Soil Notes

ABIOTIC FACTORS

• Abiotic factors include soil.

Objectives

• Define soil.
• Explain how soil is formed.
• Identify the components of topsoil.
• Compare three types of soil (sand, clay, and silt).
• Compare the water-holding capacity of sand, clay, and loam.

WHAT IS SOIL?

• Soil is a mixture of minerals, organic matter, air, and water.

HOW IS SOIL FORMED?

• Soil is formed from the weathering of rocks.
• Physical Weathering:
  • Water
  • Wind
  • Ice
  • Gravity
• Chemical Weathering:
  • Rust
  • Acid Rain
• Biological Weathering:
  • Roots
  • Lichen
  • Animals & Insects
  • Humans

SOIL PROFILE

• Components of topsoil will separate based on:
  • Density
  • Particle size
• The components include: humus, water, clay, silt, sand, gravel

COMPARING SAND, SILT AND CLAY

Clay

• Smallest particle size (less than $0.002mm$).
• Highest mineral content.
• Particles are tightly packed.
• Lowest air content.
• Highest water-holding capacity.

Silt

• Particle sizes are between $0.002mm$ to $0.02mm$.
• Medium air and mineral content.
• Medium water-holding capacity.

Sand

• Largest particle sizes (between $0.02mm$ to $2mm$).
• Lowest water-holding capacity.
• Lowest mineral content.
• Highest air content.

Other Soil Components

• Gravel has particle sizes greater than $2mm$.
• Humus is the organic matter found in topsoil.
• It improves the mineral and water content of the soil.

What is loam?

• Loam is a mixture of sand, silt, and clay with lots of organic material (humus).

Water Holding Capacity

• The volume of water a soil can hold (retain).
• Can be determined by the:
  • Size of the particles
  • Amount of space between the particles
  • Air content of soil
  • Capillarity

Calculating Water Holding Capacity

• $Volume : of : water : retained = volume : of : water : added – volume : of : water : drained$