NRES 201 1nd Edition Exam 3 Study Guide Lectures Cumulative NRES 201 Final Exam Study Guide Soil 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 Layer B Subsoil C Parent Material not yet soil Regolith O A B C Soil Components Living Organisms Biomass Organismal Remains Residue Decay Products Humus Pedosphere 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 Hue Clay Smallest so it has the highest surface area per unit weight Texture When forming a ribbon Plasticity Clay Content Grittiness Soil Content Types 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 break 3 Spheroidal Granular Crumb Prominent in surface soils under grasslands where earthworms have been active 4 Plate Like Horizontal peds plates Surface and subsurface horizons 5 Block Like Found in B horizons good for drainage 6 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 Agents 3 Additions From external sources 4 Losses To the external environment Igneous From molten magma below Earth s crust Sedimentary From igneous rocks Dominant type of rock Metamorphic Combination of Igneous and Sedimentary 2 Most Common Elements Oxygen and Silicon Residuum Derived from rock that weathers in place Form on the summit Colluvium Material is deposited at the base of steep slopes Form on the slopes Alluvium Deposited by flowing water From in the valley most fertile Alluvial 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 Deposits Marine Sediments A coastal plain gradually accumulates Glacial 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 movement Glacial 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 gravel Eolian Deposits Transported by Wind 4 Types 1 Dune Sand 2 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 much lower quantities than loess 4 Volcanic Ash Organic 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 level Illuviation Gain by a lower level Higher 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 Soils There is a greater soil acidity under coniferous than deciduous trees Trees Thicker O Horizon Soil 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 regions Weathering Physical Process Disintegration by Temperature o 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 Hydration o Chemical bonding of intact water molecules to minerals High mineral size Low Stability Hydrolysis o MOST important chemical weathering process o Involves Dissociation of water and mineral decomposition by ion replacement Dissolution o Cations and Anions are surrounded and isolated They lose their attraction for each other and the mineral dissolves Oxidation Reduction o 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 C Layers 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 horizon that is high in organic matter Histic Formed in wet areas Subsurface Horizons Albic Light colored eluvial E horizon depleted of clay Argillic Illuvial Bt clay accumulation most common in IL Natric Illucial Btn horizon with clay High pH Cambic May show carbo depletion Kandic Occurs below an abrupt boundary Oxic High in clay Found in humid and subtropical regions Spodic Found