2.soil formation By Allah Dad Khan

2. • Soil formation By Allah Dad Khan

12. SOIL FORMATION
Climate Relief Vegetation
Drainage Parent Material Soil Biota
Study the diagram below.
Describe the influence of the various soil forming factors on the formation of
a Podsol soil.
10 Marks

13. SOIL FORMATION
Climate
Relief Vegetation
Drainage Parent Material Soil Biota
• Cold, wet climates
• Thin: Weathering is slow
• Thin layer of humus:
Humification is slow
• A lot of Leaching and
Podsolisation
• Iron and Aluminium
pushed down
• Northern Latitudes
• Moorland
• Coniferous Forests
• Needles don’t
decompose easily
little humification
• Produce an acid
humus
• A Horizon often
waterlogged because
of impermeable iron
pan that forms
inbetween A and B
horizon.
• Weathered Slowly
producing a shallow
soil
• Few Biota because
cold climate
• Therefore, little
humification

14. Mature soils have 3 distinct horizons (layers)
A Horizon – Contains topsoil, humus, vegetation not decayed, biota
The most fertile part of the soil
Suffers the most leaching
B Horizon - Contains subsoil
Contains leached mineral from A horizon
C Horizon - The Regolith (recently formed soil)
Sits ontop of bedrock
Contains large particles.

15. Brown Earth Soils
They form in warm climates, with mild winters
and summers.
Found in areas that have rainfall all year.
Found in areas of deciduous forest
Weathering is quite slow due to cool climate
Some Humification because deciduous trees
shed leaves every year.
Mild climate assist decomposition
Lots of biota in these soils due to climate.
Some Leaching – because precipitation
exceeds evaporation.

16. What does it look like?
• Quite shallow
• Quite thick Humus
• Mild Acid Humus
• Light Brown A Horizon – because
calcium,
magnese
are leached out by rain
• Dark Brown B Horizon – because
minerals have been
illuviated here.
• Horizons often Merge
These are the main characteristics of the
Brown Earth Soil.
Explain why these soils have these
characteristics eg. Quite shallow because

17. What does it look like?
• Quite shallow - weathering is slow
• Quite thick Humus – because there is
some humification
• Mild Acid Humus – because
humification is slow
• Light Brown A Horizon – because
calcium,
magnese
are leached out by rain
• Dark Brown B Horizon – because
minerals have been
illuviated here.
• Horizons often Merge - biota mix the