Soil Properties Study Notes

Soil Properties

Objectives

• Describe soil by physical, chemical, and biological properties.
• Distinguish among physical, chemical, and biological properties.
• Differentiate between homogenous and heterogeneous mixtures.

Key Terms

• Clay: Smallest soil particle.
• Sand: Largest soil particle.
• Silt: Intermediate sized soil particle.
• Soil Structure: Grouping of soil particles.
• Soil Texture: Relative percentages of sand, silt, and clay.
• Topsoil: Upper cultivated part of soil profile.
• Subsoil: Below topsoil, accumulation of clay.
• Tillage Pan: Compacted area from repeated plowing.
• Mottling: Color spots indicating drainage and aeration.

Soil Texture

• Permanent physical property defined by particle ratios (sand, silt, clay).
• Light Soils (coarse): Require less energy, dry faster, lower fertility.
• Heavy Soils (fine): Clay-rich, prone to compaction and water retention.
• Loamy Soils: Medium texture, most desirable for crops.

Soil Structure Types

• Platy: Thin horizontal sheets.
• Prismatic: Vertical columns without rounded tops.
• Block-like: Irregular cubes.
• Spheroidal: Rounded, often granular.

Soil Drainage

• Internal Drainage: Important for plant growth.
• Poorly drained = grey, improved = yellowish-brown, good = uniform bright color.

Biological Properties of Soil

• Living organisms include:
  • Microorganisms: Bacteria, fungi, nematodes, protozoa.
  • Macroorganisms: Earthworms, rodents, arthropods.

Chemical Properties of Soil

• Essential elements for growth depend on:
  • Availability, clay minerals, humus content, cation exchange, pH.

Mixtures

• Homogenous: Same type of soil particles (sand, silt, clay).
• Heterogeneous: Combination of different particle types.

Soil Management

• Improvement: Delay disturbance, use green manure, incorporate residues.
• Destruction Factors: Wet soil work, heavy equipment, deep repeated plowing, flooding.
• Use of no-till and reduced-tillage methods to minimize compaction.