NRES 201 Lectures 4-6 (Fall 2014): Soil Formation11NRES 201Soil Formation2Today’s lecture topics- Nature of soil genesis- Rocks, the basic ingredient of soils - Parent materials- Residuum- Colluvium- Alluvium- Marine sedimentsSoil FormationNRES 201 Lectures 4-6 (Fall 2014): Soil Formation23Nature of soil genesisHow soils form- Soils form naturally at theEarth’s surface- At the interface betweengeological materials andthe atmosphere- Soils form gradually over time- Through the weathering ofparent material by climate and organisms interactingwith topography- The parent material comesfrom rocksSource: Nardi (2007)4The four soil-forming processes- Transformations- Chemical or physicalchanges in soil constituents- Destruction or synthesis- Translocations- Movement of materialswithin or between horizons- Water is the transportingagentSource: Brady and Weil (2010)NRES 201 Lectures 4-6 (Fall 2014): Soil Formation35- Additions- From external sources- Examples include:• Fallen plant leaves• Sloughed-off roots- Losses- To the external environment- Examples include:• Leaching to groundwater• ErosionSource: Brady and Weil (2010)6Rocks, the basic ingredient of soilsIgneous rocks- Originate from molten magmabelow the Earth’s crust- Form by the cooling ofvolcanic lava- Often contain interlockingmineral grains- Common examples:-Granite- Basalt-DioriteSource: http://www.huffingtonpost.comNRES 201 Lectures 4-6 (Fall 2014): Soil Formation47Sedimentary rocks- Formed from igneous rocks- Sediments settle under water and recement- The dominant type of rock- Common examples:- Sandstone- Limestone-ShaleSource: http://geology.comSandstone8Metamorphic rocks- Formed from igneous or sedimentary rocks under extreme temperature and pressure- Endless variety- Common examples:-Marble-Quartzite- SlateSource: http://geology.comMarbleNRES 201 Lectures 4-6 (Fall 2014): Soil Formation59Summary tableSource: Singer and Munns (1987)10Mineralogical composition- Minerals occur in rocks as solid crystalline substances- Primary minerals in igneous rocks- Secondary minerals in sedimentary andmetamorphic rocks- Formed by the weathering of primary minerals- Major mineral groups:- Silicates- Aluminosilicates- Metal oxides/hydroxides- Carbonates- Sulfides - SulfatesNRES 201 Lectures 4-6 (Fall 2014): Soil Formation611Elemental composition- Oxygen and silicon are the most common elements- Because silicate minerals make up more than90% of the Earth’s crust12Parent materialsFormed by weathering- Rocks disintegrated by:- Temperature changes- Erosive action of water,ice, and wind- Plants and animals- Rocks decomposed by:-Hydrolysis- Hydration- Carbonation- Oxidation- DissolutionIn 1944In 2002Source: http://www.whatischemistry.unina.itNote the change after this marble statue had weathered for 58 years.NRES 201 Lectures 4-6 (Fall 2014): Soil Formation713Potential for transport- Inorganic parent materials do not necessarily form in place- They may be transported from one site and deposited at another - Possible transporting agents:- Gravity- Flowing water- Glaciers-Wind- Transport often leads to sorting by size14Importance to soil properties- Texture- Coarse texture from sandstone- Fine texture from shale- Affects drainage and aeration- Soil reaction- Alkalinity from limestone- Acidity from sulfide-rich shale- Affects natural vegetation and chemical weatheringNRES 201 Lectures 4-6 (Fall 2014): Soil Formation815- Mineral composition- Affects clay mineralogy and land use- Also affects soil fertility- Soils are more fertile when there is a high content of minerals that supply:• Calcium (Ca)• Magnesium (Mg)• Potassium (K)- Over eons of time, soil fertility declines as these minerals are depleted by weathering- Native vegetation shifts toward species having low fertility requirements 16Residuum- Derived from rock thatweathers in place- No transporting agent- Often the parent materialfor older soilsSource: http://www.nrcs.usda.govNRES 201 Lectures 4-6 (Fall 2014): Soil Formation917- Prominent in mountainous and upland regions ofthe USA, the Great Plains, and the PiedmontSource: Brady and Weil (2008)Residuum prominent in green-shaded regions18Colluvium- Material moved by gravityand deposited at the baseof steep (talus) slopes- Unstable, prone tolandslides- Usually very coarsetextured and well drained- Highly variable incompositionSource: http://soilweb.landfood.ubc.caNRES 201 Lectures 4-6 (Fall 2014): Soil Formation1019- Colluvial soils arepoorly developed, andoften lack horizonsSource: http://www.pinterest.com20Alluvium- Material deposited byflowing water- Deposition can occur in:- Floodplains• Which becometerraces if the streamchanges grade• Coarser sedimentssettle near the streamchannelSource: Brady and Weil (2010)NRES 201 Lectures 4-6 (Fall 2014): Soil Formation1121• Floodplain soils are: Nearly level Highly fertileSource: http://webspace.ship.edumMissouri River floodplain, eastern Missouri22• Floodplain soils are: Nearly level Highly fertile Often stratifiedSource: http://jscnwy.wordpress.com/icelandNRES 201 Lectures 4-6 (Fall 2014): Soil Formation1223- Deposition can occur in:- Alluvial fans• Formed by a sudden descent in stream flow that deposits sediment at the base of a slope• Sorted by size: Coarser particlesat the top Finer particles atthe bottom• Alluvial soils are: Often highlyfertile Prone to floodingSource: http://epod.usra.eduKenai Peninsula, Alaska24- Deposition can occur in:-Deltas• Formed at the mouth of some rivers, as sediments deposit from slow-moving water• An extension of thefloodplain• Delta soils are: Fine-textured Highly fertile Poorly drainedSource: http://en.wikipedia.orgNile River and Delta, EgyptNRES 201 Lectures 4-6 (Fall 2014): Soil Formation1325- Deposition can occur in:- Freshwater lakes• Analogous to delta formation• Known as lacustrine deposits• Size-sorted with: Sand and gravel atthe entrance point Silt and clay in mostof the lake• Lacustrine soils are: Layered Fine-textured Poorly drainedSource: http://soilweb.landfood.ubc.caLacustrine deposit in an old lakebed26Marine sediments- Gradual accumulation of sediments carried by stream flow into oceans, estuaries, and gulfs- A coastal plain builds up over time- Acidification occurs during soil formation- Coastal plain soils:- Vary widely in textureand productivity- Are more level nearthe coast than inlandSource: