SOIL AND SOIL FORMATION - LACOE Moodle AND SOIL FORMATION Soil is a mixture of parent rock, decayed organic matter, minerals, water and air. ... Soil pH Soil color Soil structure

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Post on 07-Mar-2018




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  • SOIL AND SOIL FORMATIONSoil is a mixture of parent rock,decayed organic matter, minerals,water and air.

    It takes thousands of years to form.

  • Factors affecting soilformation

    Climate (Temperature and Humidity) Slope of land (topography) Type of parent material (rock type) Type of vegetation growing on the soil Time

  • Soil formation

    1. Weatheringa) Chemical weatheringb) Mechanical weathering

    2. Decomposition of organic matter (plantand animal remains)

  • Mechanical Weathering

    Weathering breaks the rock into to smallerpieces called sediment. (sand, silt andclay)

  • Mechanical Weathering

    Mechanical weathering includes: growingplants between rock, ice wedging andburrowing animals.

    Temperature changes can break rocksapart.

    Where is mechanical weathering mostimportant? Why?

  • Which biome(s) have themost important mechanicalweathering and why?

    In temperate climates, winter is coldenough for water to turn into ice. Icecan crack rocks into little pieces

    In the desert, the temperature changesgreatly each day. This cracks the rocks.

  • Chemical Weathering

    The chemical composition of the rockschanges in chemical weathering becausechemical reactions occur.

    Natural acids, such as carbonic acid in rainand plant acids cause chemical weathering.

    Oxygen in the air causes oxidation.

    Why is chemical weathering is important inwarm, humid climates?

  • Why is chemical weathering isimportant in warm, humidclimates? Chemical reactions are faster when the

    temperature is higher.

    Chemical reactions are faster in solution

    Chemical weathering is very important inTropical climates.

  • Oxidationreactions oftropical soilcause it tobe reddishin color.

  • Properties of soil that changequickly Temperature

    Moisture content

    Composition of air in the soil pores

  • Properties of soil that changeover months or years Soil pH Soil color Soil structure Organic content in the soil Fertility of the soil Microorganisms Density

  • Properties that change overhundreds or thousands of years

    Mineral composition of the soil Particle size in the soil Horizon formation

  • Soil Horizons

    O horizon surface litter (leaves and twigs) A horizon topsoil layer (contains humus) B horizon subsoil (inorganic) C horizon bedrock and parent material E horizon forms when the conditions are

    wet or forested (eluvial horizon) lighter incolor

    R horizon: A rock layer that is sometimesunder the soil profile

  • Identify O, A, B, C and E

  • Soil profile from a temperateforest in Jordan

  • Soil Profile from Buenos Aires,Argentina

  • More about soil profiles

    Sometimes, not all of the horizons will bepresent in some soils.

    For example, O and E are only in forestedareas

    Agricultural, deserts and grassy areas willstart with an A horizon but do not have anE horizon.

    If the area was eroded, the A horizon maybe gone!

    Shallow soils might not have the B horizon.

  • Soils around the world

    Grassland soils Forest soils Tropical soils Cold climate soils (tundra) Arid soils Wet soils

  • Grassland Soils Common in Midwest

    of the USA, Argentinaand Ukraine

    Deep and dark Good for crops High organic content Holds water and


  • Soil Profile fromPennsylvania, USA

  • Soil Profile from Buenos Aires,Argentina

  • Coniferous forest soils

    The organicmatter comesfrom leavesand roots oftrees.

    The acidsfrom the rainand leavesform acidswhich leachmaterialsfrom the tophorizons.

  • Tropical Soils The soil is deepand bright red(iron oxides)

    The horizons arehard to tell apart

    Organic matterdecomposes veryquickly andtransforms intoinactive materialthat binds to clay

    Nutrients areleached from thesoils

  • Tropical Soil 3 hours fromBangkok, Thailand

  • Tropical Soil from Ghana

  • Tundra soils The soil is not

    very developedand only faintindications ofhorizons canbe seen.

    Permafrost canbe seen at thebottom of theprofile

  • Arid soil

    The A horizon is light brown because thereis a lack of organic matter or moisture.

    The organic matter is not returned to thesoil because there are not very many plants

    When it rains, materials are carrieddownward into the profile to the B horizon

    Calcium carbonate accumulates over timeand becomes hard

  • Wet soil

    The A horizon is dark from accumulationof organic matter.

    The soil is saturated and not enoughoxygen is present to decompose theorganic matter.

    The B horizon is grayish.

  • Poor soil use leads todesertification


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