IBESS Topic 5.1: Introduction to Soil Systems

Key Concepts

• Soil System as a Dynamic Ecosystem

  • Inputs: Organic material (leaf litter), inorganic material from parent material, precipitation, and energy.
  • Outputs: Uptake by plants, soil erosion.
  • Storages: Organic matter, organisms, nutrients, air, and water.
  • Transfers: Biological mixing, translocation (movement of soil particles in suspension), leaching (minerals dissolved in water moving through soil).
  • Transformations: Decomposition, weathering, nutrient cycling.

• Soil as an Ecosystem

  • Soil is a complex ecosystem comprising minerals, organic material, gases, and liquids.
  • Provides habitats for animals and plants.
  • Acts as a thin bridge (petosphere) between biosphere and lithosphere.
  • Influenced by atmosphere, hydrosphere, lithosphere.

Ecosystem Services Provided by Soil

• Climate regulation
• Nutrient cycling
• Habitat for organisms
• Food regulation
• Source of pharmaceutical and genetic resources
• Foundation for human infrastructure
• Provision of construction materials
• Cultural heritage
• Provision of food, fiber, and fuel
• Carbon sequestration
• Water purification and soil contaminant reduction

Components of Soil

• Mineral Particles
  • Derived from underlying rock
  • Soluble and insoluble rock particles
  • Contains mineral salts (nitrogen, phosphor, potassium, sulfur, magnesium)
• Organic Matter (Humus)
  • Dark color, returns minerals and nutrients
  • Absorbs and retains water
• Water
  • Dissolves mineral salts, moves nutrients
  • Causes leaching and salinization
• Air
  • Provides oxygen for respiration of soil organisms and plant growth

Soil Organisms

• Soil invertebrates break down organic material.
• Microorganisms decompose particles, recycle nutrients.
• Large animals (e.g., moles) mix and aerate soil.

Soil Profile (Horizons)

• O Horizon: Partially decomposed organic matter.
• A Horizon: Topsoil, contains humus.
• E Horizon: Zone of leaching.
• B Horizon: Subsoil, accumulation of iron, aluminum, clay.
• C Horizon: Weathered parent material.
• R Horizon: Bedrock.

Soil Texture and Composition

• Particle Sizes
  • Sand: 0.05 to 2 mm
  • Silt: 0.002 to 0.05 mm
  • Clay: <0.002 mm
• Loam: Balanced mix of sand, silt, clay (ideal for plant growth)

Soil Quality Factors

• Porosity: Space between particles, affects permeability.
• pH: Affects nutrient availability, soil bacteria, structure.

Soil and Primary Productivity

• Soil quality influences productivity.
• Fertile soil contains necessary nutrients and has good structure.
• Importance of sustainable practices to maintain soil as a non-renewable resource.

Summary

• Soil systems are complex dynamic ecosystems.
• Understanding soil systems helps in sustainable management and conservation.

Resources

• Slides by Dr. Nina Markham.
• IBESS textbook (hardback/online sources).