Published on March 2, 2014
Irish Brown Earth Soils Geoecology
Exam Brief Typical Exam Question: “Examine the development of an Irish soil that you have studied.”
Irish Soils Despite its small size, Ireland has a variety of soils. Brown earths are the most common soil type. They are mainly found in the centre of Ireland.
Irish Soils There are 4 main types of soil in Ireland: 1. 2. 3. 4. Brown soils Podzol Soils Peaty Soils Gley Soils
Soil Profile: Brown Earth Soil No distinct horizons – uniformly brown in colour. This is due to the climate which encourages the presence and activity of worms and beetles in the soil. These mix the soil up and remove any horizons that may form due to leaching and humification.
Factors influencing brown earth soils in Ireland: Climate Relief Living organisms / vegetation Parent material Time
Climate Brown earth soil has developed in response to Ireland’s cool maritime climate. Temperature averages 15ºC in July to 6ºC in January. Soil temperature rarely cold enough to stop biological activity completely. Rainfall average 1500 mm per year. Climate encourages year round bacteria, earthworm and fungi activity. Brown earth soils are found where soil temperatures are above 0ºC for 9 months of the year.
Relief Relief influences (1) depth and (2) drainage of this soil. Brown earth soils formed on slopes tend to be thinner and well drained - mass movement creates deep soils at the base of slopes. In soils formed on colder higher ground there is less animal activity and less humus is formed than in soils formed on warmer lowlands. Aspect: South-facing slopes have warmer soils than north-facing so agriculture is often possible on slopes with a southerly aspect.
Living organisms / Vegetation • Brown earth soils develop under deciduous forests (e.g. oak, ash, chestnut, birch). • The top horizon has a thick layer of dark rich humus due to the accumulation of leaves during autumn. • Due to the mild climate micro-organisms such as bacteria and fungi are active for at least 9 months of the year adding to the fertility of soil. • Animals like badgers and rabbits burrow into the soil, churning it up and removing horizons.
Parent Material The parent material, or bedrock, is usually boulder clay deposited during the last ice age. Local changes to parent material have created three variations (intrazonal) in brown earth soil: A. B. C. Acidic brown earths – 500m above sea level on crystalline rock (e.g. granite, sandstone) Shallow brown earths – in limestone areas such as Burren Podzols – slightly leached, occur on glacial drift of Irish lowlands.
Time These brown earth soils have developed since last ice age over 10,000 years ago. They are mature, well developed soils but have local variations depending on slope, aspect and drainage.
Characteristics of brown earth soils in Ireland: COLOUR Brown in colour due to: Presence of humus which makes it appear dark. Action of leaching which washes some nutrients out of soil so that it is not too dark brown in colour.
Characteristics of brown earth soils in Ireland: pH Varies from slightly alkaline to slightly acidic due to temperate climate and variations in parent material. Living things thrive in this pH.
Characteristics of brown earth soils in Ireland: Humus Content Brown earth soils are rich in humus because the natural vegetation in Ireland is deciduous forest.
Characteristics of brown earth soils in Ireland: Structure Brown earth soils have a well developed crumb structure that provides pore spaces for air and water, encouraging plant growth.
Characteristics of brown earth soils in Ireland: Texture Generally have a loam texture due to presence of variety of parent materials (e.g. sandstone and shale).
Characteristics of brown earth soils in Ireland: Water Content Depends on local conditions of relief and drainage. Because of its generally loam texture and crumb structure, these soils are not too wet or dry. They have a water content that encourages plant growth.
Processes affecting formation of brown earth soils in Ireland: 1. Humification 2. Leaching
Humification Cool temperate oceanic climate encourages humification all year long. Rate of humification: Decreases in winter Speeds up in summer The presence of large amounts of humus adds to soil’s fertility.
Leaching Year round rainfall causes moderate amounts of leaching in brown earth soils. This adds to soil fertility by gently washing nutrients down to the soil. Waterlogging can occur in poorly drained areas causing brown earth soils to become gleys.
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Irish Brown Earth Soils To be studied as part of Optional Unit 7 for Higher Level Leaving Cert Geography.
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