1. Introduction to Soil Science

Soil science is the study of soil as a natural resource, including its formation, classification, mapping, physical, chemical, biological, and fertility properties, and its management for sustainable use.

2. Soil Formation

2.1. Factors of Soil Formation

  • Parent Material: The original rock or organic material from which soil develops.
  • Climate: Temperature and precipitation influence weathering.
  • Organisms: Plants, animals, and microorganisms contribute organic matter and aid decomposition.
  • Topography: Slope and landscape position affect drainage and erosion.
  • Time: Soil formation is a slow process, taking hundreds to thousands of years.

2.2. Soil Horizons

Soil forms in layers called horizons:

  • O Horizon: Organic matter (leaf litter, decomposed materials)
  • A Horizon: Topsoil, rich in minerals and organic material
  • E Horizon: Eluviation (leaching) layer, lighter in color
  • B Horizon: Subsoil, accumulation of leached materials (clay, iron)
  • C Horizon: Weathered parent material
  • R Horizon: Bedrock

Soil Horizons Diagram

3. Soil Properties

3.1. Physical Properties

  • Texture: Proportion of sand, silt, and clay
  • Structure: Arrangement of soil particles into aggregates
  • Porosity: Amount of pore space for air and water
  • Color: Indicates organic matter, minerals, and drainage

3.2. Chemical Properties

  • pH: Measure of acidity or alkalinity
  • Cation Exchange Capacity (CEC): Soil’s ability to hold nutrients
  • Nutrient Content: Essential elements (N, P, K, Ca, Mg, S, micronutrients)

3.3. Biological Properties

  • Microorganisms: Bacteria, fungi, actinomycetes
  • Fauna: Earthworms, insects, nematodes
  • Organic Matter: Decomposed plant and animal material

4. Soil Functions

  • Medium for Plant Growth: Provides nutrients, water, and support
  • Water Regulation: Controls infiltration, storage, and movement
  • Habitat: Supports diverse organisms
  • Nutrient Cycling: Decomposes organic matter, recycles nutrients
  • Engineering Medium: Foundation for buildings and roads

5. Soil Classification

  • USDA Soil Taxonomy: Orders, suborders, great groups, subgroups, families, series
  • World Reference Base (WRB): International system for soil classification

6. Surprising Facts

  1. Soil Contains More Organisms Than People on Earth: A single gram of soil can contain billions of microorganisms.
  2. Soil Is a Major Carbon Sink: Soils store more carbon than the atmosphere and all plant life combined.
  3. Soil Can Glow: Certain soils with high organic content or minerals show phosphorescence or fluorescence under UV light.

7. Case Studies

7.1. Soil Restoration in the Loess Plateau, China

Large-scale reforestation and terracing transformed eroded land into productive soil, improving food security and biodiversity.

7.2. Biochar Application in Tropical Soils

Biochar, a form of charcoal, is added to soil to improve fertility, increase water retention, and sequester carbon, as practiced in parts of the Amazon.

7.3. Urban Soil Pollution in Lagos, Nigeria

Rapid urbanization led to heavy metal contamination in soils, affecting food safety and public health. Remediation efforts include phytoremediation using local plants.

8. Mnemonic for Soil Horizons

“Only Ants Eat Bread Crumbs Regularly”

  • O: Organic
  • A: Topsoil
  • E: Eluviation
  • B: Subsoil
  • C: Parent Material
  • R: Bedrock

9. Latest Discoveries

9.1. Soil Microbiome and Climate Change

Recent research highlights the role of soil microbes in regulating greenhouse gas emissions. A 2022 study in Nature Microbiology revealed that specific microbial communities can increase soil’s ability to sequester carbon and reduce methane emissions, offering new strategies for climate mitigation.

Reference:
Zhao, M., et al. (2022). “Microbial community assembly and carbon cycling in agricultural soils.” Nature Microbiology, 7, 345–356. Link

9.2. Soil DNA Barcoding

Advances in DNA sequencing allow identification of soil organisms with high precision, enabling better understanding of soil biodiversity and health.

9.3. Smart Soil Sensors

Development of real-time soil sensors provides continuous data on moisture, nutrient levels, and microbial activity, improving precision agriculture.

10. Diagram: Soil Texture Triangle

Soil Texture Triangle

11. Glossary

  • Eluviation: Removal of dissolved or suspended material from a soil horizon.
  • Phytoremediation: Use of plants to remove or neutralize contaminants.
  • Biochar: Charcoal used as a soil amendment.
  • Cation Exchange Capacity (CEC): Soil’s ability to retain positively charged ions.

12. Summary Table

Property Description Importance
Texture Sand, silt, clay proportions Water/nutrient retention
Structure Aggregation of particles Root growth, aeration
pH Acidity/alkalinity Nutrient availability
CEC Nutrient-holding capacity Fertility
Organic Matter Decomposed material Soil health, structure

13. Additional Resources

End of Study Notes