Download File - leavingcertgeography

Study the diagram below.
Describe the influence of the various soil forming factors on the formation of
a Podzol soil.
Climate
Relief
Vegetation
SOIL FORMATION
Drainage
Parent Material
Soil Biota
• Cold, wet climates
• Coniferous Forests
• Thin: Weathering is slow
• Northern Latitudes
• Thin layer of humus:
Humification is slow
• Moorlands
• A lot of Leaching and
Podsolisation
• Iron and Aluminium
pushed down
•West of Ireland
• Needles don’t
decompose easily
little humification
• Produce an acid
humus
Relief
Vegetation
Climate
SOIL FORMATION
Drainage
• A Horizon often
waterlogged because
of impermeable iron
pan that forms
inbetween A and B
horizon.
Parent Material
• Weathered Slowly
producing a shallow
soil
Soil Biota
• Few Biota because
cold climate
• Therefore, little
humification
Brown Earths
2010 Question 18
Describe and explain the characteristics of any ONE soil
type studied by you
Mature soils have 3 distinct horizons (layers)
A Horizon – Contains topsoil, humus, vegetation not decayed, Organic
Content
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.
Brown Earths
• Where they are found
• Key words
• 40-60 Degrees in
Northern Hemisphere
• Zonal Soil
• Cool Temperate Climates
• Burrowers and Mixers
• Ireland-Russia in East
• Loamy
• Scotland-Portugal in
South
• Peds – space for water
• Most common soil in
Ireland
• Crumb Texture mostly
• Humification
• Boulder Clay from Ice age
deposits
• Freeze Thaw and Chemical
weathering
• Hydrolysis
Brown Earths
• Crumb Structure
• Micro-organism activity –
Bacteria
• Slightly acidic to slightly
alkaline – it varies 5-7
•
What impact do the
following process have
on Brown Earths ?
•
Weathering –
Mechanical/Chemical
•
Erosion
•
Leaching
•
Calcification
•
Humification
•
Salinisation???
Brown Earth Soil (10,000 years)
They form in warm climates, with mild winters
and summers. South East Ireland
Found in areas that have rainfall all year.
1,600-1,800 mm per year
Found in areas of deciduous forest – Oak/Ash
– Ireland's natural vegetation
Weathering is quite slow due to cool climate –
What types of weathering?
Some Humification because deciduous trees
shed leaves every year.
Mild climate assist decomposition
Lots of humus in these soils due to climate.
Some Leaching – because precipitation
exceeds evaporation.
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 washed down to here
(Eluviation)
• Horizons often Merge
•These are the main characteristics of the
Brown Earth Soil.Explain why these soils
have these characteristics eg. Quite
shallow because of slow weathering.
Which is due to the cool climate etc.
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
soil
Brown earth soils are widespread in Ireland, except in highland areas. Soil organisms, like earthworms, mix the
materials together, merging the boundaries between the horizons. These soils are leached, but not heavily, so
the aluminium and iron oxides are dispersed through the soil to give the overall brown colour. The original
vegetation was deciduous forest, resulting in a layer of decaying leaves giving a rich humus. The deep roots
of these trees reached down to the 'B' horizon (unlike coniferous trees) tapping the nutrient supply and
allowing good drainage.
Climate -Precipitation greater than evaporation during summer months, resulting in only moderate
leaching. Warm summers
Natural vegetations and soil organisms - mixed broad leaf, much plant litter through this is more easily broken
down by more active soil biota. A moderate or moder type of humus would develop from the plant litter
Relief and drainage - downward movement of water, moderate leaching likely
Parent material - strong influence on soil development
They generally have three horizons: the A, B and C horizon. Horizon A is usually a brownish colour, and over
20 cm in depth. It is composed of mull humus (well decomposed alkaline organic matter) and mineral matter. It
is biologically active with many soil organisms and plant roots mixing the mull humus with mineral particles.
As a result, the boundary between the A and B horizons can be ill defined in unploughed examples. Horizon B is
mostly composed of mineral matter which has been weathered from the parent material, but it often contains
inclusions of more organic material carried in by organisms, especially earthworms. It is lighter in colour than
the A horizon, and is often weakly illuviated (leached). Due to limited leaching only the more soluble bases are
moved down through the profile. Horizon C is made up of the parent material, which is generally permeable and
non- or slightly acidic, for example clay loam.
Brown Earths - Characteristics
Colour
Texture
Structure
Humus Content
Water Content
PH Value
Brown Earths - Colour
•
Brown due to soil formation processes
•
Humification is main process – Dark Brown
•
What is humification?
•
What Plant Litter creates the humus?
•
How does humus make its way down through the soil?
•
No Distinct Horizons
•
Burrowers/Mixers – impact of climate
Brown Earths - Texture
•
How fine or coarse the soil is
•
Equal amts of Sand and Silt and Clay = Loamy
•
Loamy means space for air and water to pass through
•
Well Drained
•
Crumby structure due to rich organic content of soil and
living organisms
•
Mild temperatures – Cool Temperate Oceanic
•
This helps – Burrowers and Mixers
Brown Earths – Humus Content
•
Rich due to Deciduous Vegetation
•
Process = Humification
•
Moderate rainfall – eg. 1600-1800 mm in South East
of Ireland
•
Relief also affects the humus content – too high =
less. The humus content in South East is affected by
low-lying,undulating land
•
Mild Winters/Warm Summers – Decomposition is
highest in these conditions
BROWN EARTHS – PH Value
•
Refers to how acidic or alkaline the soil is
•
Acidic soils = low ph value
•
Alkaline soils = high ph value
•
Parent Rock generally influences the ph value
•
Acidic Brown Earths form on Sandstone and Alkaline
Brown Earths form on Limestone
•
PH Values of Brown Earths encourage the activity of
earthworms and Bacteria