SoilsPowerPoint PresentationSoil: DefinitionSoil ProductionSoil Production: InputsSoil Production: OutputsSoil Thickness: StorageFactors of Soil FormationSlide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18DecompositionSoil Horizons and ProfilesSoil ProfilesSlide 22Cookport soil, PennsylvaniaPhysical weathering breaks rocks into small mineral particles.Chemical weathering dissolves and changes minerals at the Earth’s surface.Decomposing organic material from plants and animals mixes with accumulated soil minerals.Slide 27Slide 28Slide 29Slide 30Limits of Soil DevelopmentRates of Soil DevelopmentErosion of Natural CapitalSoil and the Life-Cycle of CivilizationsSlide 35Slide 36SoilsWe 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: StorageSoil 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 erosion and leaching.Factors of Soil FormationOrganisms• Types of native vegetation• Weathering is dependent of plant growth• Plant and animal activity produces humic acids that are powerful erosion agents. • Plants can physically erode as well as chemically erode. • Plants stabilize soil profiles, Animals (including humans) tend to increase erosion.Factors of Soil FormationParental Material:• Chemistry• Mineralogy • Grain sizeFactors of Soil FormationTopography:• Ground slope• Elevation• Aspect (e.g., north facing vs. south facing slopes)Downslope transport of soil is a function of slope: • Erosion rate = f(S)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 1 m.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• Development and destruction of soil horizons• Reaction rates are slow, the longer a rock unit has been exposed, the more likely it is to be weathered.Soil Development•Inputs from outside ecosystem–Atmospheric inputs•Precipitation, dust, deposition–Horizontal inputs•Floods, tidal exchange, erosion, land-water movement•Inputs from within ecosystem–Litterfall and root turnoverAdditions to Soils•Decomposition of organic matter•Humification to form complex organic matter•Weathering of rocks to produce more stable forms–Physical weathering•Fragmentation of rock–Freeze-thaw; drying-wetting; fire•Physical abrasion–Abrasion by glaciers–Chemical weathering•Dissolves primary minerals•Forms secondary mineralsTransformations•Breakdown of soil organic matter to form soluble compounds that can be absorbed or leached•Depends on –Quantity of input–Location of input (roots vs. leaves)–Environment•Temperature•moistureDecompositionSoil Horizons•Layers in Soil•Not Deposited, but Zones of Chemical ActionSoil Profile•Suite of Layers at a Given Locality Soil Horizons and ProfilesSoil ProfilesOver time different levels of a soil can differentiate into distinct horizons that create soil profiles.• Chemical reactions and formation of secondary minerals (clays). • Leaching by infiltrating water.• Deposition and accumulation of material leached from higher levels in the soil.Soil ProfilesCookport soil, PennsylvaniaC HorizonB HorizonA HorizonPhysical weathering breaks rocks into small mineral particles.Chemical weathering dissolves and changes minerals at the Earth’s surface.Decomposing organic material from plants and animals mixes with accumulated soil minerals.Parent material (solid rock) 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. SaproliteSaproliteBalance Between: •Downward Lowering of Surface •Downward Migration of Horizons If erosion rapid or soil evolution slow, soils may never mature beyond a certain point. Extremely ancient soils may have lost everything movableLimits of Soil DevelopmentRates of Soil DevelopmentU.S. Department of Agriculture estimates that it takes 500 years to form an inch of topsoil. That’s less than 0.01 mm yr-1Erosion of Natural CapitalModern rates of soil loss are 100 to 1000 times rates of soil formation (typically mm yr-1 to cm yr -1 in agricultural settings).Sets up a fundamental problem due to the erosion of natural capital!Soil and the Life-Cycle of CivilizationsHow long would it take to erode 1 m thick soil?Thickness of soil divided by the difference between Rate of soil production and erosion. 1 m = 100 to 1000 years(1mm to 1cm) - (.01 mm)This is about the life-span of most major civilizations...Man—despite his artistic pretensions, his sophistication, and his many accomplishments—owes his existence to a six-inch layer of topsoil and the fact that it rains.- Author UnknownNational Archives: 114 SC 5089A nation that destroys its soils, destroys itself. – President Franklin D. Roosevelt, Feb. 26,
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