Soil Horizons Quiz

Which soil horizon is made up of fresh and partially decomposed organic material such as leaves and twigs?

• A horizon

• B horizon

• O horizon

• C horizon

Which horizon is known as “topsoil” and contains the most nutrients and biological activity?

• O horizon

• A horizon

• B horizon

• C horizon

What gives the A horizon its dark color?

• Clay

• Organic matter (humus)

• Iron oxides

• Sand

Which horizon is often called the subsoil and is where minerals like clay and iron accumulate?

• A horizon

• B horizon

• C horizon

• R horizon

Which horizon is made of partly weathered rock that is the source of mineral particles?

• C horizon

• A horizon

• O horizon

• B horizon

Which horizon is solid, unweathered bedrock?

• R horizon

• B horizon

• C horizon

• O horizon

True or False: The O horizon contains no mineral material.

• True

• False

Which horizon supports most plant roots?

• A horizon

• B horizon

• C horizon

• R horizon

As you move deeper into the soil profile, organic matter generally:

• Increases

• Decreases

• Stays the same

• Disappears completely

Which horizon acts as the main zone of plant growth and nutrient cycling?

• O horizon

• A horizon

• B horizon

• C horizon