Syllabus Edition

First teaching 2024

First exams 2026

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Factors Influencing Soil Formation (HL) (DP IB Environmental Systems & Societies (ESS))

Revision Note

Factors Influencing Soil Formation

  • There are a number of factors that affect how soil develops, including:

    • Climate

    • Organisms

    • Geomorphology

    • Geology

    • Time

Climate factors

  • Temperature variations: climate affects soil formation through temperature differences in various biomes

    • Tropical regions:

      • High temperatures and humidity promote rapid weathering and decomposition

      • This results in deep, nutrient-rich soils such as oxisols

    • Temperate regions:

      • Moderate temperatures and seasonal variations lead to well-defined soil horizons, like those found in brown earth soils

    • Polar regions:

      • Cold temperatures slow down biological processes

      • This results in thin, poorly developed soils with limited organic material

  • Precipitation levels: the amount and intensity of rainfall also influence soil characteristics

    • High rainfall:

      • In areas with heavy rainfall, leaching occurs, washing away nutrients and minerals from the topsoil

      • This leads to the formation of acidic soils like podzols

    • Low rainfall:

      • In arid regions, evaporation is greater than precipitation

      • This results in soil salinisation and the development of dry, nutrient-poor soils such as aridisols

Organisms

  • The presence of plants, animals, and microorganisms significantly influences soil formation

    • Plants:

      • Roots help break down parent material and contribute organic matter to the soil, enriching its nutrient content

    • Soil fauna:

      • Earthworms and other soil organisms aerate the soil and promote nutrient mixing, enhancing soil fertility

    • Microorganisms:

      • Bacteria and fungi decompose organic matter, recycling nutrients and improving soil structure

Geomorphology

  • Landscape features: the physical features of the landscape affect soil formation and characteristics

    • Slope:

      • Steep slopes may lead to soil erosion

      • Gentle slopes allow for deeper soil development

    • Aspect:

      • The direction a slope faces can influence temperature and moisture levels, affecting vegetation and soil types

      • For example, south-facing slopes in the Northern Hemisphere receive more sunlight and can support more vegetation than north-facing slopes

    • Drainage:

      • Well-drained areas often have drier soils with different characteristics compared to waterlogged regions, which may produce gley soils rich in organic matter

Geology

  • Types of parent material: the mineral composition of the parent material affects soil characteristics

    • Calcareous parent rock:

      • Soils derived from limestone or chalk are often rich in calcium carbonate, leading to fertile, alkaline soils like rendzinas

    • Volcanic parent rock:

      • Soils formed from volcanic ash, known as andosols, are typically very fertile due to the presence of minerals and nutrients

  • Weathering processes: the type of parent rock also influences how soils develop through weathering, erosion, and deposition

    • Chemical weathering:

      • Certain rocks, like granite, undergo chemical weathering, leading to the formation of nutrient-rich soils

    • Physical weathering:

      • Other rocks, like sandstone, break down through physical processes, resulting in sandy, less fertile soils

Time

  • Soil formation is a gradual process that takes time to develop

    • Soil maturity:

      • Older soils tend to have well-defined horizons and better-developed characteristics

      • This is due to long-term weathering and biological activity

    • Young soils:

      • In contrast, young soils may have less developed horizons and may be less fertile

      • They have had less time for organic matter accumulation and nutrient cycling to occur

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Alistair Marjot

Author: Alistair Marjot

Expertise: Biology & Environmental Systems and Societies

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

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