Chapter 17 - Soils

Cyclone geography book, junior cert/ junior cycle

Soil - definition

Thin, uppermost layer of the earth

Uses of soil

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

Natural resource - definition

Essential natural resource

5 components of soil

Mineral particles, water, air, humus, organic matter

% of mineral particles in soil

45%

% of water in soil

25%

% of air in soil

25%

% humus in soil

4%

% organic matter in soil

1%

Function of mineral particles in soil

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

Types of mineral particles

sand (largest), silt, clay (smallest)

Mineral particles - definition

Broken down rocks

Permeability - definition

Ability of water to flow through

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

Function of air in soil

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

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

Organic matter - definition

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

Plant litter - definition

Leaves and twigs

How is humus made

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

Humus - definition

Dark, gel-like material that increases soil fertility

Function of humus in soil

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

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

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

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)

How does time affect soil formation

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

Soil profile - definition

Vertical section of soil from surface downwards

Horizon - definition

Soil’s layers

Characteristics of A horizon (topsoil)

1. Closest to surface

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

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

Characteristics of C horizon (bedrock)

Mixture of solid rock at base and smaller pieces at top

Impacts of soil formation

Leaching, breakdown of plant litter

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

Hard pan - definition

Thin crusty layer that is impermeable

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

Humification - definition

The process of plant litter changing into humus

Irish soil types

Brown, podzol, gley, peaty

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

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