fundamentals of soil science exam 1

Definition of Soil:

Soil is the natural medium composed of mineral particles, organic matter, water, and air, supporting plant life.

Functions/Uses of Soil:

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• Plant growth medium

• Habitat for organisms

• Water filtration and storage

• Engineering foundation

• Nutrient cycling

What Can Be Learned from Studying Soil?

• Soil fertility

• Climate history

• Pollution levels

• Land use changes

Ecosystem Services Provided by Soil:

1. Plant Growth: Provides nutrients and anchorage for plants.

2. Water Holding & Cleansing: Retains and purifies water.

3. Decomposition: Breaks down organic material, recycling nutrients.

Soil as a Medium for Plant Growth:

• Root Characteristics: Roots anchor plants and absorb nutrients.

• Water Movement: Water moves through soil via capillary action.

• Nutrient Uptake: Roots absorb nutrients through diffusion, mass flow, and root interception.

Soil as an Engineering Medium:

• Used for roads, buildings, and agriculture.

• Threats: Erosion, compaction, and poor drainage.

Important Soil Nutrients:

• Macronutrients: Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S).

• Micronutrients: Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Molybdenum (Mo), Boron (B).

Soil Profile and Horizons:

1. O-Horizon: Organic matter.

2. A-Horizon: Topsoil, rich in minerals and humus.

3. E-Horizon: Leached layer, mostly sand and silt.

4. B-Horizon: Subsoil, accumulation of clay and minerals.

5. C-Horizon: Weathered parent material.

Soil Constituents:

• Mineral Matter: ~45%

• Organic Matter: ~5%

• Pore Space: ~50% (water & air)

Chapter 2: Soil Formation

Five Soil Forming Factors:

1. Parent Material – Source of soil minerals.

2. Climate – Influences weathering and organic matter.

3. Organisms – Contribute to decomposition and nutrient cycling.

4. Topography – Affects drainage and erosion.

5. Time – Longer formation leads to well-developed profiles.

Types of Rock & Their Formation:

• Igneous: Formed from cooled magma (e.g., granite, basalt).

• Sedimentary: Formed from compressed sediments (e.g., sandstone, limestone).

• Metamorphic: Altered by heat and pressure (e.g., marble, schist).

Weathering:

• Physical: Breakdown without chemical change (e.g., frost wedging).

• Chemical: Changes mineral composition (e.g., oxidation, hydrolysis).

Parent Material:

• Residual: Formed in place from bedrock.

• Transported: Moved by wind, water, ice, or gravity.

  • Alluvial: Water-deposited (sorted).

  • Glacial: Ice-deposited (unsorted).

  • Eolian: Wind-deposited (fine particles).

Effects on Soil Development:

• Temperature: Warmer climates accelerate weathering.

• Water: High rainfall leads to leaching.

• Living Organisms: Plants and animals mix and enrich soil.

• Human Impact: Farming, deforestation, construction alter soil properties.

Chapter 4: Physical Properties of Soil

Most Important Property:

• Soil texture affects water retention, aeration, and nutrient availability.

Soil Color:

• Components: Hue (color), Value (light/dark), Chroma (intensity).

• Measurement: Munsell Soil Color Chart.

• Indicators:

  • Red/yellow = oxidized iron (well-drained soil).

  • Gray/blue = reduced iron (poor drainage).

Soil Texture:

• Particle Sizes:

  • Sand: 0.05-2.0 mm

  • Silt: 0.002-0.05 mm

  • Clay: <0.002 mm

• Measurement Methods:

  • Field test: Ribbon test (hand feel).

  • Lab test: Hydrometer method (differential settling rates).

Stoke’s Law:

• Describes sedimentation rate of particles in a fluid.

Surface Area & Particle Size Relationship:

• Smaller particles (clay) have higher surface area, affecting water retention and nutrient holding.

Soil Structure Types:

1. Crumb: Loose and granular (good for plant growth).

2. Blocky: Irregular blocks (moderate drainage).

3. Platy: Thin horizontal plates (poor drainage).

4. Columnar/Prismatic: Vertical columns (often found in arid soils).

Factors in Soil Structure Formation:

• Electrostatic interactions, inorganic/organic binding agents, biological activity.

Density & Compaction:

• Particle Density: ~2.65 g/cm³ (constant).

• Bulk Density: Varies based on compaction and porosity.

Pore Space:

• Micropores: Hold water.

• Macropores: Allow air and water movement.

Other Key Terms:

• Shrink-Swell Clays: Expand when wet, shrink when dry.

• Thixotropy: Soil liquefaction under stress.

• 40 sec hydrometer test is enough time for sand to go to bottom

• 2 hours hydrometer is enough time for the silt and sand to separate