5.1 Soil

• Own inputs, outputs, storages, flows within larger ecosystem

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• Inorganic and organic components, water, air

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• Soils develop a stable, layered structure known as a profile made up of several horizons, produced by interactions within the system over long periods of time • Soil profiles have distinctive horizons that show a transition from more organic components in the upper surface to inorganic below • 2.5 Application of skills • Sample two soils from the subsoil (B horizon): one from a local garden or field, and one from a natural ecosystem

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• Soil system inputs include those from dead organic matter and inorganic minerals • Dead organic matter inputs may include, but not be limited to, plant litter, dead animal biomass, manure • Organic mineral inputs may include weathering, deposition or decomposition, precipitation (water with dissolved minerals), gases, air, humidity and solar energy • In managed soil systems, many inputs are anthropogenic: compost, fertilizer, agrochemicals, irrigation, salinization

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• Soil system outputs include losses of dead organic matter due to decomposition, losses of mineral components and loss of energy due to heat loss • Mineral component outputs include wind or water erosion, water and mineral absorption by plant roots, leaching of dissolved plant nutrients and water, diffusion of gases • These outputs can cause the loss or modification of soil components and are different from total loss of soil by erosion; however

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• Transfers occur across soil horizons, into and out of soils • Include: infiltration, percolation, groundwater flow, biological mixing, aeration, erosion and leaching

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• Transformations within soils can change the components or the whole soil system • Include: decomposition, weathering, nutrient cycling and salinization

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• Systems flow diagrams show flows into, out of and within the soil ecosystem • Soil systems are essential for the water, carbon and nitrogen cycles

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• Medium for plant growth (seed bank, water store, nutrients) • Stores nitrogen, phosphorus, potassium • Carbon obtained from atmosphere

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• Provides habitat and niche for many species • Microorganisms, animals, fungi

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• Role in biogeochemical cycles • Detritivores (earthworms) and saprotrophs (fungi, bacteria) decompose matter

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• Physical make-up of mineral soil • Proportions of sand, silt, clay, humus

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• Influences nutrient retention, water retention, drainage, aeration

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• Can act as sinks, stores, or sources • Depends on input rate vs. decomposition rate

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• By appearance of whole soil profile • Profile diagrams show transfer/transformation processes

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• O: organic layer • A: mixed layer (topsoil) • B: mineral soil • C: parent rock

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• Rich in organic matter • Most valuable for plant growth • Most vulnerable to erosion and degradation

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• Climate, organisms, geomorphology (landscape) • Geology (parent material), time

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• Particle size and chemical properties • Sand/silt: low cation-exchange capacity (CEC) • Clay: high CEC (increases mineral availability)

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• Sand/silt/clay percentages, organic matter, water • Infiltration, bulk density, colour, pH

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• Released as methane or CO₂ • Causes: global warming, agriculture, wetland drainage • May lead to tipping point

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