Overview
The lecture covers the definition, formation, composition, importance, and classification of soils, with a detailed discussion of the soil profile and its horizons.
Introduction to Soil
- Soil is the thinnest, topmost layer of the Earth's crust formed by weathering of rocks.
- It is both a mixture of rock debris and organic material developing on the Earth's crust.
- Main soil components are mineral particles, humus (organic matter), water, and air.
- The actual amounts of these components vary by soil type.
- Soil is a renewable natural resource and a medium for plant growth and supports life.
Factors of Soil Formation
- Soil formation depends on relief/topography, climate, vegetative cover, parent rock, and time.
- Slopes affect how soil is transported and deposited.
- Climate influences soil development through rainfall and temperature.
- Older soils differ in composition and texture from newly formed soils.
- Vegetative cover protects soil from erosion.
Soil Profile and Horizons
- Soil is organized into vertical layers called horizons: O, A, E, B, C, and R.
- O Horizon: Organic layer, rich in decaying leaves, plant debris, and animal matter; also called the humus layer.
- A Horizon: Topsoil, rich in minerals and organic matter; most plant roots and biological activity found here.
- E Horizon: Eluviated or leached layer, light in color due to removal of minerals, nutrients, iron, and aluminum oxides by water; common in forests.
- B Horizon: Subsoil, where minerals and nutrients leached from topsoil accumulate; darker due to iron, aluminum, and clay.
- C Horizon: Parent material (regolith), made of partially broken down and weathered rock, lacks organic matter.
- R Horizon: Bedrock, solid unweathered rock beneath the soil profile.
Explanation of E Horizon Color
- The E horizon is light because clay, iron, aluminum oxides, and organic matter are removed by water, leaving sand and silt.
Key Terms & Definitions
- Weathering — The breakdown of rocks into smaller particles by natural forces.
- Humus — Decayed organic material in soil.
- Eluviation/Leaching — Removal of minerals and nutrients from soil by water.
- Regolith — Layer of loose, weathered rock above bedrock.
- Horizon — Distinct layer in the soil profile with unique properties.
Action Items / Next Steps
- Review and draw the soil profile diagram with labeled horizons (O, A, E, B, C, R).
- Prepare a short written explanation of why the E horizon is light in color.
- Optional: Watch the "Seaspiracy" documentary for insights into marine pollution and environment.