Soil

What is soil?

Soil is a $thin layer$ of material on the Earth’s surface

It’s a very important $natural resource$

Soil composition

1. [[Mineral Matter[[
2. ]]Air]]
3. {{Water{{
4. }}Humus}}
5. <<Living organisms<<

[[1. Mineral Matter[[

• $Main ingredient$ in soil
• $Weathered$ and $eroded$ $rock particles$
  • Stones
  • Sand
  • Silt
  • Clay
• Provides $minerals$ to help plants $grow$

]]2. Air]]

• Fills $spaces$ between rock particles
• Air contains $oxygen$ and $nitrogen$
  • plants need this to survive
• Needed by $living organisms$

{{3. Water{{

• Helps to $bind$ soil
• $Dissolves minerals$ so plants can $absorb$ them

}}4. Humus}}

• Forms when animals and plants $decay$ and rot
• $Jelly like substance$
• Provides $nutrients$
• Makes soil $fertile$

<<5. Living Organisms<<

• $Earthworms$
• $Bacteria$
• $Fungi$
• $Insects$
• $Burrowing animals$
• $Mix up$ the soil
  • Allow $air$ and $water$ to pass through the soil
• $Break down$ plants and animals => $organic material$

Soil texture

• What the soil $feels$ like
• Three groups:
  • $sand$
  • $silt$
  • $clay$
• Particles of $sand$ => $largest$
• Particles of $clay$ => $smallest$

Soil profiles

O Horizon

This layer contains $organic material$. Lots of $plant litter$ (leaves and rotting vegetation) which provides $humus$ for the soil

A Horizon

Upper layer of soil also known as $top soil$. Where $most$ of the $living organisms$ live. It’s $darker$ as it has the $highest humus content$, meaning it’s also the $most fertile$

B Horizon

Also know as $subsoil$. $Lighter$ in colour as it contains less humus however there is more $stones$ as it is located closer to the bedrock

C Horizon

This layer is called $bedrock$ or $parent material$. The $lower section$ is $solid rock$ but the $top section$ may be broken into $rock particles$

Leaching

1. Water passes through the soil when it $rains$
2. This washes $minerals$, $humus$ and $nutrients$ from the $A horizon$ to the $B horizon$

Most $plant roots$ are located in the A horizon, plants can’t access the minerals, humus and nutrient that are in B horizon which can affect their $growth$

In $extremely wet conditions$ minerals $build up$ between the two horizons. It becomes $cemented$ together to create an $impermeable layer$. Water can’t flow through making the soil above $water logged$

Brown Earth soils

• Most common soil type in Ireland
• Lowland areas
• Formed on boulder clay that was glacially deposited
• Loam => even mix of sand, silt and clay
• Ideal for crops
• Deciduous forests
• Lots of humus => fertile
• Very little leaching

Influence of soil on vegetation

Depth

• $Deep$ fertile soils => support a $wide variety$ of crops => $high nutrient content$
• $Shallow$ infertile soils => $limited$ type of vegetation

Acidity

• Some plants such as $rhododendrons$ grow in $acidic soil$
• $Not many$ plants grow in acidic soil
• $Lime$ => spread on land => $reduce acidity$ => $increase fertility$

Drainage

• $Clay$ soil => easily $waterlogged$ => $difficult$ to cultivate
• $Sand$ soils => $well drained$ => support a $wide range$ of crops

Influence of vegetation on soil

Plant litter

• $Vegetation$ => $plant litter$ => $humus$ => $fertile$ soils
• Soil under $deciduous$ trees are $more fertile$ because there is $more plant litter$

Soil erosion

• $Bind$ and $protects$ soil from $mass movement$
• When the $vegetation$ is $lost$ it becomes $vulnerable$ to $erosion$

Leaching

• Vegetation acts as an $umbrella$ against rain
• $Less water gets into the soil$ => $less leaching$

Human interference with soil

1. Deforestation

Cutting down of trees for $economic purposes$

Two major effects:

1. Removal of trees $reduces plant litter$ => $soil loses fertility$
2. Exposure of soil can lead $erosion$, $flooding$ and $mass movement$
   • $Flooding: low land areas$
   • $Mass movement: Up land areas$

==Solution==: $Forest management$ and $reforestation$ (plant of trees)

2. Intensive farming

Lead to $desertification$ => $expanding of desert$

==Example==: The Sahel

1. Over-cropping
   • Crop $continuously$ grown on land => $nutrients removed$ => soil becomes $exhausted$
     • Mainly by $mono culture$ (1 type of crop) and $cash crops$
     • Example: $coffee$ or $cotton$
   • ==Solution==: $Careful management$ and $crop-rotation$
2. Overgrazing
   • $Too many livestock on a piece of land$ => $intensive grazing$ => $vegetation and roots destroyed$
   • Soil is left open and $vulnerable to erosion and weathering$
   • ==Solution==: $changing farming practices$ and $education$