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