Chapter 17 - Soils

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Cyclone geography book, junior cert/ junior cycle

Geography

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37 Terms

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Soil - definition

Thin, uppermost layer of the earth

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Uses of soil

Grows plants as food source, building, farming, pottery, antibiotics

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Natural resource - definition

Essential natural resource

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5 components of soil

Mineral particles, water, air, humus, organic matter

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% of mineral particles in soil

45%

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% of water in soil

25%

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% of air in soil

25%

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% humus in soil

4%

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% organic matter in soil

1%

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Function of mineral particles in soil

Smaller particles pack closely and slow down flow of water. Composition affects permeability

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Types of mineral particles

sand (largest), silt, clay (smallest)

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Mineral particles - definition

Broken down rocks

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Permeability - definition

Ability of water to flow through

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Function of water in soil

  1. Binds soil together.

  2. Dissolves minerals and nutrients in soil so plants soak them up in liquid form through roots

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Function of air in soil

  1. Found in pores (spaces) between soil particles.

  2. Provides oxygen and nitrogen for plants, oxygen for organisms

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Organic matter - definition

Anything living found in the soil, e.g. earthworms, micro-organisms (bacteria)

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Plant litter - definition

Leaves and twigs

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How is humus made

Plant litter decays in soil. Also formed by dead animals.

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Humus - definition

Dark, gel-like material that increases soil fertility

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Function of humus in soil

Fertilizes soil. Darker the soil, more humus it has and more fertile it is

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Functions of worms in soil

  1. Worms move through to help air and water circulate.

  2. Aid in formation of humus by eating plant litter and dead animals and excreting it, fertilizing soil

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How does climate impact soil formation

  1. Provides water through precipitation

  2. Provides frost, water, weather to erode rock that forms mineral particles

  3. Influences vegetation and living organisms. Vegetation leaves plant litter, organisms change to humus

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How does human activity affect soil formation

  1. Fertilizer improves soil, e.g. compost

  2. Overuse damages soil, e.g. monoculture (cultivation of single crop in given area)

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How does time affect soil formation

Takes long time to form (sometimes hundreds of year per cm depth)

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Soil profile - definition

Vertical section of soil from surface downwards

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Horizon - definition

Soil’s layers

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Characteristics of A horizon (topsoil)

  1. Closest to surface

  2. Dark in colour and fertile because most humus and plant litter

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Characteristics of B horizon (subsoil)

  1. Found below topsoil

  2. Lighter in colour because less humus

  3. More stones then top soil because closer to bedrock

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Characteristics of C horizon (bedrock)

Mixture of solid rock at base and smaller pieces at top

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Impacts of soil formation

Leaching, breakdown of plant litter

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Why is leaching bad for soil

  1. Deprives plants of important nutrients and minerals when washed out of reach of roots in B horizon

  2. Creates hardpan when iron oxide minerals washes from top soil particles. Collects at bottom of topsoil just above subsoil. Causes top soil to become flooded and waterlogged

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Hard pan - definition

Thin crusty layer that is impermeable

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How does breakdown of plant litter impact soil formation

  1. Plant litter broken down by insects and microorganisms to humus

  2. Oxygen also needed to keep organisms alive

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Humification - definition

The process of plant litter changing into humus

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Irish soil types

Brown, podzol, gley, peaty

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<p>Formation of brown soil</p>

Formation of brown soil

  1. Most common soil type in Ireland

  2. Brown in colour because humus

  3. Found in areas with not a lot of rainfall

  4. Found in areas of deciduous forest because of plant litter

  5. Good for farming

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Formation of podzol soil

  1. Found in upland areas with more rainfall

  2. Grey in colour due to hardpan caused by leaching

  3. Used for forestry as not great for farming (coniferous trees)

  4. Not fertile because no plant litter from coniferous trees