape, living organisms and plant life, time, and the way the soil is managed
Because of the above factors, soil can be different in different parts of a country, and different parts of the world
What Is Soil Made Of?
All soils are all made of mineral particles, organic matter, air and water (sciencelearn.org.nz).
How Soil Is Formed, & How It Develops
There’s six key factors that determine how soil is formed and how it develops:
- Parent Rock Material
A key factor. Parent rock is the material lying underneath the soil. The minerals and properties of the parent rock are inherited by the soil, so the soil often has characteristics that it gets from the parent rock.
Parent rock material varies in different places around the world, hence why we get different soils in different places. Some are hard, some are soft, some have a lot of clay, whilst others have more sand, and so on.
Some parent material stays in the same place, whilst others are transported (washed, blown etc.) from one place to another.
The other key factor to how soil is formed.
Climate – rainfall and temperature in particular – are responsible for breaking down parent material over time.
Rain, snow, heat and cold (through expansion and contraction) all contribute to breaking down of the parent material.
Once the soil is formed, climate and the weather is responsible for the yearly development of the soil, such as how well minerals and salts can move through the soil.
- Landscape (also called Relief)
Landscape involves where the soil lays.
Soil on the top or in the middle of hills and inclines for example tend to erode and be shallower over time than soil at the bottom of inclines and hills. This is due to wind and soil erosion washing and blowing the soil down the incline.
- Living Organisms & Plant Life
A big part of the long term health and fertility of the soil as well as the development.
When living things die, they decompose and turn into organic matter and humus.
Microorganisms in the soil then break down or mix up that organic matter and make it available as nutrients for plant life. The roots of trees, plants and crops also get into the cracks in the soil and help make nutrients available.
It takes time for bedrock and parent material to break down and help soil form.
Further to that, it takes time for topsoil to develop from the break down of organic matter (500 to 1000 years for 1-2 cms in some places). Older soils are typically more fertile and deeper than younger soils.
- The Way The Soil Is Managed By Humans
The human factor that impact soil development is how it is managed.
Certain human activities, particularly agricultural and gardening activities, can be responsible for things like erosion, contamination, adding water or nutrients, adding and removing cover crops, and so on – and, all of these things can impact how the soil develops over time.
Why Soils Are Different To One Another Around The World, Or In Different Locations
The obvious answer is that the six factors listed above vary from place to place.
For example, parent rock material varies all around the world, and climate differs from location to location – just as two examples.
As the factors vary, the soils also vary.
- There are a range of factors contributing to soil diversity across the globe …
- Soils are the product of climate, organisms and topography, acting on parent (geologic) material over time.
- Thus the great diversity of geologic materials, geomorphic processes, climatic conditions, biotic assemblages and land surface ages in the United States is responsible for the presence of an enormous variety of mineral and organic soils.