Learning Objectives

Understand soil formation

Success Criteria

• Describe soil formation

• Describe the layers of a soil profile

1

What is soil.....Soil is a mixture of particles of weathered rock,

decayed organic matter, water and gases in

which living organisms are present.

•Soil is a very delicate, fragile living thing•Soil is a previous resource•Pedology is the study of soil•Pedologistists are soil scientists•Soil is made up of 4 main components

BBC - Learning Zone Class Clips - What is soil? - Science Video

4 components of soil

Soil Profiles.....•As a result of various inputs/ outputs, soils

tend to develop a series of distinct layers

(Horizons)

•These layers are identifiable by variations in

colour and texturetexture but are also different in

their mineral content and organic matter.

Soil Profiles L = leaf litter – may consist of leaves, pine needles, cones and grass

F = Fermentation layer – where organic matter starts to decompose

H = Humus – decomposed remains of vegetation, animals and bacteria

A horizon (topsoil) mixture of mineral matter and organic matter.

LFH

A

B

C

D

Soil Profiles

B horizon (subsoil) – coarser texture and contains more mineral matter from weathered parent material. Less organic matter

C horizon – zone of REGOLITH (weathered parent material)

LFH

A

B

C

D

Learning Objectives

Understand soil formation

Success Criteria

• Explain the factors affecting soil formation

2

Factors affecting soil formationCROPT

•Climate

•Relief

•Organisms

•Parent Material

•Time

Climate

•Warm temperatures mean a fast decomposition

•Cold temperatures mean a slow decomposition

• If precipitation exceeds evaporation then leaching will occur vertically and down slope

• If evaporation exceeds precipitation then minerals and water can be drawn up through the soil. This is called capillary movement.

Relief•Influences soil depth and drainage

•Altitude means temperatures decrease and precipitation increases

•North facing slopes are colder and wetter than south facing slopes.

Very thin soils

Deeper, thick soils

Organic Matter•This is the actions of organisms and vegetation, biotic

factors and organic soil.

•There is a wide range and they all interact with each other.

•They are also influenced with climate too

•They help to form humus.

Mor Humus

Associated with

cooler, wet climates.

Worms are NOT

common so there is

limited mixing of

organic and mineral

material

Mull Humus

Develops beneath

deciduous woodland

whose leaves are rich

in minerals. There is

no clearly defined

humus layer, unlike

the mor.

Geology (parent material)

•Parent material influences,

▫Rate of weathering (hard rocks = thin soils)

▫Chemical composition/ soil colour

▫Soil texture

Time

Soils change over time

as a result of the

addition of organic

matter and the activity

of organisms.

It may take 100 years to

form 1cm of soil.

Recent soil

Buried soil

Learning Objectives

Understand soil formation

Success Criteria

• Describe the location of 3 soils

• Draw and annotate 3 soil profiles

3

The 3 types of soil you need to be aware of are:

Three types of soil

• Gleys

• Podzols

• Brown Earths

Learning Objectives

Understand soil formation

Success Criteria

• Describe and explain the formation of a

Podsol soils

4

Podzol

Podzol - from the Russian words;

pod = under

zola = ash

Podzols in Scotland

Describe and Explain the profile • Podsols usually have clearly defined horizons due to a

process called podsolation. This involved pronounced leaching of material from surface layers to lower layers.

• Found in cold climate where precipitation exceeds evaporation.

• Podsols are also found in upland and moorland areas where soils are thin.

• The Ao horizon forms from decaying plant matter (pine needles, cones, twigs, dead heather) decomposes slowly due to cold climates to form a mor humus.

• Rain and melting snow combine to wash out (elevate) minerals from A. This produces an ash coloured, bleaches horizon.

• Lower down the profile. Aluminium, iron, clay and humus are washed in (illuvated) and re-deposited in the subsoil/ B.

• The presence of iron explains the reddish brown colour.

• If the iron accumulates over a long period pf time a rust coloured iron pan can form. This can prevent the penetration of roots, the drainage of the soil and can result in water logging.

• The cold climate also hinders biotic mixing eg; worms, of the soil again explaining clearly defined horizons.

• C horizon forma s a range of parent material or could be serived from acidic rocks – perhaps even a glacial till.

Podzol: Soil forming factors

• Time • Since end of last ice age 10,000 years

• Topography • Stable sites from sea level to mountain summits

• Climate • Cool• Precipitation greater than

evaporation

• Vegetation/ organisms

• Coniferous woodland/heather moorland

• Slow breakdown, limited or no mixing

• Acid rocks, often from granite or schist

• Parent material

Uses of Podzols•Generally infertile, non-productive

•Forestry and recreation (e.g. forestry plantations, grouse moors). In Scotland used for grass production and stock rearing

•Associated with coniferous forests

•When used for agriculture the top soil is often limed (to decrease acidity) and artificially fertilised (to increase nutrient status)

Learning Objectives

Understand soil formation

Success Criteria

• Describe and explain the formation of a

Brown Earth soils

5

Core Higher Textbook

•Using page 166 of textbook, draw and annotate the Brown-Earth soil profile.

Brown Earth Soil

Describe and Explain the profile

•Brown earth soils develop beneath temperate deciduous forests. They are found in Europe, Russia and N. America.

•The Ao horizon is rich in nutrients thanks to thick leaf litter from the deciduous trees.

•This litter decomposes quickly due to milder climate resulting in a less acidic mull humus.

•Soil is well mixed thanks to earthworms and soil bacteria. This means that it is well aerated and has a loamy texture.

•The topsoil is dark brown in colour because the thick humus from the Ao replaces minerals that have been leaches out. Leaching is less pronounced because of a closer balance between evaporation and precipitation.

•The B horizon is lighter in colour and there is less humus.

•The C horizon is penetrated by tree roots which mix the soil resulting in no clearly defined horizons.

Brown Earth: Soil forming factors

• Relatively warm, dry• Climate

• Generally low lying areas• Topography

• Vegetation/organisms • Broadleaf woodland, mull humus, indistinct horizons

• Rapid decomposition

• Often earthworms and other mixers

• Variable soil texture

• Parent material

• Relatively young - Since end of last ice age c10,000 years

• Time

Uses of Brown Earths•Amongst the most fertile soils in Scotland

•Agriculture e.g. winter vegetables

•Fertilisers required to maintain nutrient levels

•Occurring on gently undulating terrain

•Sheltered sites suit growth of trees

Test yourself: Brown Earths

Write down 3 characteristics of a

brown earth

Draw a sketch profile of a brown

earth labelling the different

horizons with the correct letters

Learning Objectives

Understand soil formation

Success Criteria

• Describe and explain the formation of

tundra gley soils

6

Gley

Gley-from the Russian word; glei= compact bluish grey

Describe and Explain the profile• Topsoil and subsoil can become frozen in winter.

• As the soil thaws in summer the topsoil drains into the subsoil (which is still frozen) and the soil becomes waterlogged.

• When soil is waterlogged for a long time its pore spaces lose oxygen. This is called anaerobic and means that the decay of bacteria is slowed down.

• Iron compounds in the soil are reduced chemically from their normal red brown to a grey blue colour. Seasonally due to drying out this process is reversed.

• Due to seasonal change there is a mottled appearance with orange- brown mottles set in the blue grey subsoil (indicating the return of oxygen to the soil).

• Due to the freezing the profile is badly drained and has clear horizons. Biotic mixing does not occur as organisms cannot cope with the cold climate, nor penetrate the permafrost.

• Organic matter at the Ao accumulates as debris from shrubs, rushes and grasses fall. This decomposes very slowly due to a lack of bacterial activity becoming an acidic mor humus.

• The C horizon is often clay and this impermeable layer contributed to the poor drainage of the soil type.

Gley profile

Orange/yellow mottles

Gley: Soil forming factors

• Since end of last ice age 10,000 years ago

• Time

• Where groundwater high/ impermeable layer below

• Topography

• High rainfall/ precipitation• Waterlogging

• Climate

• Lichens, mosses, marshy vegetation

• Vegetation/organisms

• Parent material • Variable - coastal sand to glacial till

Uses of Gleys

• Peat for fuel

• Due to water-logging they have limited

agricultural use. Can be used for sheep grazing.

• They support wet plant species and are used for

rough grazing and forestry

Soil Catenas•Although soils form across broad climatic areas,

there can be widespread variations on a local level.

•A soil catena is a sequence of different soil profiles

that develop down a slope.

•Podzols are found in the colder climates near to the

top of the hill, brown earths on more freely

drained land further down and waterlogged gleys to

the valley bottom.

Peat

Soil Catenas

Podzol with iron pan

Brown Earth

Gley (unless drained)

Past paper Q - 2009

Draw and fully annotate a soil profile of a

brown earth to show its main characteristics

(including horizons, colour, texture and

drainage) and associated vegetation.

Past paper Q – 2009 – How to answer

• State the associated vegetation – big/ small roots?

• Describe and explain the full profile starting with the

L/F/H horizons. (Ao)

• A horizon – Colour, texture e.g. Ash-grey upper A

horizon with sandy texture.

▫Zone of eluviation – what does it mean?

• B horizon – impact of iron pan

▫Zone of illuviation

• Explicitly state changes in colour and texture

Past paper Q – 2009 – How to answer

• E.g. B horizon is reddish-brown with denser texture.

• Precipitation exceeds evaporation, giving downward

leaching.

• C horizon – discuss parent material - generally

weathered rock or glacial or fluvio-glacial material.

• ALWAYS refer back to the question .

What do you remember....?

Describe and explain the

characteristics of a brown earth soil

including horizons, colour, texture

and drainage.

10 marks