Download Examine the processes that affect soil

Examine the processes that affect soil characteristics.
I am going to discuss this question under three different aspects - the processes of
humification, leaching and weathering and how they affect brown earth soils.
The first process I am going to discuss is humification. Humification is a vital
process in the formation of brown earth soils and affects the characteristics of humus
content, colour, ph, structure and water content. Humification in brown earth soils is
significantly influenced by the cool temperate oceanic found in northwestern Europe
and the native vegetation. The cool temperate climate provides up to 1500mm of rainfall
per year and mild temperatures ranging from 6-16 degrees celsius. This mild climate
allows humification to happen throughout the year as soil temperatures are rarely below
0 degrees.
The native vegetation in northwestern Europe is deciduous woodland. The
leaf-fall in the autumn and decaying trees provides plentiful organic matter, which is
converted into humus by micro-organisms. This results in a high humus content of
brown earths, which in turn makes them fertile soils for farming. Humus also has an
influence on soil colour, giving the brown earth their brown colour.
Humification also affects soil structure as the high humus content of brown earths
binds the soil particles together and this results in the crumb structure. The crumb
structure of the brown earths allows a higher water content as the water (and air) can
move in the pores between the soil peds (small lumps of soil made up of soil grains).
This means the brown earths can hold more water, which allows plants to soak up water
and dissolved nutrients.
Humification also affects the ph of the soil as the high humus content of brown
eaths prevents them being too acidic or alkaline. The neutral or near neutral ph of
brown earths means that it is much more suitable for micro-organisms and farming.
The relief in some areas also affect humification and this in turn affects soil
characteristics. Humification is slowed in high mountains, where temperature are colder
and where there is an absence of enough organic matter.
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Leaching is another major process in brown earth soils. The cool temperate climate
of northwestern Europe provides plentiful rainfall year round (between 800 - 1500mm
per year) and this results in the leaching of the humus content of the brown earth soils.
The leaching adds to the fertility of the soil by washing the nutrients down through and
around the soil, which makes it easier for plants to absorb the dissolved nutrients such
as iron, phosphorous and potassium.
Leaching also affects the soil colour as brown earths tend to have a light brown
colour due to the affect of leaching. The light brown colour is the same down through
the different horizons of the soil.
Leaching also affects the acidity of brown earth soils as the rainfall picks up
acidity from the humus and washes it through the soil. In some areas acidic brown
earth soils form because of the heavy rainfall leading to leaching by acidic rainwater.
Leaching can also affect the acidity of the soils through the effect of
chemical
weathering on the parent rock, which may produce slightly acidic brown earths, e.g.
sandstone in West Cork. These acidic brown earths often have a pale brown colour.
Leaching can also cause chemical weathering or rocks, e.g. hydrolysis of granite
produces clay particles, which are a component of brown earths.
In certain areas, where severe leaching occurs, brown earths may change into
gley soils as the soil becomes waterlogged and lacks oxygen.
Weathering is the third major process in brown earth soil formation. Weathering is
the break down of rocks into smaller components and happens in mechanical, chemical
and biological forms. Mechanical weathering is very important process for the formation
of brown earths. It is caused by freeze thaw action on rocks in upland areas, which
provides the soil grains that make up the soil as the scree falls to lowland areas. Soil
grains based on sandstone parent rock may provide slightly acidic soils and those
based on limestone provide slightly alkaline brown earths.Living organisms and plants
prefer slightly acidic or neutral soils, and for this reason brown earths contain a wide
variety of living things, whcih aids humification. These soils are the most productive
for farming. The parent rock can also influence the colour of brown earths, varying the
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colour from pale in the case of sandstone parent rock to darker brown in the case of
limestone.
Weathering provides the mineral content of the soils.Chemical weathering of
rocks releases important nutrients into the soils such as phosphorous, calcium and
iron. Calcium is released from limestone, clay particles from granite, sand particles from
sandstone and iron form iron oxide. As brown earths formed on various parent material,
it contains a good mix of nutrients.
As brown earths formed in the last 10000 years after the end of the last ice age,
brown earths are based on a variety of parent material and for this reason they have a
mixture of sand, silt and clay. The clay comes from the chemical weathering of granite
and deposition by melting glaciers, and the mechanical weathering of sandstone and
other rocks releases sand particles. The silt comes from river flood plains. This mixture
results in a loam texture, where the brown earth soil is crumbly to touch and has a
crumb structure. This structure allow water to pass between the soil peds (small lumps
of soil made up of soil grains) and thus prevents waterlogging. The water that passes
through brown earth soils allows plant absorption of nutrients, enables the survival of
the micro-organisms and and binds together the soil to prevent erosion.
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4 aspect marking scheme
3 aspect marking scheme
aspect heading = 4 marks
aspect heading = 4 marks
6 SRPs x 2 = 12 marks
8 SRPs x 2 = 16 marks
overall coherence = 4 marks
overall coherence = 7 or 6 marks
Aspect Total: 20 marks
Aspect Total: 27 or 26
Essay total: 4 x 20 marks = 80 marks
Essay total: 27 + 27 + 26 = 80 marks
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