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