Components of Soil

Mineral soils consist of four major components:  mineral materials, organic matter, water, and air

1. Mineral Materials

     - sand, silt and clay are the 3 major components of the mineral fraction of soil

    - they account for 45%-50% of the total soil volume

    - sand and silt particles are derived from quartz and feldspar

    - gravel and sand can be seen with the naked eye

    - a magnifying glass is necessary to see silt particles

    - clay particles are derived from silica and aluminum oxides

2.Organic Matter

    - consists of dead and decaying plants and animals.

    - is critical for gardening success because:

    - improves the soil’s physical structure

    - holds and releases plant nutrients

    - increases the water holding capacity of the soil

    - increases beneficial organisms in the soil

3.Water and Air

    - are found in the pore spaces between mineral and organic components

    - account for about 50% of total soil volume

    - are essential for the growth of plant roots and soil microbes

    - dissolve most plant nutrients

Soil porosity is a measure of the pore space volume of a given soil:

    - sandy soils have large pore spaces which promote rapid drainage of water and leaching of nutrients and organic matter

    - clay soils contain tiny pore spaces which may impede root growth and water drainage

    - increasing organic matter increases the soil’s porosity and capacity to hold water

Air is pushed out when water comes into the soil from precipitation or irrigation of groundwater.

If air is unavailable to plant roots for too long, the plant suffers from lack of oxygen.


Some water is used by plants, some is lost through evaporation, and some moves so deep into the soil the plant roots cannot reach it.   

Soil Layers (Horizons)

Ontario soils have at least 3 distinct layers that differ in colour, texture, consistency, and structure.

  1. Surface Soil

        - contains most of the organic matter and plant roots

        - provides most of the nutrients and water to plants

    2. Subsoil

        - consists of small clay particles that are carried down by gravity and rainfall

        - is lower in organic matter

        - provides storage space for water and nutrients

        - helps regulate the soil temperature and air supply of plant roots

    3. Parent Material

        - is made up of decomposed rock characteristic of the bedrock

        - influences the soil’s texture, fertility, acidity, and depth

Soil Structure

In each textural class there is a range in the amounts of sand, silt, and clay that can

be present.

Most surface soils in Ontario fall into five textural classes.  Each class name indicates relative amounts of sand, silt and clay in the soil.

1. Silt loam

2. Loam

3. Silty clay loam 

4. Sandy loam

5. Clay Loam

Slide presentation can be downloaded in pdf format below.  

Dinah Wilson,
May 28, 2015, 4:45 AM
Dinah Wilson,
May 28, 2015, 4:47 AM
Dinah Wilson,
May 25, 2015, 10:43 AM