Geography - Chapter 14 Soils

The composition of soil

• Mineral matter

• Humus

• Air

• living organisms

mineral matter

• 45% of soil

• Largest component of soil

• Comes from broken down bedrock

• stones, sand, clay and silt

• Helps nourish plants

Humus

• 4% of soil

• Dark, jelly like substance

• Rich in nutrients

• forms when dead plants and leaves decay on top of the soil

• process called ‘humification’

• Living organisms mix material through soil

• Helps bind soil together

• increases fertility

Air

• 25% of soil

• Found in space between soil particles

• supplies oxygen and nitrogen

• enables living organisms to live in soil

Water

• 25% of soil

• Important, helps plants grow

• dissolves nutrients and minerals

Living organisms

• 1% of soil

• Earthworms and insects

• burrow through soil, allowing water/air to pass

• helps to mix the soil

• bacteria and fungi also live here

• help form humus

Soil profile

• Cross section down through a soil

• Shows the layers that make up the soil

• These layers are called horizons

O horizon

• The soil surface we see

• Leaves, branches that decompose to form humus

A horizon

• Topsoil

• has highest humus content

• this layer contains the most living organisms

B horizon

• Subsoil

• lighter in colour

• contains less humus

• partially made up of rocks

C horizon

• Bedrock

• Consists of rock particles and solid bedrock

Types of soil

Brown soil

• Ireland’s most common type of soil

• dark brown

• areas once covered in deciduous trees

• Midlands, south, east Ireland

• humification

• rich humus moderate rainfall supply soil with nutrients

• Fertile, well-drained soil

• good for arable or pastoral farming

Podzol

• Grey

• Coniferous forests

• cold, wet, upland areas

• Wexford, Cork and Galway (West of Ireland)

• Excessive rainfall-leaching

• Leaching= the washing of nutrients down through the soil horizons

• Impermeable layer- leaching

• Impermeable= Water can not pass through it

• Hardpan

• Infertile and slightly acidic

Peat soils

• Black

• Limited plant litter available (deciduous)

• mountain locations in the midlands

• high levels of rainfall lead to waterlogging

• leaching occurs

• infertile soil

Gley

• Blue-grey

• impermeable bedrock or high percentage of clay

• Ulster, north midlands, Clare, Limerick

• Waterlogging occurs

• Infertile soil

Exploitation of soil

Natural resource

A material in nature that we can utilize to improve life quality

Soils

• foundation and nutrients for plant growth

• Filter and store water we drink

• protecting soil helps stop climate change

• Provides antibiotics

Overgrazing

• When too many animals graze in a limited space and remove the plant cover from soil.

• exposes soil to wind and rain, which can remove topsoil

• cause erosion

How soil is formed

Bedrock

• Broken down by weathering

• some rocks weather slowly (Impermeable) Granite

• Others quickly (permeable) limestone

• The type of rock effects the characteristics of the soil

Relief

• highland areas are more wet, so there is more water in the soil

• can lead to leaching or soil becoming waterlogged

• less humus

Climate

• Rainfall and temperature determine the rate at which the rock is broken down by weathering and erosion

• freeze thaw action slowly breaks down rocks in colder areas

• results in thin soil

• wet areas leaching occurs

• soils are then infertile

• in dry areas soils are so dry water can’t get in