Soils: Tropical Latosols: To be studied as part of Otional Unit 7 - Geoecology - for the Leaving Cert Geography Examination.

1. Tropical Latosols
Latosol – A Tropical Rainforest Soil

2. You may be asked the following:
“Compare and contrast the characteristics of any
two soil types which you have studied.”
That is why you must know Irish Brown Earth Soils and
Latosols (tropical rainforest soil).
Exam Brief

3. • Typical Exam Questions:
• Describe and explain the characteristics of any one soil type
studied by you.
• With reference to one soil type studied by you, examine
how parent material, climate and organic matter influence
the soil.
• Examine the general composition of any one soil type that
you have studied.
Exam Brief

4. • Zonal soil type: developed in response to tropical and
equatorial climates that are hot (average 27C), humid (88%
humidity) and wet (up to 6,000mm per annum).
• Latosols:
•
•
•
•
•
Red, heavily leached infertile zonal soils.
Occupy 7.5% of total land area.
Cover large areas of South America, Africa and Asia.
Major obstacle to development of profitable agriculture.
Fragile soils which can be easily damaged creating a useless
laterite.
Soil Type: Zonal

5. • Latosols:
• Support the richest vegetation on the planet – the tropical
rainforests. But how if latosols are not fertile?
• The relationship between soil, climate and vegetation in
tropical regions causes a short nutrient cycle. Plants
grow rapidly, otherwise they will not get the nutrients
before they are leached by the high rainfall.
• If vegetation is removed the soils quickly become
infertile and vulnerable to erosion.
Soil Type: Zonal

6. O
Horizon
• Thin O Horizon (humus layer) due to intense bacterial activity which
rapidly decomposes dead organic matter.
• Contains aluminium and iron oxides.
• Sometimes iron and aluminium compounds build up in a hard layer
A
Horizon down the profile.
B
Horizon
C
Horizon
• Very deep.
• Uniform in texture due to intense leaching in high temperatures.
• Consists of parent rock.
Soil Profile of a Latosol

7. 1.
2.
3.
4.
5.
Climate
Relief
Parent material
Living Organisms
Time
Factors affecting latosols

8. 1. Climate:
• Latosols form in very hot, wet conditions in the tropics
and equatorial regions. High rainfall, humidity and
temperatures cause deep chemical weathering and rapid
leaching of minerals down through the soil.
• Average rainfall: 3,000mm.
• Humidity: High – 88%
• Average temperature: 27°C
• Latosol soils are very deep – high temperatures and
permeability of soil mean heat and moisture reach great
depths and rot the parent material into a deep soil.
Factors affecting latosols

9. 2. Relief
• Latosols form under the rainforest on flat land and
on slopes which allow tree growth:
• Thicker on flat land.
• Thinner and better drained where land is sloping.
Factors affecting latosols

10. 3. Parent Material
• Parent materials found under latosols in
Brazil vary from metamorphic to
sedimentary rocks.
• These different parent materials cause the
latosol to vary in colour from red to yellow.
Factors affecting latosols

11. 4. Living Organisms
• Hot and damp conditions of the forest floor are
perfect for fungi and bacteria to thrive and cause
rapid humification. This provides plentiful
nutrients but these nutrients are in high demand so
they do not remain in the soil for long.
• This nutrient cycle in latosols is very short – a few
days in some cases.
Factors affecting latosols

12. 5. Time
• Deep latosols result from the rapid weathering of
parent material and the fast breakdown of organic
material by fungi, bacteria and other living things.
• Tropical regions were not affected by the last ice
age and so have had many thousands of years to
develop.
Factors affecting latosols

13. Colour
• Red or yellow – due to
aluminium and iron
compounds left over
from leaching.
Characteristics of Latosols

14. pH
• Moderately acidic.
• Rapid absorption of
nutrients by vegetation
growing in soil prevents
latosol becoming more
acidic.
• Once forest is cleared,
latosol acidity rises.
Characteristics of Latosols

15. Humus Content
• Low humus content.
• Rapid breakdown of organic material
but equally rapid uptake of humus by
plants.
• Any humus formed is quickly absorbed
by plants.
Characteristics of latosols

16. Structure
• Latosols lack a clearly defined structure.
• Structure is often poorly developed
due to intense chemical weathering of
mineral grains which prevents well
shaped peds forming.
• Where parent rock is
granite, chemical weathering causes
clay minerals to form giving the latosols
a platy structure.
Characteristics of latosols

17. Texture
• May be any texture – loamy / clay /
sandy.
• This is due to a variety of parent
material.
• Latosols formed on metamorphic or
igneous rock tend to have a more
sandy texture.
Characteristics of latosols

18. Water content
• Wet due to high rainfall in tropical
region.
• Latosols are very permeable
(water passes through easily).
• But, if forest cover is removed,
the soil dries out rapidly and
becomes impermeable.
Characteristics of latosols

19. 1. Laterisation
2. Humification
Processes Affecting
Latosol Formation

20. 1. Laterisation
• Definition: A combination of deep leaching and
chemical weathering by carbonation, oxidation and
hydrolysis.
• Dominant process in forming latosols.
• Leaching and chemical weathering in the high
temperatures of the tropics combine to dissolve all
minerals except iron and aluminium oxides. These
minerals give the soil its distinctive red colour.
• Due to the constant high temperatures, these soilforming processes have reached deep ground and
formed soils up to 40m deep.
Processes Affecting Latosol Formation

21. 2. Humificaiton
• Hot, damp conditions = rapid humification.
• This provides plentiful nutrients easily absorbed by
plant roots.
• These nutrients stay close to the surface of the soil
because they are quickly absorbed by the plants of
the rainforest.
Processes Affecting Latosol Formation