Composition and Characteristics of one Soil Type

Examine the general composition and characteristics of any one soil type (80 Marks)

Zonal soils and intrazonal soils

Brown Earth Soils are zonal soils developed in areas located 40°N and 60°N and experience a cool temperate oceanic climate. When soils have not been able to fully develop due to climate or relief, intrazonal soils have developed.

Aspect 1 (Mineral Matter of BES and its Impact on BES Texture)

45% of Brown Earth Soil is composed of mineral matter. The mineral matter of Brown Earth Soil varies in Ireland due to different parent materials beneath it. Mineral matter has a huge impact on the characteristic of texture, which refers to the proportion of sand, silt and clay in it

Parent Material Influence on Brown Earth Soil Texture and Drainage Characteristics

• Brown Earth soils that formed over the glacial deposits of boulder clay have a loamy texture. A loam texture has roughly equal proportions of sand, silt and clay e.g. the Midlands and East of Ireland.

• This texture prevents Brown Earth soil in this part of Ireland from waterlogging in periods of rainfall, while during dry periods the soil never dries out.

• The presence of silt and clays which have extremely small pore spaces increase the water retention and hold onto moisture during summer droughts.

• Sand particles with their larger pore spaces prevent the soil from being waterlogged in times of heavy rain. This makes these Brown Earth soils ideal for cultivation e.g. wheat and barley in Co. Meath.

• Brown Earth soils that form over granite can lead to a slightly different texture however. When granite releases quartz into soil it can lead to a more sandy texture. This leads to decreased water retention and increased possibility of leaching in the soil e.g. Wicklow Mountains.

• Granite can also release clay into soil when feldspar is weathered by feldspar. This increases water retention in the soil, increasing the chance of waterlogging affecting the soil. Peat soil could now be created, also found in the Wicklow Mountains. A sandstone bedrock can lead to brown earth soils which have a sandy texture e.g. the Comeragh Mountains, Co. Waterford.

• This texture can lead to increased leaching and podzolisation which leads to impermeable hardpans being created. This can create podzolic brown earth soils.

Aspect 2 (Mineral Matter of BES and its Impact on BES pH, Colour and Minerals Solubility)

The mineral matter of Brown Earth Soil will also impact the characteristics of pH, colour, and the solubility minerals available for plants. The PH of brown earth soils vary from being slightly acidic to slightly alkaline, fertile brown earths have a brown colour, and mineral matter in the soil can be either soluble or insoluble

Bedrock Influence on Brown Earth Soil Fertility and pH

• The fertile Brown Earth Soils of the East of the Greater Dublin Area which formed over a bedrock of glacial deposits (boulder clay) have a neutral pH, brown colour and soluble minerals. This makes it fertile and ideal for arable farming and horticulture e.g. Lusk in Co. Dublin.

• Brown Earth soil that formed over the Comeragh Mountains in Waterford formed on sandstone rock. When sandstone is weathered, quartz (sand grains) is released into soil which is quite acidic. This will decrease the fertility of the soil as microbes cannot function in acidic conditions, and hence humus cannot be created.

• A similar acidity will be 39 found in brown earths formed over granite. When granite is weathered, it also releases quartz into soil. Brown earth soils that formed over limestone rock e.g. the midlands, will have calcium in them which is alkaline. Again, this could affect microorganisms ability to break down plant litter into humus as they cannot function in alkaline conditions

Mineral Effects on Brown Earth Soils

• Any brown earth soil that is either too acidic or alkaline may need fertilizer added to it to neutralize it in order to increase microorganism activity and hence fertility levels. The mineral matter of brown earth soil can also impact the solubility of the minerals it contains.

• For example, the brown earth soils that formed over limestone in the midlands contain calcium which is a soluble mineral and can be taken in easily by plant roots.

• These soils are suitable for the bloodstock industry e.g. Co. Kildare. Brown earth soils that formed over sandstone e.g. Waterford, contain quartz which is an insoluble mineral and cannot be taken in by plant roots. This can affect the fertility of soil.

• Finally, the mineral matter of Brown Earth Soil can also impact its colour. Due to the loamy texture of Brown Earths in the East of Ireland, the favourable drainage allows for microorganisms to thrive in their creation of humus, which will turn the soil a brown colour.

Aspect 3 (Organic Matter of BES)

Another component of Brown Earth Soil is organic matter, which generally makes up 5% of soil. Due to mostly forming under deciduous trees and the suitability of the climate, fertile Brown Earth soils have plenty of plant litter to create humus. This can impact the soils colour, water retention and overall fertility

Humus Formation and Climate/Vegetation Influence on Brown Earth Soils

• In the East of Ireland, deciduous trees are present which lose their leaves in Autumn. With an abundance of plant litter and suitable weather conditions, the microorganisms are able to decompose plant litter into humus which makes brown earth soils extremely fertile. Humus is a gel-like substance, full of nutrients and essential for plant growth. It is quite sticky so it binds soil together, which allows soil to hold and store water.

• This water mixes with humus making it possible for plant roots to take in this nutritional humus. Due to this binding of soil and storage of water, humus also prevents the loss of nutrients by leaching.

• The darker colour of brown earth soils also attracts heat better.

• This increased heat favours microorganisms who work better in hotter conditions. This will lead to increased levels of decomposition and higher humus levels in the soil.

• In areas where rainfall levels are higher and microorganisms do not have sufficient oxygen to transform plant litter into humus, brown earth soil development can be affected. For example, in the Wicklow Mountains which experiences more relief rainfall, waterlogging can impede humus creation and instead peat soils form. This is infertile soil.

• Also, in areas where coniferous trees are present, their pine needles are too acidic for microbes to decompose them into humus, so Podzolic Brown Earths can be created.

• With the lack of humus in these soils, pozolization can occur which leads to hardpans being created, and hence more waterlogging e.g. Co. Galway.

Draw a diagram of humufication

on doc

Aspect 4 (Water and Air Content of BES)

Other components of brown earth soils are water and air. Both generally make up 25% of soil. The proportion of each in Brown Earth Soil depends on texture, climate, humus content and relief. They allow a number of soil forming processes to take place e.g. leaching.

Humus Formation and Climate/Vegetation Influence on Brown Earth Soils

• Ireland’s Brown Earth Soils water content is hugely influenced by its climate.

• In the East of Ireland e.g. the Greater Dublin Area (GDA), it experiences the rain shadow effect so it receives less rainfall than the mountainous West of Ireland. With 700 mm of rainfall per year, this region experiences enough rainfall for minerals to be leached down through the soil towards plant and tree roots, though not too much as to leach them out of the soil completely.

• The loamy texture of fertile Brown Earth soils also ensures enough water storage for minerals to be dissolved for plant roots to take in, though not too much as to waterlog the soil.

• With brown earth soils abundant humus, this will also ensure water is stored in the soil and prevents further leaching of minerals.

• Sufficient drainage in the soil ensures brown earth soils have enough oxygen for microorganisms to breathe and decompose plant litter into humus

Relief and Climate Effects on Brown Earth Soil Development

• Due to the west of Ireland's mountainous relief, it experiences relief rain which impedes the development of brown earth soils.

• Rainfall levels can reach 2000mm in the West of Ireland. This will lead to increased leaching and podzolization, which will create hardpans in the soil. This occurs when rain leaches all minerals out of the soil except quartz.

• Iron and aluminium can accumulate in the B Horizon creating an impermeable hardpan. Podzolic brown earth soils will form as a result e.g. Co. Galway.

• This increased precipitation will also cause further waterlogging in the soil. This will impact an organism's ability to decompose organic material and peat soils may form as a result e.g. Co. Mayo.

• Air temperature also impacts brown earth soils development. In upland areas where the weather is colder e.g. Wicklow Mountains, microorganisms will not function as well and less decomposition of organic matter will take place.This will lead to less humus in the soil and decreased fertility levels.

• With a lack of humus, the rate of leaching increases which could lead to more podzolization and the development of podzolic brown earth soils.

Second diargram - impact of water on soil formation

on doc

Conclusion

To conclude, Brown Earth Soils characteristics differ based on aspects of their composition. The more fertile Brown Earth Soils have an abundance of humus in the East of Ireland, though Brown Earth soils development in the West of Ireland is impacted by increased climate and relief.