NRES 201 1nd EditionExam # 3 Study Guide Lectures: CumulativeNRES 201 Final Exam Study GuideSoil is the upper part of Earth's crust and is formed by 5 soil forming factors: Climate, Organisms, Topography, Parent Material, and Time. Solum (true soil) has three horizons O = Organic P = Plow LayerB = SubsoilC = Parent Material - not yet soilRegolith = (O + A + B + C)Soil Components - - Living Organisms = Biomass- Organismal Remains = Residue- Decay Products = HumusPedosphere = Soil. The outermost layer of the Earth, where soil forms and life begins.Soil Color - - Hue = Dominant Spectral Color- Value = Lightness/ Darkness- Chroma = Intensity/ Brightness of the HueClay = Smallest so it has the highest surface area per unit weight. Texture - When forming a ribbon: Plasticity = Clay Content, Grittiness = Soil ContentTypes of Soil Structure: ( Grade = Distinctness of peds - strong/weak, Class = Size)1. Structureless: Single grained (loose sand/ dust)2. Massive: Very large clods - difficult to break3. Spheroidal: Granular/ Crumb, Prominent in surface soils under grasslands - where earthworms have been active. 4. Plate - Like: Horizontal peds/ plates, Surface and subsurface horizons5. Block - Like: Found in B horizons - good for drainage6. Prism - Like: Found in B - horizons - common in arid/ semiarid 4 Soil Forming Processes - 1. Transformation - Chemical/Physical Changes. (Destruction or Synthesis)2. Translocation - Movement with or between horizons. Water = Transporting Agents3. Additions - From external sources4. Losses - To the external environmentIgneous = From molten magma below Earth's crustSedimentary = From igneous rocks (Dominant type of rock)Metamorphic = Combination of Igneous and Sedimentary2 Most Common Elements = Oxygen and SiliconResiduum - Derived from rock that weathers in place. - Form on the summitColluvium - Material is deposited at the base of steep slopes- Form on the slopesAlluvium - Deposited by flowing water- From in the valley - most fertileAlluvial Fans - Formed by a sudden descent in stream flow that deposits sediments at the base of the slope.Delta - Formed at the mouth of some rivers, as sediments deposit from slow - moving water.Freshwater Lakes - Lacustrine DepositsMarine Sediments - A coastal plain gradually accumulatesGlacial Till - Materials deposited directly by ice. It is Heterogeneous. - End Moraine - Till placed at a terminal or recessional edge of the glacier- Ground Moraine - Level till plain formed beneath the glacier- Drumlin - Large, elongated hill oriented with the direction of ice movementGlacial Outwash - Materials carried by torrents of melt-water. Free drainage formed an outwash plain.- Kame - Isolated mound of sand and gravel- Kettle - Closed depression- Esker - Long, winding ridge of sand and gravelEolian Deposits - Transported by Wind. 4 Types:1. Dune Sand2. Loess - Silt sized materials deposited by wind. Predominant parent material for Illinois soils. 3. Aerosolic Dust - Very fine particles carried high into the air. Usually deposited by rainfall, in muchlower quantities than loess. 4. Volcanic AshOrganic Deposits accumulate in marshes and swamps. They may be mixed with inorganic material.2 types:1. Peat (un-decomposed) 2. Muck (partially decomposed)Eluviation - Loss from an upper levelIlluviation - Gain by a lower levelHigher temperatures greatly increase regolith weathering and are much more effective in promoting soil formation in humid climates than arid climates. - Plant roots alter the parent material by - Attacking minerals, Generating acidity, Mobilizing nutrients, Stimulating microbial activity - Plant shoots initiate surface stratification by - Litter deposition, Nutrient enrichment, Building granular structure and Enhancing water infiltration. There is a higher organic matter content under grass than forest- Grass = Dark Prairie Soils- Trees = Light Forest SoilsThere is a greater soil acidity under coniferous than deciduous trees - Trees = Thicker O HorizonSoil formation is more rapid for north facing slopes. There is more sunlight exposure to south facing slopes. Poor developed soils - Arid regions, Well developed soils - Tropical regionsWeathering Physical Process - - Disintegration by Temperatureo Differential Expansion: When heated, some minerals expand more than others. o Exfoliation: Rocks heat/ cool more quickly on the outside than the inside - causes outer layer to peel away. Weather Chemical Process - - Hydrationo Chemical bonding of intact water molecules to minerals. ( High mineral size = Low Stability)- Hydrolysiso MOST important chemical weathering process.o Involves: Dissociation of water and mineral decomposition by ion replacement. - Dissolutiono Cations and Anions are surrounded and isolated. They lose their attraction for each other and the mineral dissolves.- Oxidation - Reductiono Addition of O2 causes oxidation (occurs by physical weathering)o Removal of O2 causes reduction (occur by waterlogging) - Complexation o Metal ions form complexes with electron - rich compounds such as organic acids. It decreases reactivity and increases mobility. Soil Profile:- Surface Organic Layer = O- Mineral layer (developed by soil forming processes) = A, E, B- Underlying Parent Material = CLayers - - O = Composed of organic matter. Occurs in forests, not prairies. Cultivation destroys this layer.- A= Topmost mineral horizon. Dark colored by humus. Granular texture. Finer materials lost by eluviation and erosion.- E = Light colored and formed by eluviation. Common in forest, not prairie. - B = Illuvial horizon from clay accumulation in humid regions.- C = Unconsolidated material underlying the solum- R = Consolidated bedrock and no weathering.Major Subordinate Distinctions - - b = Buried Horizon- g = Strong gleying (mottling) - Due to Fe reduction/ oxidation- k = Accumulation of Carbonates - Common in arid regions- n = Accumulation of Sodium - Destroys soil structure. Problem in arid regions- p = Plowing - Occurs in A Horizon- t = Accumulation of Clay - Common in humid (forest soils)- w = Weakly developed B Horizon- x = Fragipan - Hard, dense loamy layer that restricts water flow and root penetration. It often occurs below the B horizon. Surface part of the Pedon = Epipedon- Mollic - Most common in Illinois. Formed under grass- Umbric - Forms in areas with higher rainfall. More acidic than mollic epipedon.- Ochric - Mineral horizon- Mellanic - Developed from volcanic ash. Not in Illinois. Thick, black mineral