lecture 7, soil development - stanford...
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Lecture 7, Soil Development
GES175, Science of Soils
Parent Material → Soil
primaryprimary secondarysecondarymineralsminerals mineralsminerals
Rock
Entisol
Inceptisol
Alfisol
Ultisol
Oxisol
Mollisol
Spodosol(cool and wet)
Aridisol (dry climate)Vertisol (clay mineralogy)
Ideal Weathering Series
Soil Formation
Five Soil Forming Factors:
Climate
Biota
Topography
Parent Material
Time
Soil FormationSoil Formation
ClimateClimate–– Arid: Arid: Minimal leaching, slow dissolutionMinimal leaching, slow dissolution–– Humid: Humid: Extensive leaching, rapid Extensive leaching, rapid
dissolutiondissolution–– Cool: Cool: Active physical weathering, slow Active physical weathering, slow
chemical weathering. Buildup of OM.chemical weathering. Buildup of OM.–– Warm: Warm: Strong chemical weathering, rapid Strong chemical weathering, rapid
OM decay (nutrient cycling)OM decay (nutrient cycling)
Soil FormationSoil FormationBiotaBiota–– Diversity and activityDiversity and activity–– Plant canopyPlant canopy
Root exudates promote weathering Root exudates promote weathering Grasslands: Base Grasslands: Base cationscations, humus, humus--mineral mineral interaction (strong A horizon).interaction (strong A horizon).Forest: Lower base saturation, less humusForest: Lower base saturation, less humus
–– Confers: low B.S., less incorporated OMConfers: low B.S., less incorporated OM–– Deciduous: Higher B.S., more OMDeciduous: Higher B.S., more OM
Soil FormationSoil FormationTopography: Slope and Aspect
NColdWet
WarmerDrier
Shallow Soils
Deep Soils
Finer Texture
Less Developed
More Developed
More Clay
Soil FormationSoil FormationTimeTime–– RecentRecent
Little profile developmentLittle profile development–– Weakly weatheredWeakly weathered–– Little clay movementLittle clay movement
Primary minerals presentPrimary minerals present
–– OldOldWellWell--developed horizonsdeveloped horizonsSecondary mineralsSecondary minerals
Soil FormationSoil FormationParent MaterialParent Material–– Solid RockSolid Rock
Basalt (Basalt (maficmafic))–– High base saturationHigh base saturation
Granite (Granite (felsicfelsic) ) –– Lower base saturationLower base saturation
–– Transported MaterialTransported MaterialAlluviumAlluviumColluviumColluviumEolianEolian
Parent Material: Transported Parent Material: Transported AgentAgent DepositDepositgravity gravity -------------------------- ColluvialColluvialwater water ------------------------------ AlluvialAlluvial
MarineMarineLacustrineLacustrine
ice ice ---------------------------------- Glacial (till, moraine)Glacial (till, moraine)wind wind ---------------------------------- EolianEolian
Wide diversity within Wide diversity within
groupsgroups
-Energy of water determines size of particles transported
-Flood plains, terraces (old flood plains), deltas are rich, fertile soils (typically)
-Alluvial fans are coarser in texture but remain productive
Alluvial depositsAlluvial deposits
Boise Valley
First Terracelooking north from second terrace
Pleistocene Ice AgePleistocene Ice Age1. Major influence on soil materials1. Major influence on soil materials
2. Glacial till and moraines2. Glacial till and moraines(a) highly variable and heterogeneous(a) highly variable and heterogeneous(b) properties reflect source(b) properties reflect source
3. Glacial outwash and 3. Glacial outwash and lacustrinelacustrine depositsdeposits(a) streams from glacial melt = alluvium(a) streams from glacial melt = alluvium(b) lakes formed, when dried = (b) lakes formed, when dried = lacustrinelacustrine
Process of Soil FormationProcess of Soil Formation
TransformationsTransformations–– Mineral weathering, OM Mineral weathering, OM decompdecompTranslocationsTranslocations–– Transport of inorganic and organic materialTransport of inorganic and organic materialAdditionsAdditions–– OM, particles (OM, particles (eolianeolian, , aluvialaluvial, , colluvialcolluvial))LossesLosses–– ErosionErosion–– LeachingLeaching
Impact of MacroImpact of Macro--organismsorganisms
Translocations (Soil Mixing)
Natural Soil Mixing
Earthworms, Gophers, Moles,Ants, Termites, Cicadas
Channeling Water
‘piping’
Parent Material → Soil
primaryprimary secondarysecondarymineralsminerals mineralsminerals
Transformations
Smectite Soil
NE Montana VertisolHawaiian Oxisol
Iron and Al-oxide Rich
4.38
?
Young, weakly weathered soils= fine-grained mica, chlorite, vermiculite
(Entisol, Inceptisol)
Intermediate weathering= vermiculite, smectite, kaolinite
(Mollisol, Alfisol, Ultisol)
Strong weathering= kaolinite, hydrous oxides
(Ultisol--> Oxisol)
Mineralogy reflects weathering processes
Weathering of Parent MaterialWeathering of Parent Material
PhysicalPhysical–– Thermal expansion/contractionThermal expansion/contraction
Freeze/thawFreeze/thaw–– Erosion (water, ice, wind)Erosion (water, ice, wind)–– Biological (plant roots…)Biological (plant roots…)
Weathering of Parent MaterialWeathering of Parent MaterialChemical Chemical –– HydrationHydration–– HydrolysisHydrolysis–– Acidic DecompositionAcidic Decomposition
Water, inorganic and organic acidsWater, inorganic and organic acids
–– Complexation Complexation DecompositionDecompositionOrganic acidsOrganic acids
–– Reductive/oxidative dissolutionReductive/oxidative dissolution
Flood Plain (First Terrace)Boise Valley
Alluvial Deposits
Gains
Organic Matter4.40
- reactive functional groups: carboxyl, hydroxyl, phenolic
* Humus, Humic Acid, Fulvic Acid
Volcanic ashover alluvium
Bonner Series
Losses
-Erosion-Leaching