An Introduction to Soil

“Soil is the mixture of minerals, organic matter, gases, liquids, and organisms that together, support plant life”

Soil is the unconsolidated material that lies at the earth’s surface that has been altered over time.

Soil is not dirt! We get rid of dirt, but preserve soil!

Soil is made up of minerals (from rocks), air (lets gasses in and out of the pores in soil), water (keeps reactions proceeding/allows plants and organisms to grow), and organic matter (dead/decaying plant and animal matter). It is also known as the “skin of the Earth”, providing interfaces between the lithosphere, hydrosphere, atmosphere, and biosphere.

Soil, in the end, is a product of the climate, relief (topography, aspect, elevation, and slope), biotic interactions (organisms), and organic material (parent material) interacting over a period of time.

Much of the Earth’s surface is covered by soil, and life on Earth is completely dependent on it, aided with air and moisture.

Soils are constantly undergoing change by physical, chemical, and biological processes. This constant change over time has developed vertically layered structures from the top down (oldest at the bottom, youngest at the top), these are called horizons.

Each horizon is differentiated on the basis of colour, structure, texture, chemistry, and organic matter, among other variables.


The O-Horizon is the organic (humus) layer; This layer is dominated by large amounts of plant and animal residues that are in various stages of decay. This horizon is mainly found in forested areas.

The A-Horizon is the organics mixed with minerals, often referred to as “topsoil”.

The B-Horizon is the sub-soil, which reflects the characteristics of its parent material.

The C-Horizon is the parent material in sedimentary rocks, which is composed of large chunks of rock.

The R-Horizon is the parent material bedrock.

Soil has 6 main roles:

  • Medium for plant growth
  • Regulate water supplies (storage, supply, and purification)
  • Recycles raw materials
  • Modifies the atmosphere (nitrogen/carbon cycles)
  • Engineering medium – We build on it! (Also provides stability for tree roots)

Grow Calgary is committed to our soil program.

Good Soil = Good Food!