SS-120 Midterm
Vasily Dokuchaev
Russian soil scientist
exfoliation
The peeling away of the outer layers from a rock
what is the particle density of most soils?
2.65 g/cm^3
Which moisture regime does Cal Poly SLO have?
Xeric
Block-like structure
cemented by clay; common in B horizons; angular blocky or sub angular blocky
transformations
change
how does chemical weathering occur?
chemical decomposition by water, organisms, & chemical rxns
"w" subhorizon
distinctive colour/structure w/o clay accumulation
preferential flow
saturated flow is a lot faster in clays when there are cracks
"g" subhorizon
strong gleying (reduced conditions)
peds or aggregates
structural units formed by particles bound together
subgroups
subdivisions of great groups
what are the 3 different types of rocks that comprise the Earth system?
igneous, sedimentary, metamorphic
size of clay, silt, sand, and gravel particles
-clay: <0.002 mm -silt: 0.002-0.05 mm -sand: 0.05-2 mm -gravel: >2 mm
micropores
- <0.08 mm -usually filled w/ water -intraped pores -can fit bacteria
macropores
- >0.08 mm -air exchange, H2O drainage -interped pores (cracks, spaces between peds) -biopores (root channels, worm burrows)
hans Jenny
-American soil scientist -wrote "factors of soil formation" -created equation of soil forming factors
Spodosols
-acid, sandy, forest soils, highly leached -subsurface accumulation of organic matter -occur under coniferous forests in cool, moist environments -~4% of global ice-free land area
percolation
-after infiltration, movement downward through soil profile -initial saturated flow near surface, then unsaturated flow as wetting front moves into underlying dry soil
ultisols
-argillic horizon, highly leached, acidic soils -primarily in humid temperate & tropical areas on older, stable landscapes -intense weathering of primary minerals w/ most of Ca, Mg, & K leaches from soil -~8% of global ice-free land area
alfisols
-argillic/natric horizon, moderately leached -moderately leached soils w/ a subsurface zone of clay & >35% base saturation -not developed enough to be a mollisol -~10% of global ice-free land area
matric potential
-attraction of water to solid soil surfaces (adhesion) -negative because water attracted to soil surface has lower energy state than pure water
taxonomy
-branch of science concerned w/ classification -language used to describe soils
topography (relief)
-configuration of land surface -differences in elevation, slope (% and shape), and landscape position -can speed up/slow down climate-driven soil forming processes by influencing water inputs -modifies balance between soil formation and soil destruction
intrusive rock
-cools inside of Earth's surface -medium/large crystals (slow cooling)
extrusive rock
-cools outside of Earth's surface -fine crystals (faster cooling)
mollisols
-dark, soft soils of grasslands -~7% of global ice-free land area
vertisols
-dark, swelling, & cracking clays -during dry periods, soil volume shrinks & deep, wide cracks form -soil volume expands when it gets wet -~2% of global ice-free land area
Particle density (D_p)
-density of mineral fraction of pie chart only -determined by chemical, crystal composition -not affected by particle size, pore space/size, management
organic soil
-derived from plants &/or organisms & biomass -must have >20% organic carbon by weight
mineral soil
-derived from rocks & minerals -<20% organic carbon by weight (typically 1-6%)
soil potential
-difference in energy level of water (e.g. between wet & dry soil) determines direction & rate of water movement in soils & plants -water moves from soil zone with high soil water potential to one with a lower soil water potential
biogeochemical weathering
-disintegration of minerals & rocks they make up by changes in chemical composition -incorporates biological (plants & animals), geological (minerals), & chemical (reactions) processes
O master horizon
-dominated by organic soil material -usually present at soil surface -sometimes buried by mineral soil (uncommon)
aridisols
-dry soils, limited leaching -characteristic of dry-desert regions -~12% of global ice-free land area
osmotic potential
-due to dissolved substances (salts) in water -increased salts=more negative osmotic potential
reduction
-element gains e- -occurs in high water saturation, low oxygen conditions
oxidation
-element loses e- (OIL RIG) -When minerals react w/ oxygen, their chemical composition changes & they're more susceptible to further weathering
Bulk density (D_b)
-entire pie chart -density of entire bulk soil, including pore spaces & organic matter -influenced by texture, pore space, compaction, organic matter, structure, & anything that affects volume -variable & dependent of texture & compaction
infiltration
-entry of free water into soil at soil-atmosphere interface -quick when water flows through macropores/clay cracks -slow when macropores fill & cracks close up
saturated
-every pore is filled w/ water -gravity plays most imp. role -soil potential energy= 0 kPa
inceptisols
-few diagnostic features: inception of B horizon -soils that exhibit minimal horizon development -lack features that are characteristic of other soil orders -~15% of global ice-free land area
igneous rocks
-formed directly from cooling of molten magma -composed of randomly interlocked primary minerals
metamorphic rocks
-formed from igneous & sedimentary rocks under extreme heat & pressure due to shifts in continental plates
sedimentary rocks
-formed from sediment that came from weathering of different rocks -most common rock type (75% of Earth's land surface)
gravitational potential
-gravity acts on soil water same as on anything else -differences are always positive because reference elevation of pure water is purposefully designated at a site below that of soil water
"a" subhorizon
-highly decomposed organic matter -part of O horizon
climate
-how atmosphere behaves over a long period of time & space -2 main components are precipitation & temperature
"e" subhorizon
-immediately decomposed organic matter -part of O horizon
oven dry
-lab measurement (105 degrees C for 24 hrs) -soil potential energy= -1,000,000 kPa
osmosis
-liquid water moving in response to differences in osmotic potential -only occurs if a semipermeable membrane exists (e.g. plant cell)
unsaturated flow
-macropores are filled w/ air -only micropores have water -gravitational potential has no effect, only matric potential -anytime when moisture potential is <0
B master horizon
-mineral horizon formed below O, A, &/or E horizons -parent material significantly altered by accumulation & alteration
A master horizon
-mineral horizon typically at soil surface &/or under O horizon -decomposed organic matter mixed w/ mineral soil -shows evidence of destruction of much or all of original rock structure -mostly mineral material, but has evidence of organic matter decomposition & accumulation by darker colour
E master horizon
-mineral horizon w/ evidence of loss of organic matter -results in concentration of sand & silt particles of quartz & other resistant minerals -lighter in colour than A & B horizons -may be directly under O horizon -underlain by B horizon
C master horizon
-mineral horizon w/ little or no alteration by soil forming processes -lack properties of all other master horizons -parent material
permanent wilting point
-moisture content of soil at which plants fail to recover their turgidity -soil potential energy=-1,500 kPa
Oxisols
-most highly weathered -oxic horizons: high degree of weathering of minerals; iron & aluminum oxides accumulate -contain few weatherable minerals & are often rich in Fe & Al oxide minerals -typically found in tropical regions -characteristic red colour -~8% of global ice-free land area
Pedoturbation
-movement/mixing of soil through profile -process of both translocations & additions
bioturbation
-movement/mixing of soil through profile aided by organisms -process of both translocations & additions
Histosols
-organic soils w/o permafrost -characteristic of wetlands -contain at least 20-30% organic matter by weight & are more than 40 cm thick -bulk density is typically less than 0.3 g/cm^3 -store disproportionately high amnt of soil carbon relative to their distribution -cover ~1% of global ice-free land area
entisols
-recent (little if any profile development) -all soils that don't fit into any other order -many found on steep, rocky slopes -18% of global ice-free land area
water movement of sand, silt, & clay
-sand: fast -silt: medium -clay: slow
feel of sand, silt, & clay
-sand: gritty -silt: smooth -clay: sticky
pollutant leaching potential of sand, silt, & clay
-sand: high -silt: moderate -clay: low
chemical reactivity of sand, silt, & clay
-sand: low -silt: low -clay: high
influence of sand, silt, & clay on whole soil
-sand: low -silt: low -clay: high
nutrient holding capacity of sand, silt, & clay
-sand: low -silt: low -clay: high
pore space of sand, silt, & clay
-sand: low -silt: low -clay: high
water holding capacity of sand, silt, & clay
-sand: low -silt: medium -clay: high
surface area of sand, silt, & clay
-sand: low SSA -silt: low SSA -clay: high SSA
pore size of sand, silt, & clay
-sand: macropores -silt: mesopores -clay: micropores
mineral type of sand, silt, & clay
-sand: primary -silt: primary -clay: secondary
i subhorizon
-slightly decomposed organic matter -part of O horizon
saturated flow
-soil potential energy = 0 -when every pore is filled w/ water -matric potential has no effect, only gravitational potential
Gelisols
-soils that have permafrost & frost churning -located in cold regions, so decomposition is surpressed -found at higher latitudes -cover ~9% of global ice-free land area
suborders
-subdivision of soil orders -properties that reflect major environmental conditions or soil forming processes -many are based on soil moisture regime
great groups
-subdivisions of suborders -driven by diagnostic subsurface horizons
aspect
-the direction a slope faces -modifies local environmental conditions
Andisols
-volcanic ash soils -most rare -dominated by glass & short-range-order weathering products (allophone, impolite, ferrihydrite) -high water holding capacity -~1% of global ice-free land area
bioweathering
-weathering of rocks & minerals due to production of inorganic acids, organic acids, & chelates by bacteria & fungi
field capacity
-when all gravitational water is drained from soil -gravitational forces become negligible & matric forces play a greater role -soil potential energy= -33 kPa
biological soil crusts
-when all kinds of organisms come together to create a mat of soil crusts -makes soil less susceptible to soil erosion -increases water infiltration -cyanobacteria fix nitrogen from atmosphere & bring it into soil
Soil water is considered plant unavailable between:
0 kPa and -33 kPa & -1500 kPa and -1,000,000 kPa
hierarchy of weathering resistance (most resistant to least resistant)
1. Gothite 2. hematite 3. gibbsite 4. clay minerals 5. dolomite 6. calcite 7. gypsum
what are the 3 main components of the munsell colour system?
1. Hue- spectral colour 2. Value- light/dark 3. Chroma- saturation Format: Hue Value/Chroma
Structure of U.S. Soil Taxonomy
1. Order (12) 2. Suborder (68) 3. Great group (444) 4. Subgroup (~2,500) 5. Family (~8,000) 6. Series (~25,000)
soil moisture regimes
1. aquic- saturated w/ water 2. udic- sufficiently high soil moisture year round 3. ustic- intermediate soil moisture 4. aridic- dry for at least half growing season 5. xeric- mediterranean climate, cool & moist winters, dry & warm summers
what factors influence soil colour?
1. organic matter content 2. water content 3. oxidation state
types of weathering
1. physical- disintegration 2. chemical- decomposition 3. biological- disintegration &/or decomposition
what do soil organisms alter?
1. soil structure 2. infiltration & water dynamics 3. availability of nutrients 4. decomposition of organic matter 5. movement of organic matter 6. habitat for other soil organisms 7. microbial community growth & activity 8. plant growth and productivity
Which chemical reaction is an example of oxidation and is responsible for the formation of rust on some minerals?
4FeO + O2-> 2Fe2O3
Which soil is most likely to be the most weathered and have the greatest degree of soil formation?
A deep soil with lots of clay, a low pH and strong differences between horizons
A soil horizon is full of plant roots and is darkened with organic matter. What soil horizon is it?
A horizon
The subordinate designation "p" for the affects of plowing can only be associated with what master horizon?
A horizon
Which master horizon would you expect to find granular structure?
A horizon
Two soil samples, A & B, at different soil moisture levels are placed in contact with each other. Water will more likely move from soil A to soil B if their water potentials, expressed in kPa, are:
A=-30; B=-40
Permeability
Ability of rock or soil to allow water to flow through it
Which soil order is developed from volcanic ash and is dominated by amorphous minerals like allophane and imoglite?
Andisols
what mineral is an important source of phosphorus?
Apatite
What soil order is classified based on climatic conditions?
Aridisols
Why should we care about soils?
Because soils provide ecosystem services without which life as we know it wouldn't exist
Which chemical process is responsible for producing acid and is generally most important in soil surface horizons?
CO2+ H2O ->H2CO3
The tendency of water to move against gravitational forces into small pores due to surface tension is called:
Capillarity
granular structure
Commonly found in A horizons
How does compaction affect soil texture?
Compaction doesn't affect soil texture
Which diagnostic subsurface horizon resists water and root penetration?
Duripan
Dirt is just another name for soil
False
The C horizons are generally more completely weathered than the other horizons.
False
Parent materials from weathered basalt result in
Fine-textured soils containing Ca, Mg, and Fe
What equation represents hydrolysis?
KAlSI3O8+ H2O -> HAlSi3O8 + K+ + OH-
Where does the raw material from which soils form originally come from?
Most soils are mineral soils, so they're derived from the lithosphere
Alfred H Munsell
Munsell colour system adopted by USDA as official colour system for soil research in 1930s
Which horizon is most likely to be found under forested vegetation but not under grassland vegetation?
O horizon
master horizons
O, A, E, B, C, R
What are the most common elements in Earth's crust?
Oxygen and silicon
Which soil should you pour your beverage on to quickly dispose of the evidence?
Soil A has a Ksat of 0.01 cm/sec
The Ludden series in North Dakota is classified as this: frigid Typic Endoaquerts What soil order is it?
Vertisol
If you wanted to find a soil where physical weathering dominated over chemical breakdown you would be most apt to find it in ______.
a desert region of Arizona
Chronosequence
a set of soils that share a common climate, parent material, slope, & community of organisms, but differ w/ regard to length of time they have been subject to weathering of soil formation
ponded water (hydraulic head)
above soil surface; standard reference point
"y" subhorizon
accumulation of gypsum
"k" subhorizon
accumulation of organic matter
"t" subhorizon
accumulation of silicate clays
acid reactions
acids react w/ minerals resulting in weathering
What physical, chemical, & biological processes are soils governed by?
additions, translocations, transformations, & losses
what are the soil forming processes?
additions/inputs --> losses/outputs --> translocations --> transformations
what does grey coloured soil mean?
aerobic/water-logged conditions
At what condition would you expect the highest soil oxygen content?
air dry
Hydrogen bonding
allows water to weakly bond to itself (cohesion) & other surfaces, like soil particles (adhesion)
density
amount of mass that fits in 1 volume
darcy's law
amount of water flowing through soil depends on energy driving water flow/hydraulic head, hydraulic conductivity of soil, & area through which water is flowing
surface tension
at liquid-air interface, surface tension results from greater attraction of water molecules from each other than for air
Which soil profile is the shallowest?
backslope because more erosion occurs here, gravity & water translocate material, and less soil accumulates here
R master horizon
bedrock
weathering
biochemical process by which rocks & minerals are broken down into finer fragments & new minerals can be synthesized in process
What in the fine earth fraction of soil determines the length of a ribbon when doing the texture by feel method?
clay
what soil texture holds the most water?
clays because of micropores
what kind of climate does wind erosion & physical weathering dominate?
cold & dry environment
Hypergelic
coldest temperature regime
The mixed angular gravel, rock, and soil found at the foot of a hill slope is typical of what type of parent material?
colluvium
prism-like structure
common in B horizons & in soils of arid & semi-arid regions
plate-like structure
common in E horizons/compacted A horizons
weather
conditions of atmosphere over short period of time
lacustrine
deposited in lakes
gravimetric method
direct measurement of % soil water by mass (theta_m)
biopores
earthworm burrows & root channels
Pedosphere
environmental interface where atmosphere, biosphere, hydrosphere, & lithosphere come together to form soil
What is not part of the relief/topography portion of the soil forming factors?
erosion
hydrometer
extremely accurate instrument for determining soil texture
krotovinas
filled in animal burrows
The total soil water potential (YT) of a single soil profile is > 0 (or positive) only when all the soil pores are ___________ of water and there is a/n ____________ of water on the soil surface.
full; hydraulic head (ponded water)
parent material
geologic/organic precursors to soil
What mineral is the most resistant to weathering?
goethite
what is the best structure for growing crops?
granular
clay soil
greater total pore volume = greater porosity
toposequence
group of soils that occur on a landscape in which differences among soils occur from influence of topography
primary minerals
haven't been altered chemically since they formed as molten lava solidified
wet and warm climate
high weathering rates, high rates of biological decomposition, & high plant growth
what kind of climate does chemical weathering dominate?
hot & wet environment (because water is important component of chemical rxns & chemical rxns happen faster at warmer temps)
hyperthermic
hottest temperature regime
adhesion
hydrogen atoms are also bound to solid surfaces
cohesion
hydrogen atoms from one water molecule are attracted to oxygen of neighbouring water molecule (polymerization of water)
additions
inputs
hydration
intact water molecules bind w/ a mineral leading to different mineral products
what does red coloured soil mean?
iron oxides, tropical, old soil
soil
layers of generally loose mineral &/or organic material that are affected by physical, chemical, &/or biological processes at or near planetary surface and usually hold liquids, gases, & biota & support plants
what's the role of vegetation in soil organic matter formation?
leaf litter, root litter, and root exudates are precursors to soil organic matter
sandy soil
less total pore volume = less porosity
dry and cold climate
limits chemical weathering, limits microbial activity & decomposition, can limit plant growth
What does a high porosity mean for bulk density?
low bulk density
What will most affect the flow of water in unsaturated soil?
matric potential
topography
mean annual precipitation is same at each landscape position
seasonal distribution
mean annual precipitation is same in both systems, but varies by season
cryoturbation
mixing/churning of soils based on freeze --> thaw processes
water movement of blocky & prismatic structures
moderate water movement
alluvium
moved by flowing water
colluvium
moved by gravity
eolian (sand) or loess (silt)
moved by wind
translocations
movement
What mineral is not a secondary mineral?
muscovite
How is water polar?
one side is positive and the other is negative
what does very dark coloured soil mean?
organic matter accumulation
losses
outputs
how does physical weathering occur?
physical disintegration by temperature, water, ice, wind, organisms
what organisms influence soil?
plants, microbes, animals, & humans
what structure restricts/slows water movement
plate-like
"p" subhorizon
plowing
The water molecule's attraction for itself and charged solid surfaces results from its
polarity
Which soil properties affect saturated hydraulic conductivity (Ksat)?
porosity, soil structure, soil texture, and biopores
water movement of single grain & granular structures
rapid water movement
secondary minerals
recrystallized products of chemical breakdown and/or alteration of primary minerals
Gleying
reducing conditions in soil profile when water has saturated up through profile, reduction rxns occur, & result in blue/grey colour
soil texture
relative proportion of mineral particles (sand, silt, clay)
what does very light coloured soil mean?
salts, elluviation, low fertility
Which particle will fall out of suspension first when determining the soil texture by hydrometer method?
sand
what kinds of soil textures have more macropores?
sands & granulated clays
what soil textures hold the most PAW?
silt loams
what factor controls the amount of water being held?
size of pores
"ss" subhorizon
slickensides
water movement of platy & massive structures
slow water movement
Ponded water
soil potential energy= +
equation of soil forming factors
soil= f (cl, o, r, p, t...) "soil is a function of climate, organisms, relief, parent material, & time)
critical zone
soils and different spheres it interacts with
How do soils regulate water supplies?
soils control quantity & quality of water available to freshwater ecosystems
structure of soil
spatial arrangement of individual mineral particles to complex aggregations, peds, shapes
What soil profiles are the deepest?
summit & toe slope because at toeslope, all material that's moving down slope is deposited at bottom of hill. summit can also have deep soil profiles that are forming in residuum (weathering in place)
subhorizon distinctions
t, k, ss, b
Capillarity
the attraction between molecules that results in the rise of a liquid in small tubes (adhesion + cohesion)
How are soils a habitat for soil organisms?
they are home to lots of biodiversity
How do soils modify the atmosphere?
they're responsible for a large flux of CO2 (soil respiration) and other greenhouses gases (CH4, N2O) to atmosphere
flocculation
things that move and clump together
How do soils recycle raw materials?
through decomposition
Soil profile
unit for studying soil formation
hydrolysis
water molecules split into hydrogen (H+) & hydroxyl (OH-) components & hydrogen often replaces a cation from mineral structure
vapor movement
water vapor moves in response to differences in vapor pressure
residuum
weathered in place
paralithic contact/ residuum
weathering & decomposing rock