MIDTERM 1 Flashcards
What is soil?
unconsolidated geologic or organic material of at least 10cm in depth – 3D body –
Affected by soil forming factors/processes and are capable of supporting plant growth
What are the 3 phases of soil?
water (liquid), air and solids (organic and mineral)
What is soil composed of (%)?
About half pore space (20-30% air and 20-30% H20) and half soil solids (45% mineral/geological and 5% organic)
What are the 2 basic concepts of soil?
edaphology and pedology
What is edaphology?
the study of soils as a medium for plant growth
What is pedology?
the study of soils in relation to their environment
What kinda science is soil science?
applied science
What is porosity?
gives soil the ability to carry nutrients and minerals – also known as where “things” live
What are the differences between soil and rocks?
soil is/has porosity, organic matter and is unconsolidated
What are the 4 components that make up pedology?
atmosphere, biosphere, lithosphere and hydrosphere
What are pedons?
the smallest volume (3D) that can be regarded as a “soil” – basic unit of soil (each have different cell forming factors)
What are polypedons?
a contiguous group of similar pedons (used for mapping)
What is a profile and what is one composed of?
a vertical slice through the soil (2D) – normally 1-100 cm and containing A, B and C horizons
A: surface
B: subsurface
C: parent material
What are the 3 major integrated steps of soil formation?
- Accumulation of parent material – geologic mat on soil: due to wind, H20 and ice
- Effect of soil forming factors at larger scales
- Differentiation of horizons within the soil profile by soil forming processes
What are horizon differentiations characterized as?
additions (aka inputs/illuviations), loses (aka exits/eluviations), transfers/translocations (movement of soil constituents within the profile and/or between horizons) and transformations (chemical weathering or of coarse OgM into decay resistant organic compounds)
How long has soil been developping in Canada?
15,000 years
How does the mode of transport/deposition affect soil parent materials?
alters texture and provides some common patterns of surface expression in the landscape
What are the 2 types of soil parent materials?
Organic (from wetlands) vs mineral (transported or weathered bedrock)
Where do soil parent materials come from?
Residual vs transported (formed in place vs moved by wind, H20 or ice)
What are the 2 types of transported soil parent materials?
sorted (homogeneous particle size): low E deposition
unsorted (heterogeneous particle size): high E deposition
What does alluvial mean? (modes of deposition of transported soil PM)
(moving water): high/low E — round rocks, sorted, fine texture
What does marine mean? (modes of deposition of transported soil PM)
(tides): low to high E
What does lacustrine mean? (modes of deposition of transported soil PM)
(standing water): low E – very fine texture, sorted, varves
What does eolian mean? (modes of deposition of transported soil PM)
(wind): low E — sorted
What does glacial ice mean? (modes of deposition of transported soil PM)
(moraines/till): high E – unsorted, subangular (not perfectly round)
What does colluvial mean? (modes of deposition of transported soil PM)
(gravity): high E – unsorted, very angular
What are the 3 phases of horizontal soil morphology?
A: eluviation
B: illuviation
C: parent material
What are the 4 key soil characteristics?
Color: due to REDOXomorphic conditions and OgM additions
Texture: due to clay movement and nutrient/H2O retention
Structure: due to sodium content, clay loss/addition and OgM additions
Presence of carbonates: can help determine where horizons begin/end and tells about PM geology
What are REDOXomorphic conditions due to and what colours do they turn?
due to iron
Oxidized = orange
Less iron = blue/gray
What are mottles?
patches of orange on blue/gray background due to moisture content that’s affected by seasonal saturation and/or extreme precipitation
What are the 3 components of soil colour?
Hue: spectral color
Value: the darkness (affected by OgM)
Chroma: intensity
What are the textures of soil particles (order)?
Soil = > or = 2mm
Rock = >2mm
Sand = 2-0.02mm
Silt = 0.02-0.002mm
Clay = < or = 0.002mm (2um)
What are soils primary particles?
sand, silt and clay particles
What is granular soil structure?
resembles cookie crumbs and is usually less than 0.5cm in diameter – found on surface horizons where roots have been growing (A - OgM addition)
What is blocky soil structure?
irregular blocks that are usually 1.5-5m in diameter (B - clay addition)
What is prismatic soil structure?
vertical columns of soil that might be a number of cm long – usually found in lower horizons (B - Na addition)
What is columnar soil structure?
vertical columns of soil that have a salt cap at the top – found in soils of arid climates (B - sodium addition)
What is platy soil structure?
thin, flat plates of soil that lie horizontally – usually found in compacted soil (A - clay loss)
What is single grained soil structure?
soil is broken into individual particles that do not stick together – always accompanies a loose consistence and is found in sandy soils (coarse texture - absence of glue)
What is hue?
dominant spectral colour (most mineral soils found to be somewhere between red-yellow)
Redox soils normally a blue-green colour
What is value?
degree of darkness (black = 0 to white = 10)
What is chroma?
the intensity of colour (0 = pastels to 10 = bright)
Where is hue and redox on the munsell wheel?
normally hue is 5R-5Y whereas redox is around 5B-5BG
What colour does oxidizes/gleyed iron yield?
Oxidized Fe3+ = bright red (= good drainage)
Reduced Fe2+ = gleyed colour (= poor drainage)
How does moisture/OgM affect value?
Increased moisture content = decreased value (gets darker)
Increased OgM content = decreased value (gets darker)
Lighter colour = ____ value?
Lighter = increased value
Light brown = value >6 with 1-3% OgM
Brown = value 4-5 with 3-5% OgM
Black = value <3 with >5% OgM
What are carbonates?
white mottles not associated with REDOX conditions
What is loam?
equal distribution of all particles (sand, silt and clay)
How does drainage affect colour?
If in drainage area, normally blue/gray due to REDOX conditions
What is clay?
Soil particle size =or<0.002mm
Kind of mineral (ilite, smectite, montmorillonite)
Textural class (>40% clay content)
Derived from PM
Clay is an important physical and chemical property due to high SA (makes soil sticky)
Eluviation vs illuviation of clay
Eluviation: lessivage = loss of clay
Illuviation: accumulation, leads to clay skins
What is a key characteristic of lacustrine freshwater lakes?
Have varves (inherited property) from PM deposition
Seasonal differences in water movement can influence particle deposition
What are the downsides to sand/silt and clay?
sand/silt = susceptible to erosion // clay = susceptible to compaction
What is structure?
Combo of primary particles (sand, silt and clay) into secondary structural units (peds or aggregates)
What are the 4 kinds of structure?
structure less, block-like, plate like and prism like
What is class?
size of aggregates (fine, medium and coarse)
What is grade?
can we see peds in the profile (weak, moderate or strong)
What is consistence?
stability of ped outside profile
Friable, loose or firm
Stickiness (when wet)
strength/resistance to deformation
What are the 4 types of glue?
- Glue = clay (sticky)
drying/wetting cycles cause shrink/swell
Bt horizon: lessivage, slay skins (blocky) - Glue = OgM
Ah horizon: high biological activity (root microbes) – granular - No glue = Clay + Na+
Bnt horizon: dispersion of clay on top, deposition of salt, water erosion on sides (columnar) - No glue = none left
Ae horizon: loss of clay, thin horizontal peds (platy)
How do structural units develop?
Adhesive substances (glue)
Forces (copaction, swelling-wetting or freezing, bioturbation, etc.)
Genesis of texture and structure?
Texture: property inherited from the soil PM
Structure: forms in response to pedogenic processes
Soil structure = 2D
Soil texture = not inherited nor glued together, 1D particle
What is the influence of structure on soil performance?
Decrease: susceptibility to erosion and compaction
Increase: aeration, drainage, root growth (porosity) and microbial activity
What factors control processes and form soils?
Climate
Organisms
Parent material
Relief
Time
Factors affect what processes that form soils?
Additions: OgM, clay, iron oxides, salts
Loses: OgM, clay, iron oxides, salts
Translocation: OgM, clay
Transformations: OgM, minerals
What soils are formed from factors and processes?
Horizons
Colour
Texture
Structure
Carbonates
Biota
Mineralogy
Biogeochemistry