Understanding Soil Profiles in Agricultural Science

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Soil Profiles
 
Leaving Cert. Agricultural Science
 
Classification
 
Soil profiles are a useful method of classifying soils.
Soil profiles are determined by examining
the proportions of each ‘horizon’ and
The colour of each horizon
For your leaving cert exam there are 3 main profiles to know:
Brown Earth
Podzol
Gley
Students are expected to draw each profile for the exam
 
Drawing a soil profile
 
As for any diagram in the exam, give yourself at least half a page
Use pencil
You can use colour but this isn’t a good idea if you are against time
The examiner is looking for correct proportions, and correct labels to indicate
colours.
 
Horizons
 
O – Organic horizon
This is topmost layer, made of
vegetation, humus, etc.
A – Top soil
A horizon is a mixture of mineral
and organic particles
Most important layer
Size of A determines the quality of
a soil
B – Sub soil
Mineral matter mostly: sand, silt,
and clay
C – Bedrock / Broken rock
 
Brown Earth
Thick O horizon, i.e. plenty of
humus in soil
 
Brown earths have an even distribution of organic
And mineral particles, this leads to the uniform
brown colour in each horizon
 
Podzol
Black O Horizon due to acidic leaf litter
Bleached (not as brown) A Horizon due to
leaching of minerals
Iron pan formed between A + B horizons.
Due to the accumulation of Iron and
Aluminium from top soil. Impermeable to
water and plant roots
 
Note that the proportions for Brown Earth and Podzol soils are the same,
when drawing them in the exam it’s easy to remember the only structural
Difference is the iron pan
 
Gley Soils
Very narrow O horizon – key difference in the
formation of gley vs. bog (a lot of organic matter)
A Horizon very thin – little to no organic matter,
bleached/grey in colour
B Horizon is incredibly large by comparison to Brown
Earth and Podzol. It has a mottled blue/green
appearance due to anaerobic bacteria. This will turn
orange/red if exposed to oxygen
 
Study advice
 
Go back through exam papers and practice drawing each of the three soil
profiles.
Check the marking scheme to see how many marks are awarded in each case.
Remember when drawing, use at least half a page and make notes/labels very
clear
Use pencil in case you make a mistake
Watch your time in the exam
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Soil profiles are essential for classifying soils, with main profiles being Brown Earth, Podzol, and Gley. It's crucial to draw these profiles accurately for exams, considering horizons like O Horizon, A Horizon, B Horizon, and Bedrock. Brown Earth has a thick O horizon with uniform brown color, Podzol has a black O horizon due to acidic leaf litter, and Gley soils feature a mottled blue/green appearance. Practice drawing these profiles for better understanding and exam preparation.


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  1. Soil Profiles Leaving Cert. Agricultural Science

  2. Classification Soil profiles are a useful method of classifying soils. Soil profiles are determined by examining the proportions of each horizon and The colour of each horizon For your leaving cert exam there are 3 main profiles to know: Brown Earth Podzol Gley Students are expected to draw each profile for the exam

  3. Drawing a soil profile As for any diagram in the exam, give yourself at least half a page Use pencil You can use colour but this isn t a good idea if you are against time The examiner is looking for correct proportions, and correct labels to indicate colours.

  4. Horizons O Organic horizon This is topmost layer, made of vegetation, humus, etc. A Top soil A horizon is a mixture of mineral and organic particles Most important layer Size of A determines the quality of a soil B Sub soil Mineral matter mostly: sand, silt, and clay C Bedrock / Broken rock

  5. Brown Earth Thick O horizon, i.e. plenty of humus in soil Brown earths have an even distribution of organic And mineral particles, this leads to the uniform brown colour in each horizon

  6. Podzol Black O Horizon due to acidic leaf litter Bleached (not as brown) A Horizon due to leaching of minerals Iron pan formed between A + B horizons. Due to the accumulation of Iron and Aluminium from top soil. Impermeable to water and plant roots Note that the proportions for Brown Earth and Podzol soils are the same, when drawing them in the exam it s easy to remember the only structural Difference is the iron pan

  7. Gley Soils Very narrow O horizon key difference in the formation of gley vs. bog (a lot of organic matter) A Horizon very thin little to no organic matter, bleached/grey in colour B Horizon is incredibly large by comparison to Brown Earth and Podzol. It has a mottled blue/green appearance due to anaerobic bacteria. This will turn orange/red if exposed to oxygen

  8. Study advice Go back through exam papers and practice drawing each of the three soil profiles. Check the marking scheme to see how many marks are awarded in each case. Remember when drawing, use at least half a page and make notes/labels very clear Use pencil in case you make a mistake Watch your time in the exam

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