1. Soil
Regolith – layer of rock and mineral fragments produced by weathering
Soil – part of regolith that supports plant growth

2. Soil Composition
Mineral matter, humus (decayed, organic material), air, water

3. Soil Texture Texture refers to % of particle sizes Sand (large size)
Silt
Clay (small size)
Loam (a mixture of all three sizes) is best suited for plant life

4. Soil Texture

5. Soil Formation The most important factors in soil formation are:
parent material
time
climate
organisms
slope

6. Soil Formation: Parent Material
Residual soil: parent material is the bedrock
Transported soil: parent material has been carried from elsewhere and deposited

7. Soil Formation: Time
• The longer a soil has been forming, the thicker it becomes

8. Soil Formation: Climate
Greatest affect on soil formation
hot/wet – thick/chemically weathered soil
cold/dry – thin/mechanically weathered soil

9. Soil Formation: Organisms
plants – main source of organic matter, acids from decay increase weathering
animals – burrow and mix materials (earthworms)

10. Soil Formation: Slope steep – more erosion = thin/nonexistent soil
flat – little erosion = thick soils

11. Soil Profile A Horizon – (topsoil) B Horizon – (subsoil) C Horizon -
mixture of mineral and organic matter, insects, fungi, microorganisms
 B Horizon – (subsoil)
fine clay particles leached out of A horizon
 C Horizon -
partially weathered parent rock