Soil Systems, Food Production, and Degradation Notes

5.1 Introduction to Soil Systems

• Soils are systems with inputs, outputs, storages, and flows.
• The soil system is illustrated by its soil profile, which has a layered structure.
• Soil Profile Layers:
  • O Horizon: Top layer, rich in nutrients, contains decayed organic material called humus, where significant growth occurs.
  • A Horizon: Mineral content mixes with nutrients.
  • Deeper Horizons (A, B, C, R): The ratio of organic matter to mineral content decreases with depth.
  • R Horizon: Predominantly bedrock, which determines the mineral content of the soil.
• Bulk of soil composition:
  • Abiotic Components: Mineral particles, air, and water.
  • Small proportion: Living organisms and decaying organic matter.
• Transfers within soils:
  • Biological Mixing: Organisms (earthworms, invertebrates, moles, rodents) churn and move materials without changing their state.
  • Leaching: Downward movement of minerals with water from the soil surface to deeper layers, potentially leading to nutrient loss for surface organisms.
• Inputs of organic material: Leaf litter, parent material (bedrock), precipitation, energy (sunlight, chemical energy from biomass).
• Outputs of matter: Uptake of water and nutrients by plant roots, soil erosion (loss of soil particles due to water or wind).
• Transformations in soil:
  • Decomposition: Breakdown of organic matter into simpler chemical compounds.
  • Weathering: Breakdown of parent rock into smaller particles (sand, silt, clay).
  • Nutrient Cycles: Nitrogen and carbon cycles.
    • Nitrogen Cycle: Bacteria (especially in leguminous plants) perform nitrogen fixation, converting atmospheric diatomic nitrogen $(N<em>2)$ into nitrates $(NO</em>3)$.
• Soil Quality and Productivity
  • Soil Particles: Sand, silt, and clay.
    • Sand: Largest particles, with large gaps, leading to good drainage and aeration.
    • Clay: Smallest particles, fitting tightly together, with little pore space, inhibiting drainage and retaining water.
    • Pore Space: Critical for water and air.
• Soil Texture Triangle:
  • A tool to determine the ratio of sand, silt, and clay in a soil sample.
  • Reading the Triangle: Similar to an x-y coordinate grid.
    • Sand: Bottom axis.
    • Clay: Left side (horizontal lines).
    • Silt: Right side.
• Soils as Ecosystems:
  • Contain both abiotic and biotic components.
  • Abiotic Components: Mineral content from parent bedrock, air, and water in pore spaces.
  • Biotic Components: Organisms (fungi, invertebrates, bacteria, rodents, rabbits, moles) contributing to biological mixing.
• Soil Structure and Properties:
  • Sand: Drains well, aerates well.
  • Clay: Inhibits drainage, holds water (can become waterlogged).
  • Silt: Blend of air and water space, retains water without excessive drainage.
  • Ideal Soil: Blend of sand, silt, and clay for drainage, water retention, and nutrient availability.

5.2 Terrestrial Food Production Systems

• Sustainability of food production systems depends on balancing social, economic, and environmental considerations.
• Consumers influence the system through food choices.
• Food Availability:
  • Varies globally due to differences in wealth, infrastructure, and government policies.
  • Uneven distribution leads to potential conflicts.
• Factors Influencing Sustainability:
  • Scale of farming operations, types of seeds and crops, water use, fertilizers, pest control methods, antibiotics in livestock, and government regulations.
  • Differences between MEDCs and LEDCs.
• Global Disparities in Food Production:
  • High-tech industrialized methods vs. traditional small-scale farming.
  • Disparities in resources, knowledge, and market access.
• Food Waste:
  • Patterns differ by region.
  • MEDCs: Waste at home or in restaurants.
  • LEDCs: Spoilage due to lack of proper storage and transportation.
• Influences on Food Choices:
  • Cultural traditions, economic situations, and political systems.
• Food System Connections:
  • Complex machine involving production, processing, packaging, and transportation.
  • Climate change, weather events, and economic policies affect the system.
• Arable Land Squeeze:
  • 1960: 0.42 hectares of arable land per person globally.
  • 2050 (projected): 0.14 hectares per person globally.
  • Driven by population growth, urbanization, and soil degradation.
• Land Use Efficiency:
  • Meat production uses 77% of global farmland but provides 17% of calories.
  • Plant-based foods use 23% of farmland but provide 83% of calories.
  • Eating lower on the food chain is more efficient.
• Cultural Influence of Meat Consumption:
  • Meat consumption as a sign of wealth or status.
  • Environmental impact: Higher land demand.
• Dietary Changes with Increased Wealth:
  • Increased consumption of meat and animal products.
  • Higher environmental footprint from beef.
• Farming Systems:
  • Diverse small-scale farming: Multiple crops, human labor, natural processes.
  • Large industrial agriculture: Monoculture, machines, chemicals, high yield.
• Sustainable Food System Strategies:
  • Reduce meat consumption.
  • Eat more plant-based foods.
  • Support local and organic foods.
• Food Labels:
  • Provide information on nutritional content, ingredients, and production methods.
  • Consumers can make informed choices to support sustainable systems.
• Oversight and Cooperation:
  • Government agencies and international organizations set and enforce standards.
  • Monitoring for soil health, water use, biodiversity, and fair label practices.
• Buffer Zones:
  • Natural vegetation around farmland captures excess nutrients and sediment.
• Crop Yields:
  • Vary globally and have changed over time.
  • Data helps understand global food security challenges.
• Farming Methods:
  • Commercial farming: Food for sale, monoculture, technology.
  • Subsistence farming: Enough food to feed a family.
  • Intensive: High labor and resources on a small area.
  • Extensive: Spreading out over large areas.
• Environmental Impacts of Terrestrial Food Production:
  • Soil erosion, water pollution, habitat loss, and climate change.
  • Severity depends on farming methods.
• Social and Cultural Connections:
  • Poor soil health leads to low crop yields, food insecurity, and poverty.
• Sustainable Agriculture Strategies:
  • Precision agriculture, integrated pest management, crop rotation, reducing food waste, and carbon storage in agricultural soils.

5.3 Soil Degradation and Conservation

• Fertile soils require significant time to develop through succession.
• Soils get deeper and more biologically complex over time.
• Soil horizons form over time, starting with bare rock.
  • Pioneer species (lichens) begin weathering.
  • Small annual plants, then perennial shrubs and grasses follow.
  • Soil becomes richer and deeper with each stage.
• Human activities may reduce soil fertility and increase soil erosion.
• Soil degradation results from changes in land use and management practices.
• Soil conservation strategies can preserve soil fertility and reduce erosion.
• Soil ecosystems change through succession.
  • Fertile soil contains a community of organisms that maintain nutrient cycles and resist erosion.
• Human Impacts:
  • Intensive grazing: Affects soil health due to animal diets, animal numbers, and soil compaction.
  • Urbanization: Expansion onto productive agricultural land reduces green space.
  • Over-irrigation: Leads to soil salinization.
  • Monoculture: Affects food supply for pests, biodiversity, and increases the need for herbicides and pesticides.
• Different Agricultural Approaches:
  • Commercial industrialized food production systems generally reduce soil fertility more than small-scale subsistence farming methods.
• Sustainable Practices:
  • Small-scale farming (e.g., in Kenya): Bean and banana intercropping demonstrates diverse crop selection and natural nutrient cycling.
• Soil Erosion:
  • Highland forests intercept and slow rainfall; roots absorb water and hold the soil.
  • Leaf litter adds organic matter to the soil, improving nutrient levels and fertility.
• Deforestation:
  • Replacing forests with agricultural fields disrupts the natural nutrient cycle.
  • Roots no longer hold soil in place, increasing erosion rates.
  • Nutrient levels decline.
• Agricultural Harvesting:
  • Thin layers of soil nutrients are lost when crops are removed from the land without proper nutrient replacement.
• Gully Formation:
  • Lack of roots to absorb water leads to increased runoff and topsoil loss.
  • Farmers cut more forest and plant on extreme slopes searching for fertile land, perpetuating soil loss.
• Soil Toxification:
  • Human activities (forest fires, volcanic activities, industrial effluence, agricultural chemicals) contribute to soil contamination.
• Salinization Process:
  • Flood or ditch irrigation leaves minerals behind as water evaporates.
  • Salts build up over time, exceeding plant tolerance and making the soil hostile.
• Soil Conservation Measures:
  • Soil Conditioners: Organic materials like compost improve soil health.
  • Enhance nutrient content, increase soil surface area, and improve water retention.
• Composting Operations:
  • Commercial facilities process large volumes mechanically.
  • Subsistence farmers create smaller, manually maintained compost piles.
• Wind Reduction Techniques:
  • Strategically placed windbreaks protect crops and soils.
  • Protected zone is eight to ten times wider than the height of the trees.
  • Reduces soil evaporation and creates beneficial microclimates.
• Cultivation Techniques:
  • Terracing transforms steep hillsides into productive agricultural land.
  • Slows wind and water movement, preventing erosion.
• Contour Plowing:
  • Plowing across hills instead of up and down creates mini-terraces.
  • Slows water movement and reduces erosion.
• Crop Rotation:
  • Different crops have different nutrient demands, maintaining soil fertility.
  • Legumes (beans, clover) replenish nutrients.
  • Disrupts pest cycles and reduces the need for pesticides.
• Companion Planting/Intercropping:
  • Optimizes nutrient use, minimizes pest problems, enhances biodiversity, and improves system resilience.
  • Different plants occupy different vertical spaces and root zones.
• Global Variations in Soil Degradation:
  • Differences between temperate and tropical zones, as well as between MEDCs and LEDCs.
• Key Relationships:
  • Soil ecosystem succession and fertility.
  • Ways human activities impact soils.
  • Range of management strategies available for commercial and subsistence farming systems.