Concise Notes on Soil Architecture and Properties

Soil Color

• First observable characteristic
• Hue: Redness/yellowness
• Value: Lightness/darkness
• Chroma: Brightness
• Munsell Color Code: e.g., 10 YR 5/6 (Hue, Value, Chroma)

Soil Color Variability

• Influences:
• Organic matter (OM) content
  • Higher OM = darker soil
• Oxidation states of Iron (Fe)
  • Fe3+ = reds/yellows (well-drained)
  • Fe2+ = greys/blues (poorly drained)

Drainage Classes

• Well Drained: Depth to grey or mottles ≥ 30 inches
• Moderately Well Drained: 18-30 inches
• Somewhat Poorly Drained: 10-18 inches (mostly brown)
• Poorly Drained: 10-18 inches (mostly grey)

Soil Composition (A Horizon)

• Pore Space: 20-30% Air, 20-30% Water
• Organic Matter: 5%
• Mineral: 45%

Mineral Fraction

• Sand: 0.05 to 2 mm (gritty feeling)
• Silt: 0.002 to 0.05 mm (floury feeling)
• Clay: < 0.002 mm (sticky and crucial)

Soil Texture

• 12 texture classes based on sand, silt, and clay percentages
• Fine-textured soils retain water & nutrients better; coarse soils allow leaching.

Soil Structure

• Aggregates (peds) are arrangements of soil particles
• Types: Granular, Blocky, Platy, Columnar, Prismatic

Soil Consistency and Plasticity

• States: Solid, Semi-Solid, Plastic, Liquid
• Increases in moisture affect consistency and engineering properties

Soil Aeration

• Importance for gas exchange and oxidation-reduction potential
• Aerobic: High O2 (oxidation reactions)
• Anaerobic: Low O2 (slower breakdown)

Wetlands

• Water-saturated soils near the surface
• Characteristics:
• Wetland hydrology
• Hydric soils
• Hydrophytic plants

Soil Temperature

• Affects biological, physical, and chemical processes
• Influenced by solar absorption, moisture content, and soil cover

Management Practices

• Minimize tillage
• Maintain soil moisture
• Use organic matter (mulch, cover crops)
• Soil conditioners (e.g., gypsum) to prevent crusting.