Soil Horizons Explained

Friday, June 26, 2020





Why does my dog Rollins dig soil?

Soil is all around us and my dog Rollins loves to dig in soil.

You walk on grass rooted in the soil and eat food grown in soil.

Plants and trees need soil to grow but what is soil composed of?


If you look at a chart of soil you will see that soil is made up of.

  • 45% Minerals
  • 5% Organic matter like decaying plants and animals
  • 25% Water
  • 24% Air
You can also study soil by looking at the soil profile and the soil horizon.

A vertical layer of soil that shows all of the different layers is called the soil profile.

Much like your profile on facebook tells others all about you, the soil profile tells others all about the soil.

A soil horizon is each individual layer of the profile. Each layer has different physical properties.

The horizon layers are o a e b c r

O also called litter is composed it contains dead leaves, twigs, sticks, fallen trees 
The O horizon is thin in some soils, thick in others, and not present at all in others.

A also called topsoil contains rich organic matter along with some minerals. This layer contains decomposers. The decomposers perform the task of breaking down plants and animals. The remains of these plants and animals create a mixture called humus which is a dark, organic material that forms in soil when plant and animal matter decays.

E also is known as the Eluviated layer, is created when water moves down the soil substances and is removed and pulled out in this layer resulting in a concentration of sand and silt particles composed of quartz or other resistant materials.  This layer may be missing in some soils

B  also called Subsoil is lighter in color, many times reddish or brownish in color because it has less humus. It is a zone of accumulation where materials like clay collect from the movement of water downward.

C  also called Parent material contains much of the material that the soil was originally made from. It also contains rock fragments. Weathering breaks down this parent rock into smaller and smaller pieces of rock. This layer is most often light in color.

R also called Bedrock  A mass of rock such as granite, basalt, quartzite, limestone or sandstone that forms the parent material for some soils.

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