1. BIOSPHERE Soils: Soil Profiles What is a soil? What does soil contain?
What factors affect soil formation?
Soil Profiles 1

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3. SOIL What is soil? INORGANIC MATERIAL ORGANIC MATERIAL AIR WATER
MINERALS FROM WEATHERED ROCKS
DEAD AND LIVING ORGANISMS
INORGANIC MATERIAL
ORGANIC MATERIAL
SOIL
AIR
WATER 3

4. WHAT ARE SOILS? INORGANIC MATERIAL = 45% OF SOIL VOLUME
WATER = 25% OF SOIL VOLUME
AIR = 25% OF SOIL VOLUME
ORGANIC MATERIAL = 5% OF SOIL VOLUME 4

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8. SOIL FORMATION AND SOIL PROFILES
A vertical section through the soil
From surface to the bedrock
Information comes from boring
the soil with an auger
Layers are called horizons 8

9. SOIL FORMATION AND SOIL PROFILES
Horizons can be used to work out the type of soil
There are usually four horizons in a model profile
O horizon – the surface, organic layer of decaying vegetation (where present)
LITTER – leaves, pine needles etc.
FERMENTATION LAYER – organic material begins to decompose here
HUMUS – decomposed remnants of plants and animals along with their waste products 9

10. SOIL FORMATION AND SOIL PROFILES
2. The A Horizon
Main top layer
Consists of organic and inorganic materials
Usually nutrient rich
Often referred to as topsoil
3. The B Horizon
Known as the subsoil
Coarser in texture: shows importance of weathering
Nutrients may be leached into the B horizon from the A
Leaching – removal of soluble minerals and humus downwards by rainwater 10

11. SOIL FORMATION AND SOIL PROFILES
4. The C Horizon
Zone of regolith
Large particles sit on top of underlying bedrock
Soil profiles vary in depth
Can be up to 50m
Average in the UK is 1.5m 11

12. SOIL FORMATION AND SOIL PROFILES
Depending on the variations within these variations it is
possible to group soils into a classification system
These zones include soils with certain common
characteristics. Closely linked with:
CLIMATE
VEGETATION 12

13. SOIL FORMING FACTORS
PARENT MATERIAL – the rock underneath, or other source material (e.g. from glacial, alluvial, volcanic deposition)
VEGETATION – e.g. Coniferous, Deciduous
LIVING ORGANISMS – worms and other creatures help to mix and improve the soil. Plants help stabilise soils and concentrate nutrients at surface of the soil
CLIMATE – Temperature and Rainfall
RELIEF – steepness of slopes, aspect of slope, height above sea level;
TIME – 100,000 YEARS!!!
NATURAL EVENTS – e.g. floods, glaciation, volcanic eruptions.
HUMAN ACTIVITY – farming, deforestation 13

14. WHAT ARE SOILS? Soil Formation and Soil Profiles section:
ACTIVITIES:
It is important to know the main factors which affect soil
Formation.
Use the Core Textbook to complete the following activities
in the:
Soil Formation and Soil Profiles section:
Questions 1 – 6 on page 174 14

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16. SOIL FORMATION STAGES IN SOIL FORMATION:
Weathering of parent rock over a considerable time period
Water, gas, living organisms and decaying organic matter added
Rate of weathering of parent rock depends greatly on climate (faster in hotter regions)
Where rainfall is heavier minerals are transported downwards in a process called leaching
Leached soils tend to be acidic
Type of vegetation in an area is linked to precipitation – this provides the humus area – more found in forest areas 16

17. (Weathered parent material)
TOPSOIL
SUBSOIL
REGOLITH
(Weathered parent material) 17

18. …and in more detail 18

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20. NEW TERMS
Eluviation
Downward movement of material where rainfall exceeds
evaporation
Illuviation
Accumulation of material in one layer of soil which have been
leached from a layer above
Leaching
Removal of soluble minerals and humus downwards by rainwater 20

21. Homework-Biosphere Textbook Questions
Homework due next Thursday (20th January)
Page 174
‘Soil Types, Case Studies and Catenas’
Questions 1 and 2 (all of)
Qu 2 a) use a whole jotter page for each soil profile.

22. BROWN EARTHS FOREST SOILS
                                                                                                                          
BROWN EARTHS FOREST SOILS
Brown earth is the soil that develops under deciduous forest.
It is found mainly on the west coasts of continents, in the cool temperate zones, 40° to 60° north and south of the equator.
These areas include north-western Europe (including the British Isles), the north-west of the United States, southern Chile, Tasmania, and South Island, New Zealand.
Brown earths have the second highest primary productivity of all soils, second only to tropical soils, the difference between them resulting from the winter season when deciduous trees are virtually dormant and the colder weather inhibits growth.
Brown earths are fertile and can develop to about 2 m (about 6 ft) in depth, because of the action of tree roots breaking up the parent rock.
If cleared, this soil can be productive for agriculture. 22

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25. BROWN EARTH SOILS EXPLANATION: Climate: DESCRIPTION:
Horizons less distinct
Mildly acidic due to a mull humus
A-Horizon is dark brown
B-Horizon is light brown
A-Horizon has a loamy texture
B-Horizon has a light texture
Generally free draining soil
EXPLANATION:
Climate:
Precipitation is greater than evaporation only in summer
Leads to moderate leaching
Warm summers 25

26. BROWN EARTH SOILS EXPLANATION: Vegetation and Soil Organisms:
Mixed broad leaf and much plant litter
Broken down easily by active soil biota and warmer climate
Greater abundance of earthworms, insects etc.
Quicker breakdown of material than podsol soil
Dark brown horizon as humus replaces material leached out
Leaching is less pronounced because evaporation and precipitation are more equally balanced
Colour lightens in the B horizon as humus becomes less abundant
Deep roots can penetrate the C horizon and extract minerals to ensure greater recycling 26

27. PODZOLS
Podzol soils are mainly found in the taiga (boreal forest) biome at latitudes greater than 60° in Eurasia and North America, and at higher altitudes in temperate latitudes.
They are also found in Britain in many moorland areas. Podzols form under a harsh, cold climate where growth is slow during the winter months and snow accumulates and stays on the ground for long periods.
The vegetation consists largely of coniferous trees, which are specially adapted to the climatic conditions, or moor and heathland plants in Britain.
Productivity is low due to the climatic conditions. The soils are impoverished and the climate is unsuitable for agriculture, but is suitable for commercial forestry.
Leaching is the key process at work in Podzols. 27

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30. PODSOL (PODZOL) SOILS DESCRIPTION: Horizons well defined Mor humus
Thin black layer with decaying litter needles
A Horizon very dark, then ash grey
B Horizon – red / dark brown
Iron pan can develop
A Horizon has a sandy texture
B Horizon has a denser texture (clayey)
Iron pan can impede drainage and cause waterlogging 30

31. PODSOL (PODZOL) SOILS EXPLANATION: Climate: Vegetation:
Colder climate – found at higher latitudes or altitudes
Lowers the rate at which litter is decomposed
Excess of precipitation over evaporation coupled with;
Spring snowmelt and rainfall contribute to leaching
Minerals are eluviated from the A horizon
This leads to colouring and iron-pan formation in the B horizon
Aluminium, iron and clay are re-deposited (illuviated)
Vegetation:
Coniferous vegetation – needles and cones
These are acidic in nature with a waxy coating
This leads to slow breakdown of organic matter
And an acidic humus layer 31

32. PODSOL (PODZOL) SOILS EXPLANATION: Biota:
Clearly defined horizons show a lack of soil biota
Lack of mixing of soil by earthworms
Reflects low winter temperatures 32

33. SOILS PAST PAPER QUESTION
For Brown Earth Forest Soil or a Podsol Soil:
Draw a soil profile and annotate it to show the main characteristics of the soil.
Explain the processes which have created this soil profile.
12 marks
Attempt b) 6 marks 33