Lecture Notes: Soil Formation and Erosion

Introduction to Soil

• Importance of Soil: Foundation for plant growth, water filtration, and various functions.
• Objective: Describe soil characteristics and formation.

What is Soil?

• Composition: Mix of geological and organic components.
  • Geological Components: Sand, silt, and clay.
  • Organic Components: Includes humus, nutrients, water, air, and living organisms.
• Humus: Decomposed organic matter, providing nutrients and structure.
• Nutrients: Ammonium, phosphates, nitrates critical for plant growth.
• Living Organisms: Earthworms, fungi, bacteria, aiding in nutrient recycling.

Roles of Soil in Ecosystems

1. Supports Plant Growth:
   • Anchors plant roots.
   • Provides water and essential nutrients (N, P, K, Mg).
2. Water Filtration:
   • Soil traps pollutants, clean water helps recharge groundwater.
3. Nutrient Recycling:
   • Decomposers break down organic matter, return nutrients.
4. Habitat:
   • Supports earthworms, fungi, bacteria, and other organisms.

Weathering and Erosion

• Weathering: Breakdown of rocks into smaller pieces.
  • Types: Physical (wind, rain), chemical (acids), biological (plant roots).
• Erosion: Transport of weathered rock particles.
  • Process: Detachment, movement, deposition.

Soil Formation

• From Below: Weathering of parent material/bedrock contributes minerals.
• From Above: Decomposition of organic matter adds humus.
• Factors Affecting Formation:
  1. Parent Material: Influences soil pH and nutrient content.
  2. Topography: Steep slopes may hinder formation due to erosion.
  3. Climate: Temperature and precipitation influence organic matter breakdown.
  4. Soil Organisms: Decomposers increase rate of soil formation.

Soil Horizons

1. O Horizon: Organic layer with plant material, traps moisture.
2. A Horizon (Topsoil): High in humus and minerals, most biological activity.
3. B Horizon (Subsoil): Contains clay, fewer nutrients, less organic matter.
4. C Horizon: Least weathered, resembles parent material.

Soil Degradation

• Loss of Topsoil: Due to tilling and vegetation loss, reduces productivity.
• Compaction: Machines/livestock compress soil, reducing pore space for water.
• Nutrient Depletion: Continuous cropping reduces soil fertility.