Syllabus concepts to know

• 5.1.1 Soil is a dynamic system within the larger ecosystem that has its own inputs, outputs, storages and flows.
• 5.1.2 Soil is made up of inorganic and organic components, water and air.
• 5.1.3 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.
• 5.1.4 Soil system inputs include those from dead organic matter and inorganic minerals.
• 5.1.5 Soil system outputs include losses of dead organic matter due to decomposition, losses of mineral components and loss of energy due to heat loss.
• 5.1.6 Transfers occur across soil horizons, into and out of soils.
• 5.1.7 Transformations within soils can change the components or the whole soil system.
• 5.1.8 Systems flow diagrams show flows into, out of and within the soil ecosystem.
• 5.1.9 Soils provide the foundation of terrestrial ecosystems as a medium for plant growth (a seed bank, a store of water and almost all essential plant nutrients).
• 5.1.10 Soils contribute to biodiversity by providing a habitat and a niche for many species.
• 5.1.11 Soils have an important role in the recycling of elements as a part of biogeochemical cycles.
• 5.1.12 Soil texture defines the physical make-up of the mineral soil.
• 5.1.13 Soil texture affects primary productivity through the differing influences of sand, silt, clay and dead organic matter, including humus.
• 5.1.14 Soils can act as carbon sinks, stores or sources, depending on the relative rates of input of dead organic matter and decomposition.
• 5.1.15 Soils are classified and mapped by appearance of the whole soil profile.
• 5.1.16 Horizons are horizontal strata that are distinctive to the soil type.
• 5.1.17 The A horizon is the layer of soil just beneath the uppermost organic humus layer, where present.
• 5.1.18 Factors that influence soil formation include climate, organisms, geomorphology (landscape), geology (parent material) and time.
• 5.1.19 Differences between soils rich in sand, silt or clay include particle size and chemical properties.
• 5.1.20 Soil properties can be determined from analysing the sand, silt and clay percentages, percentage organic matter, percentage water, infiltration, bulk density, colour and pH.
• 5.1.21 Carbon is released from soils as methane or carbon dioxide.