1. Introduction

Soil science is the study of soil as a natural resource, encompassing its formation, classification, mapping, physical, chemical, biological, and fertility properties. Soil is fundamental for terrestrial ecosystems, agriculture, water filtration, and carbon cycling.

2. Soil Composition

  • Mineral Matter: (~45%) Sand, silt, clay.
  • Organic Matter: (~5%) Decomposed plants/animals, humus.
  • Water: (~25%) Held in pore spaces.
  • Air: (~25%) Oxygen, nitrogen, COโ‚‚.

Soil Profile Diagram

Soil Profile Layers

Figure: Typical soil horizons (O, A, E, B, C, R)

3. Soil Formation (Pedogenesis)

  • Parent Material: Original rock or organic material.
  • Climate: Temperature, precipitation affect weathering.
  • Organisms: Microbes, plants, animals contribute organic matter.
  • Topography: Slope, elevation influence erosion and drainage.
  • Time: Soil formation is a slow process (hundreds to thousands of years).

4. Soil Classification

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

Major Soil Orders (USDA):

  • Alfisols
  • Andisols
  • Aridisols
  • Entisols
  • Gelisols
  • Histosols
  • Inceptisols
  • Mollisols
  • Oxisols
  • Spodosols
  • Ultisols
  • Vertisols

5. Physical Properties

  • Texture: Proportion of sand, silt, clay.
  • Structure: Arrangement of soil particles into aggregates.
  • Porosity: Volume of pore spaces.
  • Bulk Density: Mass per unit volume.
  • Color: Indicates organic matter, mineral content, drainage.

6. Chemical Properties

  • pH: Acidity/alkalinity; affects nutrient availability.
  • Cation Exchange Capacity (CEC): Soilโ€™s ability to hold nutrients.
  • Base Saturation: Proportion of soil bases (Ca, Mg, K, Na).
  • Salinity: Concentration of soluble salts.

7. Biological Properties

  • Microbial Biomass: Bacteria, fungi, archaea.
  • Fauna: Earthworms, insects, nematodes.
  • Root Interactions: Plant roots modify soil structure and chemistry.

Soil Microbial Diversity Diagram

Soil Microbes

8. Soil Functions

  • Plant Growth Medium
  • Water Regulation
  • Nutrient Cycling
  • Habitat for Organisms
  • Carbon Sequestration
  • Pollutant Filtration

9. Famous Scientist Highlight

Dr. Hans Jenny (1899โ€“1992):
Pioneered the quantitative study of soil formation and developed the state factor equation:
Soil = f(climate, organisms, relief, parent material, time)

10. Surprising Facts

  1. Soil contains more living organisms in a teaspoon than there are humans on Earth.
  2. A single gram of soil can contain up to 10,000 different species of microbes.
  3. Soil stores more carbon than the atmosphere and all plant life combined.

11. Ethical Issues in Soil Science

  • Land Degradation: Unsustainable farming, deforestation, and urbanization deplete soil fertility.
  • Contamination: Use of pesticides, heavy metals, and industrial waste can pollute soil and water.
  • Equity: Access to fertile land is uneven, affecting food security and livelihoods.
  • Bioprospecting: Commercial exploitation of soil microbes raises concerns about benefit-sharing.

12. Recent Research

Citation:
Rumpel, C., & Kรถgel-Knabner, I. (2021). โ€œSoil organic matter in the Anthropocene.โ€ Nature Reviews Earth & Environment, 2, 554โ€“569.
Link

Key Insight:
Recent studies emphasize the role of soil organic matter in climate regulation and highlight the impact of human activities on soil carbon stocks. Restoration practices are critical to mitigate global warming.

13. Future Directions

  • Precision Agriculture: Use of sensors, AI, and drones for real-time soil monitoring.
  • Soil Health Restoration: Regenerative farming, cover cropping, and reduced tillage.
  • Carbon Farming: Incentivizing practices that increase soil carbon sequestration.
  • Microbiome Engineering: Manipulating soil microbial communities to enhance fertility and disease resistance.
  • Digital Soil Mapping: Integrating satellite data and machine learning for global soil assessment.

14. Additional Resources

15. Quick Reference Table

Property Description Importance
Texture Sand, silt, clay proportions Water retention, fertility
pH Acidity/alkalinity Nutrient availability
CEC Nutrient holding capacity Plant growth
Organic Matter Decomposed biomass Structure, fertility
Microbial Biomass Living organisms Nutrient cycling

16. Soil Science and the Ocean

  • Soil runoff influences marine ecosystems.
  • Nutrient-rich soils can cause algal blooms and affect bioluminescent organisms.
  • Soil conservation helps maintain healthy coastal environments.

17. Conclusion

Soil science is pivotal for sustainable agriculture, climate change mitigation, and ecosystem health. Ethical stewardship and innovative research are essential for future generations.

End of Handout