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Soil Geography and Formation, Lecture notes of Physical Geography

Santa Monica CollegePhysical Geography

An in-depth exploration of soil geography, focusing on soil profiles, components, and forming factors. It delves into the parent material, climate, biological activity, relief, and time's role in soil formation. The document also covers soil properties such as texture, color, structure, chemistry, and consistency, as well as soil profiles and their development.

Typology: Lecture notes

2022/2023

Uploaded on 03/29/2024

illusivemonkey
illusivemonkey 🇺🇸

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Soil Geography
Soil Geography and Soil Profiles:
Parent material for the soil is underlying geologic material.
Climate and biological activity influence the soil development.
Relief and Topography affect soil formation.
Soil And Regolith:
Soil – thin surface layer made of inorganic and organic materials.
oMineral particles, organic matter, gases, and liquid.
oInterface between atmosphere, hydrosphere, biosphere, and lithosphere.
oThe surface is always almost covered by soil.
oProduce and stores nutrients for plants
oDevelopment begins with the breaking of rock at the surface along with water
Regolith – Layer of broken rock and partly decomposed rock particles that covers
bedrock
oLarger pieces closer to bedrock
oCan come from other places
oUpper layer is plants and their material, microscopic animals, and air and water
Soil Forming Factors:
Geologic
oParent material – Bedrock or Transported Sediment
oYounger soild more representative of parent material
Climatic
oTemperature and moisture are biggest factors
oChemical and biological processes affected by T and M
oMovement of water carries chemicals and rearranges components of the soil
Topographic
oSlope and drainage
oFlat surfaces = Deeper soil
oSteep slopes = Soil erosion = Thin soil
oPour drainage leads to high organic matter and less air
Biological
oContain living organisms and organic matter
oPlants contribute to soil development
Plant roots – aeration
Animals – compact soil
Bioturbations – mixing activity of animals
Earthworms – soil structure, fertility, lower erosion, deeper soil
Microorganisms – decomposition
Time
oSoil formation = slow
oFormation depends on parent material/environmental characteristics
oDegradation happens faster than development
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Soil Geography

Soil Geography and Soil Profiles:  Parent material for the soil is underlying geologic material.  Climate and biological activity influence the soil development.  Relief and Topography affect soil formation. Soil And Regolith:  Soil – thin surface layer made of inorganic and organic materials. o Mineral particles, organic matter, gases, and liquid. o Interface between atmosphere, hydrosphere, biosphere, and lithosphere. o The surface is always almost covered by soil. o Produce and stores nutrients for plants o Development begins with the breaking of rock at the surface along with water  Regolith – Layer of broken rock and partly decomposed rock particles that covers bedrock o Larger pieces closer to bedrock o Can come from other places o Upper layer is plants and their material, microscopic animals, and air and water Soil Forming Factors:  Geologic o Parent material – Bedrock or Transported Sediment o Younger soild more representative of parent material  Climatic o Temperature and moisture are biggest factors o Chemical and biological processes affected by T and M o Movement of water carries chemicals and rearranges components of the soil  Topographic o Slope and drainage o Flat surfaces = Deeper soil o Steep slopes = Soil erosion = Thin soil o Pour drainage leads to high organic matter and less air  Biological o Contain living organisms and organic matter o Plants contribute to soil development  Plant roots – aeration  Animals – compact soil  Bioturbations – mixing activity of animals  Earthworms – soil structure, fertility, lower erosion, deeper soil  Microorganisms – decomposition  Time o Soil formation = slow o Formation depends on parent material/environmental characteristics o Degradation happens faster than development

o Can be formed and reformed Soil Components:  Inorganic Material o Mineral matter – Small particles and dissolved minerals o ½ of soil is sand or silt in minerals o Clay is the smallest particle – Silicate  Organic Material o Small portion – Big impact  Living, dead, decomposing, or decomposed organisms  Living organisms – rearranging and aerating soil o Litter: leaves, twigs, stalks, and other dead plants accumulate on surface o Humus remains: gelatinous organic matter from decomposed residue  Root development, chemical reactions, reservoir for water  Soil Air o ½ average soil = pore spaces o Average soil = ½ air, ½ water o High in CO2 low in oxygen  Soil Water o Rainfall and snowmelt o Pulls groundwater above water table o Water fills pore spaces o Lost as it percolates or by evaporation/transpiration  Four Forms of Soil Moisture o Gravitational – infiltration from above o Capillary – Moisture held within soil particles at surface o Hygroscopic water – Small film of water bound to soil particles o Combined water – Help in chemical combination with soil minerals  Soil Water Processes o Field Capacity – Remaining water fills pores after gravitational water has drained o Wilting Point – Plants cant extract water from soil o Leaching – Water dissolves and carries nutrients into soil (depletes topsoil) o Eluviation – Water percolates into soil and carries particles downwards o Illuviation – Deposition of particles at lower levels  Soil Water Balance: Relationship along gain, loss and storage o Water added by percolation, lost by evapotranspiration o Determined by temp and humidity  Increased evapotranspiration caused by warm weather o Soil water budget – Variation in soil water balance over time Soil Properties:  Texture o Many particles of various sizes o Separates: size groups in the classification of soil sizes  Smaller separates are fragments of weathered parent material  Coarser particles are inert materials

 attachments so that nutrient cations do not get leached away  colloidal complex made of colloid and attached cations  if bond too strong, nutrients cannot be reached by plants o cation exchange capacity (CEC): capability of soil to attract and exchange cations  the higher the CEC, the more fertile the soil  Clay and humus with high CEC activity o  Consistence o Wet = sticky moldable o Moist = loose to friable to firm o Dry = brittle rigid, loose to soft to extremely hard  Acidity and alkalinity o Acids and bases are chemical solutions that produce certain ions when dissolved in water. o Nearly all nutrients for plants come from solutions.  Overly alkaline soil solutions inefficiently dissolve minerals.  Highly acidic soil solutions overly dissolve nutrients. o Optimum soil solution for plants would be neutral. o pH scale describes quantity of hydrogen atoms. Soil Profiles:  Soil horizons o horizons: distinctly recognizable layers, each with different characteristics o positioned approximately parallel with land surface o each layer separated by transition zones o soil profile: a vertical cross section from surface down through soil layers into parent material  Well-developed soil profile o O horizon: surface layer of organic matter. Undecomposed litter, decomposed organic debris, and humus o A horizon: topsoil, a mineral horizon.  A leached mineral horizon with a high portion of organic matter (dark in color) o E horizon: eluvial layer of sand or silts.  A light-colored layer representing the zone of maximum leaching o B horizon: subsoil illuviation layer.  Maximum zone of accumulation of weathering products such as silicate clay, iron, aluminum, humus, carbonates, gypsum, or silica o C horizon: regolith layer, lacks organic matter.  Relatively unaltered unconsolidated parent material o R horizon: bedrock with little evidence of weathering  Solum: "true" soil with O, A, E, B horizons  Soil profile development o Time is key passive factor. o Water is vital active factor.  without water, no profiles

 material carried by water from surface downward by eluviation and leaching  idealized soil development o All horizons would develop on well- drained, gentle slopes in undisturbed environment. o Typically, soil profiles have a well- developed horizon and variation in other horizons. o Immature soils contain A horizon over C horizon.