Soil Design Challenge

Soil is defined as the naturally occurring, unconsolidated mineral or organic material at least 10 cm thick that occurs at the Earth’s surface and is capable of supporting plant growth (Source: sis.agr.gc.ca/cansis/taxa/cssc3/chpt02.html).

To understand the soil of an area, soil scientists (known as pedologists) take samples from many locations. These samples are part of a larger study called a soil survey. A soil survey is a carefully planned study of the soils in an area. The scientists examine, describe, classify and map the soils.

A soil profile is one part of a formal soil survey. A soil profile shows and describes the layers of the soil just below the surface of the earth. This profile is one tool used to classify the soils of the area. To create a soil profile, pedologists look at a cross-section of the land. In this cross-section, they can observe and describe the physical properties for each layer or horizon they see.

Soil Composition

Soil is all around us, it is also important to our daily lives. While many people merely
think of it as dirt (do NOT say this in front of a pedologist!), it is essential to us. Most plants
need soil to grow in, without it we wouldn’t be able to grow wheat (bread), vegetables, or fruit.

Soil Formation

If you could look below the Earth’s surface, you would see that soil is formed in layers (see photo and diagram above). Pedologists call these layers horizons. By studying soil horizons scientists can determine the age of the soil, how it was formed and its suitability for farming, construction or environmental projects. A soil profile has three horizons, from the surface downwards they are called A, B and C.

A horizon – is the top layer of soil (topsoil). It is the most fertile because of the organic matter which has accumulated from plant and biological activity. Full of nutrients, topsoil is the most productive layer for growing plants and supporting life. Earthworms, insects, microorganisms and plant roots live here.

B horizon – is the soil under the top layer (subsoil). Usually lighter in colour because it doesn’t contain organic matter, making it less fertile. This layer is rich in minerals but low in nutrients and organic matter which makes it less productive for plant growth. If topsoil is washed or stripped away, plants are forced to find nourishment in the subsoil.

C horizon – is the soil layer that lies under the subsoil and contains deposits of sand, gravel, pebbles, boulders and rocks. This is the original material, also called the parent material, from where the soil developed.

Under the C horizon is the bedrock - Solid rock that lies beneath the soil.