This document describes the typical horizons found in a mature soil profile. It explains that a mature soil profile contains O, A, B, and C horizons. The O horizon contains organic material like leaves and twigs. The A horizon is dark colored due to mixing with humus. The B horizon is the subsoil, containing materials leached from above. The C horizon contains partially weathered parent material and mineral particles.

1. SOIL HORIZONS Your Objective: Describe a mature soil profile. © Copyright 2004 - 2005. M. J. Krech. All rights reserved.

2. SOIL HORIZONS This is a typical mature soil profile. Notice the Horizons that are present in this profile: O, A, B, C What Horizons are missing from this picture?

3. O HORIZON The O Horizon contains layers of O rganic material, such as leaves, pine needles and twigs and decaying animal tissues.

4. A HORIZON The dark color of the A Horizon is from the mixing of Humus (Organic Matter) with weathered minerals.

5. E Horizon E Horizon: E stands for “ eluviation ,” which is the movement of dissolved or suspended materials out of the A Horizon. It is lighter in color than the layers above or below it.

6. B HORIZON B Horizon: Commonly called Subsoil . The illuviated zone, where containing soil materials leached from above. Color: yellow or red.

7. C HORIZON C Horizon: Partially weathered parent material and mineral particles are in this horizon.

8. R HORIZON R Horizon: Unaltered bedrock within a few feet of the surface. Common in Missouri. (Dolomite, dolostone, or limestone.) Typically requires blasting to dig through.

9. In the Real World: Soil Profiles are as different as People are different! Every state has dozens of Soil Profiles. Cole County has seven main soil profiles alone! Everyone one of them is different.

10. Can you identify the Horizons? A. B. C. D. E. F.

11. Can you identify the Horizons?

12. The End What is a typical mature soil profile? Write your answer on a scrap of paper and turn into your teacher. © Copyright 2004 - 2005. M. J. Krech. All rights reserved.