Soil Systems Notes

Soil Systems

The Soil as a Living System

• Soil Trophic Levels
• Nutrient Cycling
• Ecological Spheres Review

Organic Matter

• Waste, residue, and metabolites from plants, animals, and microbes contribute to the organic matter in the soil.

Soil Food Web

• Includes nematodes (root-feeders, fungal and bacterial feeders, predators), arthropods (shredders, predators), fungi (Mycorrhizal fungi, saprophytic fungi), bacteria, protozoa (amoebae, flagellates, and ciliates), earthworms, and other animals (birds).

What is Soil?

• Healthy soil is a mixture of minerals/rock particles, humus, air, water, and micro-organisms.
• Loam is soil that is composed of sand, silt, and clay in roughly a 2:2:1 ratio.

Components

• Medium for plant growth
• Habitat: Soil ecosystems are diverse.
• Regulatory service: Water retention/reservoir.
• Supporting service: Nutrient cycling (organic biomass → detritivores/saprotrophs → nitrogen…).
• Provisional service: Use in housing (mud bricks), farming/gardening, landscaping, etc.

Soil Texture

• Sand (40%):
  • 0. 05 - 2 cm particles
  • Fast draining and quick drying
  • High percolation
  • High air space
  • Productivity: low
• Silt (40%):
  • 0. 002 - 0.05 cm particles
  • Medium water retention
  • Medium percolation
  • Medium air space
  • Productivity: medium
• Clay (20%):
  • < 0.002 cm particles
  • Can become sticky, easily waterlogged
  • Low percolation
  • Little air space
  • Productivity: medium - low

Soil Texture Triangle

• A graphical representation used to determine soil texture based on the percentages of sand, silt, and clay.

"Movement" in the Soil

• Biological mixing of nutrients and inorganic material.
• Movement of water (and minerals in water) due to percolation/infiltration.
• Uptake of nutrients by plants.
• Soil erosion by wind/water.
• Sediment deposition.

Transfers

• Decomposition of organic matter/detritus by decomposers.
• Weathering of parent material resulting in the increase of inorganic matter.
• Nutrient cycling example of carbon/nitrogen/phosphorus.
• Respiration by soil organisms.

Transformations

Soil Formation Stages

1. Soil Begins to Form
2. Simple Organisms
   • Organic Matter
   • Disintegrating Rock
   • Bedrock/Parent Material
3. Horizons Form
   • Organic Matter
   • Mineral Particles
   • A horizon
   • C horizon
   • Bedrock/Parent Material
4. Well-developed Soil
   • Organic Matter
   • Mineral Particles
   • A horizon
   • B horizon
   • C horizon
   • Bedrock

Ecological Succession

• Cultivated: 6 years, 16 years, 37 years
• Boreal forest

Soil Horizon Model

• O - Organic Matter
• A - Top Soil
• B - Subsoil
• C - Parent Rock
• R - Bed Rock

Soil Horizons

• Organic Matter (O):
  • Litter layer of plant residues.
  • In relatively undecomposed form.
• Surface Top Soil (A):
  • Layer of mineral soil with the most organic matter accumulation and soil life.
  • This layer is depleted of iron, clay and calcium, organic compounds, and other soluble constituents.
• Subsoil (B):
  • This layer accumulates iron, clay, aluminum, and organic compounds.
  • This process is known as illuviation.
• Parent Rock (C):
  • Layer of large unbroken rocks.
  • Little to no root penetration.
• Bedrock (R):
  • The parent material in bedrock landscapes.
  • Largely continuous masses of hard rock that cannot be excavated by hand.
  • Soils formed in situ will exhibit strong similarities to this bedrock layer.

Inputs & Outputs

INPUTS

• Rock weathering
• Atmospheric input
  • Lighting → N (Nitrogen)
  • Precipitation → S (Sulfur), Na (Sodium), Ca (Calcium), Cl (Chlorine)
• Biological processes
  • N-fixation (bacteria)
  • Animal residues
  • Decomposition

OUTPUTS

• Erosion
  • Includes crop removal & grazing
• Leaching
• Gaseous Losses
  • Wet, anaerobic soil
  • N (Nitrogen) especially

Inputs & Outputs (Diagram)

• Decomposition, weathering, and nutrient cycling
• Gain from - Precipitation, Weathering
• Loss by - Runoff, Leaching
• Biomass Pathway, Litter (L), Soil (S), Decay Pathway, Uptake Pathway

Soil Formation

• Soil formation is dependent on:
  • Climate: Precipitation/temperature determines the vegetation type and rate of decay; weathering (freeze-thaw cycles).
  • Organisms: Breaks down organic matter and mix it into the upper layers of the soil.
  • Relief: Elevation, aspect of the slope (direction it faces) and the angle of the slope.
  • Geology: The original/parent material that the soil develops from. (Usually bedrock or lake/glacial till that has been laid down on top of the bedrock.)
  • Time: Soil formation is a long and slow process; therefore, it is considered a non-renewable natural capital. The amount of time the soil has had to form will affect its characteristics.

Soil Orders to Know

• Mollisols
• Alfisols
• Oxisols
• Gelisols

Additional Resources

• Soil Type Global Distribution (Map) - USDA Natural Resources Conservation Service
• Dig It! Secrets of Soil (Interactive) - Smithsonian Online Exhibit
• How Soil is Created (Video) - 59 Degrees
• From Dirt to Lifeline (Video) - TEDTalk
• Soil Basics (Website) - Soil Science Society of America