Irish brown earth soils


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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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Irish brown earth soils

  1. 1. Irish Brown Earth Soils Geoecology
  2. 2. Exam Brief Typical Exam Question: “Examine the development of an Irish soil that you have studied.”
  3. 3. 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.
  4. 4. Irish Soils There are 4 main types of soil in Ireland: 1. 2. 3. 4. Brown soils Podzol Soils Peaty Soils Gley Soils
  5. 5. 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.
  6. 6. Factors influencing brown earth soils in Ireland:  Climate  Relief  Living organisms / vegetation  Parent material  Time
  7. 7. 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.
  8. 8. 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.
  9. 9. 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.
  10. 10. 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.
  11. 11. 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.
  12. 12. 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.
  13. 13. 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.
  14. 14. 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.
  15. 15. 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.
  16. 16. 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).
  17. 17. 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.
  18. 18. Processes affecting formation of brown earth soils in Ireland: 1. Humification 2. Leaching
  19. 19. 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.
  20. 20. 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.