Monday, Oct. 4SoilsSoil: DefinitionSoil ProductionSoil Production: InputsSoil Production: OutputsSoil Thickness: StorageFactors of Soil FormationFactors of Soil FormationFactors of Soil FormationFactors of Soil FormationFactors of Soil FormationFactors of Soil FormationFactors of Soil FormationFactors of Soil FormationProcesses of Soil DevelopmentAdditions to soilsTransformationsSlide Number 19Slide Number 20Slide Number 21Slide Number 22Soil Horizons and ProfilesTypical soil profileCookport soil, PennsylvaniaSoil classification = messySoil classification = soil ordersSoil classification = soil ordersSoil types (more simply) – AridisolsSoil types – OxisolsDecomposing organic material from plants and animals mixes with accumulated soil minerals. Limits on soil developmentRates of Soil DevelopmentSoil and the Life-Cycle of CivilizationsSlide Number 35Slide Number 36Slide Number 37Monday, Oct. 41. Field trip A1 & A2 signups: make sure you are where you think you should be…2. 5 credit people, field trip introduction in lab today1. If you are unable to attend THIS SATURDAY, let Aaron know by 5PM TODAY2. You will get a ZERO for the field trip if you do not participateSoilsWe know more about the movement of celestial bodies than about the soil underfoot.- Leonardo da VinciSoil: Definition• Solid earth material that has been altered by physical, chemical and organic processes so that it can support rooted plant life.• Engineering definition: Anything that can be removed without blastingSoil ProductionSoil Production: InputsConversion of rock to soilSoil Production: OutputsDownslope movement of soilSoil Thickness: Storageinput ± output = soil thicknessor: rock conversion ± soil transport = thickness that is, soil thickness reflects the balance between rates of soil production and rates of downslope soil movement.• Slope• Weathering RateFactors of Soil Formation• Climate• Organisms• Parental Material• Topography• TimeFactors of Soil FormationClimate• Temperature and precipitation• Indirect controls (e.g., types of plants)• Weathering ratesThe greater the rainfall amount, the more rapid the rate of both weathering and erosion.Factors of Soil FormationOrganisms• Types of native vegetation• Weathering is dependent of plant growth• Plant and animal activity produces humic acids that are powerful weathering agents. [acids derived from chemical breakdown of organic matter]• Plants can physically as well as chemically break down rocks. • Plants stabilize soil profiles, Animals (including humans) tend to increase erosion.Factors of Soil FormationParent Material• Chemistry• Mineralogy • Grain sizeFactors of Soil FormationTopography:• Ground slope• Elevation• Aspect (north vs. south facing slopes)Downslope transport of soil is a function of slope:Erosion rate = f(S)Steeper slopes erode faster. The steeper the surface slope, the more likely any eroded material is to be transported out of the system.Factors of Soil FormationSoils on hillslopes reach an equilibrium thickness, often about 1m.Soils on flat surfaces, such as floodplains or plateaus, tend to thicken through time due to weathering rates being greater than sediment transport rates.Factors of Soil FormationFactors of Soil FormationTime for development and destruction of soil profilesTypical chemical reaction rates are slow the longer a rock unit has been exposed, the more likely it is to be weatheredAnd, the longer soil waits before transport, the thicker it can become…Processes of Soil Developmentcombined effects of:• additions to ground surface• chemical transformations• vertical transfers• removals from soilrelative importance variesAdditions to soilsInputs from outside ecosystemAtmospheric inputsPrecipitation, dust, depositionHorizontal inputsFloods, tidal exchange, erosion, land- water movementInputs from within ecosystemLitterfall and root turnoverTransformationsDecomposition of organic matterBreakdown to form soluble compounds that can be absorbed leached awayDepends on input quantity, location (roots, leaves), environment (temp & precip)Humification to form complex organic matterWeathering of rocksPhysical weathering / fragmentation of rockFreeze-thaw; drying-wetting; fireChemical weatheringprimary secondary mineralsParent material (bedrock) undergoes weathering to become regolith (soil + saprolite).Soil is a mixture of mineral and organic matter lacking any inherited rock structure.SoilSaprolite is weathered rock that retains remnant rock structure. SaproliteSaproliteSoil Horizons and ProfilesSoil Horizonsover time, soil layers differentiate into distinct ‘horizons’not deposited, but zones of chemical action• Chemical reactions and formation of secondary minerals (clays). • Leaching by infiltrating water (elluviation)• Deposition and accumulation of material leached from higher levels in the soil (illuviation) Soil ProfileSuite of horizons at a given localityTypical soil profileCookport soil, PennsylvaniaC HorizonB HorizonA HorizonSoil classification = messySoil classification = soil ordersAridisols = arid zone soils (calcic horizons)Mollisols = grassland soils (thick A horizon)Alfisols, Ultisols, and Spodosols = forest soils (thick B horizon)Oxisols = tropical soils (quite oxidized)Histosols = wetland soilsGelisols = polar soilsAndosols = volcanic parent materialVertisols = swelling claysEntisols = weak A over C horizonInceptisols = weak B horizonAridisols = arid zone soils (calcic horizons)Mollisols = grassland soils (thick A horizon)Alfisols, Ultisols, and Spodosols = forest soils (thick B horizon)Oxisols = tropical soils (quite oxidized)Histosols = wetland soilsGelisols = polar soilsAndosols = volcanic parent materialVertisols = swelling claysEntisols = weak A over C horizonInceptisols = weak B horizonSoil classification = soil ordersSoil types (more simply) – AridisolsPhysical weathering breaks rocks into small mineral particles.Soil types – OxisolsChemical weathering dissolves and changes minerals at the Earth’s surface.Decomposing organic material from plants and animals mixes with accumulated soil minerals.Soil types – MollisolsLimits on soil developmentBalance Between: Downward Lowering of Ground Surface Downward Migration of Soil Horizons If erosion rapid or soil evolution slow, soils may never mature beyond a certain point Extremely ancient soils may have lost
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