Introduction - Environmental Soil Science (Notes)

What is soil? Perspectives from different disciplines

  • Geologists (Earth scientists)

    • Soil is the upper loose layer of the earth; defined differently by discipline but generally as loose, unconsolidated, weathered material on the surface, distinct from bedrock.
    • Focus areas for geologists:
    • How human activities influence soil (land use, pollution, landslide hazards).
    • Relationship between soil and the rock below for mineral, oil, and groundwater exploration.
    • The geological history of the Earth.
    • For geologists, soil = loose, unconsolidated, weathered material on the surface, distinct from bedrock.

  • Civil engineers / Construction engineers

    • Definition centers on the physical characteristics of soil in relation to construction projects.
    • Key focuses include:
    • Soil composition
    • Water content and permeability
    • Expansion and contraction properties
    • Bearing capacity
    • Engineers may define soil as the foundation material for buildings and engineering structures.

  • Ecologists

    • Study the interaction between living things and their environment.
    • Living organisms and the physical environment form an ecosystem (aquatic or terrestrial).
    • Examples of ecosystems: forests, grasslands, deserts, coastal areas, ponds, lakes, etc.
    • For ecologists, soil is the foundation of the terrestrial ecosystem.
    • Emphasis on objective conservation and ecosystem health.

  • Agricultural scientists

    • Study the interaction between plants, soils, livestock, and their environment (an agroecosystem).
    • Focus on enhancing plant and animal production.
    • Soil is the upper loose layer covering most land where plants grow.
    • Functions of soil include:
    • Anchoring plants
    • Supplying air to roots
    • Supplying water and nutrients to plants

Soil functions and ecosystem services

  • Soils deliver ecosystem services that enable life on Earth.

  • Major soil functions and services include:

    • Carbon sequestration
    • Provision of food, cultural heritage, fibre and fuel
    • Water purification and soil contaminant reduction
    • Climate regulation
    • Nutrient cycling
    • Habitat for organisms
    • Provision of construction materials
    • Source of pharmaceuticals and genetic resources
    • Flood regulation
    • (Other illustrative notes from the infographic context: soil supports biodiversity, nutrient storage, and material resources.)

  • 2015: International Year of Soils (FAO context)

    • Infographic highlights: soil provides multiple services including nutrition, water regulation, climate regulation, habitat, and material resources.

Soils in agriculture

  • Agriculture focuses on plant and animal production in a sustainable manner.
  • Plant products are used for food, feed, clothing, and biofuels.

Plants, production systems, and growing methods

  • The primary producers are plants; most plants are grown in soil.
  • Some plants can be grown in water (hydroponics).
  • Hydroponics: growing plants in water.
  • Aeroponics: growing plants suspended in air with mist on roots.

Global land use for food production (overview of the data visual)

  • Earth's surface distribution (Our World in Data):
    • Land: 29% of Earth's surface (~149 million km²).
    • Ocean: 71% (~361 million km²).
  • Habitable land: 71% of Earth's surface (~104 million km²).
  • Land use within habitable land:
    • Agriculture: ~50% of habitable land (~51 million km²).
    • Forests: ~37% (~39 million km²).
    • Shrubs: ~11% (~12 million km²).
  • Agricultural land specifics:
    • Agricultural land includes grazing land and arable land used for feed production: ~40 million km² (grazing + feed crops).
    • Excluding feed: ~11 million km².
  • Diet and calories:
    • Global calorie supply: ~18% from meat and dairy; ~83% from plant-based foods.
    • Global protein supply: ~37% from meat and dairy; ~63% from plant-based foods.
  • Other land categories:
    • Urban and built-up land: ~1%
    • Freshwater: ~1%
    • Glaciers and barren land: notable fractions (e.g., deserts, salt flats, exposed rocks, beaches, dunes).
  • Note: These figures come from FAO data and Our World in Data (Licensed CC-BY).

Population growth, food security, and the Green Revolution

  • Thomas Malthus (1798): Famous remark on population dynamics:
    • "The power of population is so superior to the power of the earth to produce substances for man that premature death must in some shape visit the human race."
  • The Green Revolution (Dr. Norman Borlaug):
    • Development and dissemination of high-yielding, disease-resistant semi-dwarf wheat varieties.
    • Initiatives in the 1960s to transfer agricultural technologies to developing countries.
    • Borlaug is known as the father of the Green Revolution and won the Nobel Peace Prize in 1970.
  • Question framing: Can the world feed ten billion people in the 2050s? (Linking Malthusian concerns with technological progress.)

Yield and the breeding question: arable land versus yield per area

  • Can we increase arable land and/or the yield per unit area to feed a growing population?
  • Yield is typically expressed as tonnes per hectare ( frac{t}{ha}).
  • Key reference: Ray et al. (2017), Agrifood Atlas (data visualization and synthesis).

Harvest index (HI), biomass partitioning, and historical trends

  • Harvest index (HI) definition:
    • HI = \dfrac{Grain\ yield}{Total\ plant\ biomass}
    • It represents the fraction of total biomass allocated to the harvested product (grain).
  • Historical patterns (example timeline from the slides):
    • HI values over time show improvement with breeding and agricultural practices:
    • Pre-1900: HI ≈ 0.41
    • 1900–1940: HI ≈ 0.43
    • 1941–1972: HI ≈ 0.48
    • >1972: HI ≈ 0.58
  • Additional related metrics (conceptual):
    • Grain-to-shoot ratio and straw-to-shoot ratio reflect biomass partitioning between grain and vegetative parts.
    • These ratios have shifted over time toward greater grain allocation with modern varieties and management.
  • Conceptual takeaway:
    • Modern breeding and management aim to increase HI, i.e., increase the proportion of biomass that becomes grain, without sacrificing total yield or plant health.

Resource use efficiency and crop management

  • Improving resource use efficiency among crops:
    • Plant shoots compete for resources (light, water, nutrients).
    • A plant with fewer shoots can channel more resources to grain, increasing yield.
    • Manual branch removal (pruning) is a common practice in horticulture to reduce competition and improve yield.
  • Implication: Optimizing plant architecture can enhance yield and resource use efficiency.

Historical land cover change and the deforestation challenge

  • 10,000 years ago: ~10.6 billion hectares of land; about 71% of Earth's land surface covered by forests, shrubs, and wild grasslands; ~29% deserts, glaciers, rocky terrain, and barren land.
  • Early landscape composition (approximate historical proportions):
    • 57% Forests; 6 billion hectares
    • 42% Wild grassland and shrubs; 4.6 billion hectares
  • 1700: ~55% Forests
  • 1900: ~48% Forests; 38% Wild grassland and shrubs; 31% Grazing? (context shows shifting land use)
  • 1950: Forest cover ~44%; 12% Crops; 15% Crops (some ambiguity in the slide); 1.6 billion ha under forests
  • 2023: ~38% Forests; ~30% Grazing land; ~3.2 billion hectares of agricultural land
  • Key takeaways:
    • Deforestation has been substantial over the millennia, with major declines in forest cover since 1900.
    • About 45% of land that was once forest/wild grassland/shrub is now used for agriculture.
    • Approximately 80% of agricultural land is used for livestock (grazing plus forage crops); roughly 20% is cropland used for human food and industrial uses.
  • Data sources cited include Williams (2003) for historical forests, HYDE for historical agriculture, and FAO for modern data; Our World in Data compiles the data (Licensed CC-BY).

Biodiversity and ecosystem services

  • Biodiversity (biological diversity): the variety of life in the world, in a particular habitat, or in a geographical location.
  • Why biodiversity matters:
    • Essential for ecosystem stability, resilience, and productivity.
    • Supports ecosystem services that benefit humans (food, feed, clean air and water, medicines, raw materials for construction, climate regulation, nutrient recycling, recreational values, etc.).
  • Examples of ecosystem services provided by biodiversity:
    • Food and feed resources
    • Medicinal and aromatic plants
    • Raw materials for building and construction
    • Climate regulation and nutrient cycling
    • Recreational and cultural values (e.g., national parks)

Course purpose, challenges, and goals (Introduction)

  • A fundamental challenge: increasing food production on less land due to deforestation and ecosystem limits.
  • The course aims to provide foundational knowledge on soils and how to manage them to enhance agricultural productivity.
  • Core message: Sustainable soil management is essential to meet future food demand without expanding agricultural land.

Section 1: Course structure and topics (Course overview)

  • Section 1 topics:
    • Soil properties: physical and chemical properties of soils
    • Biological properties of soil
    • Soil formation, morphology, and taxonomy
  • Section 2 topics (Soil and plants):
    • Soil, water, and plants
    • Soil and plant nutrition
    • Soil fertility management
    • Tillage and farming systems
  • Section 3 topics (Soil conservation and management):
    • Soil erosion and degradation
    • Soil pollution
    • Soil health
    • Soil policies and environmental laws
  • Acknowledgement: The course references include Beldin, S.I., and Perakis, S.S. (2009) and related USGS fact sheets, illustrating foundational soil science concepts and environmental considerations.

Connections and takeaways

  • Interdisciplinary view: Soil science integrates geoscience, civil engineering, ecology, and agriculture to address real-world problems (land use, infrastructure, ecosystem health, food security).
  • Sustainability focus: Balancing land use between agriculture, forestry, and biodiversity is essential to maintain ecosystem services and human well-being.
  • Quantitative literacy: Key ideas rely on quantitative measurements (e.g., HI, yields, land area distributions), so understanding and applying formulas is important, e.g.:
    • Harvest index: HI=Grain yieldTotal plant biomass\text{HI} = \frac{\text{Grain yield}}{\text{Total plant biomass}}
    • Interpreting trends in HI over time reflects breeding progress and management strategies.
  • Real-world relevance: Concepts link to global challenges such as feeding ten billion people, the role of the Green Revolution, and the need for sustainable soil management to support food production and environmental health.

Glossary of key concepts and formulas

  • Soil: The upper loose layer of the earth; context-dependent definition across disciplines.
  • Agroecosystem: A system consisting of crops, soil, livestock, and environment focused on agricultural production.
  • Hydrophonics: Growing plants in water.
  • Aeroponics: Growing plants with roots suspended in air, misted.
  • Harvest index (HI): HI=Grain yieldTotal plant biomass\text{HI} = \dfrac{\text{Grain yield}}{\text{Total plant biomass}}
  • Yield: Often expressed as tonnes per hectare (t/ha).
  • Land use terms:
    • Agricultural land, grazing land, arable land, urban land, forests, wild grassland.

References mentioned in the transcript (not exhaustive)

  • FAO and Our World in Data data on soils, land use, forest cover, and agricultural land.
  • Ray et al. (2017), Agrifood Atlas (yield and land use visuals).
  • Williams (2003) for historical forest data; HYDE for historical agriculture data.
  • Open references on biodiversity and ecosystem services (e.g., biodiversity collage imagery).