Week 3 - Topic 4 - Soil Profiles Flashcards
What is a soil profile?
An exposed vertical section cut down through the soil
The layers in a soil profile are called horizons.
What are the naturally occurring layers in a soil profile called?
Horizons
Where does most biological activity occur in a soil profile?
At the top where there is more air, water, and organic matter
What is the O Horizon primarily made of?
Organic matter accumulated on the surface
What are the two sub-types of the O Horizon?
- O1: Undecomposed organic matter
- O2: Decomposed organic matter (humus)
What is the A Horizon also known as?
Topsoil
What characterizes the A Horizon?
Surface mineral horizons with maximum organic material accumulation
What are the sub-types of the A Horizon?
- A1: Near surface with organic matter accumulation
- A2: Less organic matter, zone of leaching
What is the B Horizon known as?
Subsoil
Describe the texture of the B Horizon.
Finer texture than topsoil, high clay content
What are the sub-types of the B Horizon?
- B1: Zone of maximum deposition from A horizon
- B2: May show mottled colors indicating drainage conditions
What does the C Horizon consist of?
Layers below subsoil made of parent material
What are the sub-types of the C Horizon?
- C1: Weathered parent material
- C2: Unweathered parent material
What is the D Horizon?
Bedrock that may be unrelated to parent material and soil above
What are the key indicators of a natural soil profile?
- Texture changes
- Color interpretation
- Structural changes
- Additional indicators
How does texture change in a soil profile?
Coarser texture at top, gets finer with depth
What color indicates good aeration and drainage in the B Horizon?
Light brown/red
What smell indicates well-aerated, humus-rich soil?
Aromatic/fresh/earthy
What are common physical disturbances that affect soil profiles?
- Grading/levelling
- Cut and fill
- Raised levels
- Compaction
What are signs of disturbance in soil profiles?
- Unnatural texture changes
- Unnatural color changes
- Buried organic matter layers
What is a common effect of soil disturbance?
Poor water infiltration
What is a buried profile?
Created by levelling with fill, leading to perched water tables
What problems are associated with an inverted profile?
- Poor aeration
- Poor structure
- Reduced organic matter
What should be assessed when examining topsoil?
- Depth
- Texture
- Structure
- Color
What is a characteristic of a natural Sydney soil profile?
Organic matter on top with coarse to fine texture progression
