Exam #1 Flashcards
what is soil made of?
45% minerals
25% air
25% water
5% organic matter
an average soil is composed of ____ pore space found between particles
50%
what are the five plant growth factors?
light, temperature, water, nutrients, and genetics
define “soil”
the material; mixture of minerals, gases, water, organic matter, and organisms capable of supporting plant life
define “a soil”
an individual natural body (organized, 3-dimensional, region/biome specific, and has distinct characteristics.
define “the soil”
all of the soils (natural bodies). soil the material, roots, ground dwelling animals and rocks.
the soil (all of the soils) is also called the ______
pedosphere
what are the four spheres of the pedosphere? (spheres are always intertwined)
1) atmosphere/soil air (CO2, O2 and N2)
2) biosphere/organic matter and biomass (plants, animals, microbes)
3) hydrosphere/soil water (water and dissolved substances)
4) lithosphere/soil particles (minerals in rocks, clay and sediments)
soils have layers called what?
horizons (O horizon, A horizon, B horizon, C horizon and bedrock)
how long does it take for 1 in of topsoil to form?
500-1000 years
soil quality is determined by its capacity to….
provide ecosystem services
what are ecosystem services?
products and functions of natural systems that support and fulfill the needs of humans
what are the six ecosystem services provided by soils?
1) plant medium growth (nutrients, physical support, root aeration, moisture supply and storage, temperature regulation, and protection from toxins)
2) provides and recycles nutrients (mineral weathering releases nutrients from unavailable storage forms)
3) regulates the atmosphere (huge carbon pool or sink)
4) provides hidden habitat (bacteria, fungi, insects, earthworms, etc)
5) serves as an engineering medium (building infrastructure)
6) nature’s rain barrel (storage) and water filter
is soil a renewable or a non-renewable resource?
non-renewable
what is soil degradation?
reduction is soil quality
what are the causes of soil degradation?
erosion, nutrient depletion, organic matter depletion, compaction, acidification, and salt accumulation
what percentage of soils have been degraded?
33% of global soils
soil restoration is key to _______
agroecosystem restoration
where does soil form?
Earth’s crust, upper lithosphere (and uppermost solid mantle)
what is the critical zone?
top of tree canopy to the water table
soil is the heart of the _______ _____
critical zone
Igneous rocks forms…
during cooling and crystallization of lava or magma
Sedimentary rocks forms…
from cementation (lithification) of sediments (small rock fragments)
Metamorphic rocks forms…
when igneous or sedimentary rocks are altered under high heat and pressure conditions found deep in Earth’s crust
what is the rock cycle? draw it
When igneous rocks are eroded by
wind, water or ice, and the resulting particles are deposited elsewhere and cemented, they become sedimentary rocks. Sedimentary and igneous rocks exposed to extreme heat and pressure become
metamorphic as their minerals re-crystalize. Metamorphic rocks can become sedimentary rocks in the same way as igneous rocks can. In reality, multiple kinds of igneous and/or metamorphic rocks can
combine to make sedimentary rocks.
Mafic vs. felsic minerals in Igneous rocks
felsic = increasing Si (silicon)
Mafic = increasing Fe, Mg, and Ca (iron, magnesium, and calcium)
intrusive vs. extrusive minerals in Igneous rocks
intrusive = slower cooling, coarse grained, and tends to have a more spotted look.
extrusive = faster cooling, fine grained, and tends to have a homogenous look.
primary minerals form…
during cooling of magma
secondary minerals form…
from chemical breakdown or alteration of primary minerals
what are examples of primary and secondary minerals?
primary minerals: quartz, feldspar
secondary minerals: calcite, clay minerals, Gibbsite
what mineral type forms during weathering?
secondary minerals
what is weathering?
all physical and chemical changes produced in rocks or minerals. occurs at or near the earth’s surface. facilitated by air, water, and organisms.
what is physical weathering?
breakdown or disintegration of larger rocks or rock fragments into smaller particles by physical force.
what is chemical (biogeo) weathering?
alteration and/or breakdown of initial mineral compounds through chemical reactions.
what are the four main physical weathering agents?
1) temperature (expansion, contraction, and exfoliation)
2) wind (erosion)
3) water and ice (erosion, freeze-thaw, and shrink-swell)
4) biota (plant roots, animals digging or walking)
what is exfoliation?
“peeling of rock” (usually Igneous) from outside in, caused by temperature and pressure changes. temp + pressure: expansion + contraction –> exfoliation (ex: Half Dome, Yosemite National Park)
when is biogeochemical weathering faster and slower and why?
chemical weathering is faster in warm and wet climates and slower in cold and dry climates. this is because the rocks are undergoing a chemical reaction that utilizes water either as a reactant or to dissolve and diffuse reactants. additionally, in higher temperature conditions, more collisions occur on the molecular level so it will occur faster.
describe freeze-thaw in terms of physical weathering
when water freezes into ice it expands and this expansion of water breaks sedimentary rocks into even smaller particles.
describe ice lenses in terms of physical weathering
nearby liquid water flows from wet to dry (icy) areas of soil. once the liquid touches the cold ice, its temp decreases causing some liquid water to freeze. as it freezes, the ice expands, pushing against nearby rocks and soil. this can crack open rocks, break up clumps of soil or push clumps of soil together.
do ice lenses or freeze-thaw result in more weathering?
ice lenses
how might streams or flowing water cause physical weathering?
smaller rocks in streams may tumble, roll, skip and bounce, scrape against each other, and hit larger rocks in the streambed.
how does wind cause physical weathering?
sand and other small particles get carried in the wind and over time those particles scrape and score against the outside of rocks and abrade them into smaller particles
how do plant roots cause physical weathering?
when plant roots grow and expand into the ground, they help crack open rocks and compress surrounding sediments and soils. they also make rocks push against other rocks which causes weathering
how do animals cause physical weathering?
animals cause physical weathering by burrowing, crawling/walking, and digging.
what are the 3 soil particle sizes?
(largest) sand –> silt –> clay (smallest). sand can weather into silt which can weather into clay. more physical weathering = more silt and clay particles.
what are the 6 types of chemical weathering reactions?
1) Hydration (w/ water)
2) Hydrolysis (w/ water)
3) Dissolution (w/ water)
4) Acid-base
5) Complexation
6) Redox
what is hydration?
process of adding water to chemical structure without forming covalent or ionic bonds with the rest of the structure
what is hydrolysis?
splitting water, the add H+ or OH- to mineral.
what is dissolution?
solubilize in water (surrounded by water molecules)
what are acid-base reactions?
acid donates H+ to base
what is carbonation?
an example of an acid-base reaction. dissolution of CO2; produces carbonic acid
what is complexation?
electronegative nonmental compounds (ligands) surrounding and bonding to a metal.
what are redox reactions?
electrons get donated from one molecule to another.
what types of rocks weather faster vs. slower?
sedimentary rocks weather faster than igneous rocks and metamorphic rocks
what types of minerals weather faster vs. slower?
felsic (Si) minerals weather slower than mafic (Fe) minerals. Mafic has more Fe (iron) = faster redox reactions = faster weathering
how might chemical and physical weathering affect one another?
the physical weathering increases surface area which allows more contact with water molecules. chemical weathering destructs and creates a weak spot which allows physical weathering to occur easier.
what happens to minerals dissolved in chemical weathering?
they form weathered minerals and ions which then either leach to groundwater, transport to streams and oceans, or precipitate to form secondary minerals
the Jenny equation describes what
the 5 factors of soil formation
what is the Jenny equation?
Si = f (cl, o, r, p, t)
Si = individual soil property
cl = climate (temp + precipitation)
o = organism (biota: microbes, vegetation, animals)
r = relief or topography (slope, aspect, landscape position)
p = parent materials (geological or organic precursors to soil)
t = time (how much time elapsed since parent materials began weathering)
which soil formation factor is a multiplier of 3 of the other factors?
time; the longer a soil has to form, the longer climate and organisms act upon each other and change the parent materials
what are the three general categories of parent materials?
1) organic
2) residual
3) transported
what are organic parent materials?
Organic Parent material = mostly dead and slowly decomposing plants (ex: peat + muck)
organic = of biological origin; contains carbon (C-C & C-H bonds)
what climate are organic plant materials typically found in?
cool, wet climates (wetlands). decomposition is much slower with a lack of oxygen and warmth. (common in Arctic and sub-Arctic regions)
what is the compositional difference between mineral soil and organic soil?
mineral soil = less than 20% organic matter (~99% of world’s soils)
organic soil = more than 20% organic matter (~1% of world’s soils)
how does mineral soil vs organic soil differ visually?
Mineral soils are typically much lighter in color than organic soils. Organic matter is very dark brown, almost black. Dark colored soils usually contain large amounts of organic matter, lighter soils less
organic matter
what are residual parent materials (Residium)?
parent material directly from solid bedrock (residual = left behind)
what are the four vectors for transported parent materials?
1) water
2) ice
3) gravity
4) wind
what is the term for stream-deposited parent materials?
Alluvium // alluvial parent material
(well sorted, rounded fragments because they’re being tumbled for long periods)
what is the term for lake-depositied parent materials?
Lacustrine
what is the term for gravity deposited parent materials?
Colluvium = colluvial parent materials. usually found at the bottom of mountains and hills. (poorly sorted because gravity acts the same on all rocks) (angular fragments because they usually break apart abruptly and they don’t “tumble” downwards for very long)
what is the term for ocean deposited parent materials?
marine parent materials. found in coastal areas and is mostly sandy; some silt and clay.
what is the term for ice deposited parent materials?
glacial till (poorly sorted materials because ice will plow and pick up everything without any order or reason, ice also grinds up rocks at the bottom)
glacial outwash parent materials occur when glaciers melt. is this considered glacial till or alluvium at that point?
alluvium parent materials because it’s deposited by water (glacial stream)
what is the term for wind deposited parent materials?
Eolian/Aeolian (think Sand Dunes, usually occurs in dry places). windblown silt sized particles are called Loess, and they are small enough to be moved considerable distances before being deposited)
what is the difference between sand and Loess?
sand = .5-2mm (water flows too fast between the sand particles so water doesn’t stay, and plants are scarce)
Loess = silt sediments = .02-.5mm (water flows much slower so silt sediments hold onto water better, hence allowing for more plants to survive)
how does the parent materials affect soil properties?
1) the younger the soil, the more soil properties will resemble the parent material (time)
2) as the weathering rate increases, soil thickness increases along with percent secondary minerals
3) initially soil particles resemble parent material in both mineral and particle size
how are temperature and reaction rates related to one another?
for every 10 degrees C increase in temperature, the reaction rate doubles (2x faster)
what is effective precipitation?
amount of rain/snow/hail reaching the parent material
more intense rainfall means a ______ rate of weathering
higher. more water is reaching the parent material
more transpiration and evaporation relative to precipitation means a _______ rate of weathering
slower. less water is reaching that parent material underground
if there is a slope, where does the most effective precipitation occur?
lower on the slope of the landscape. higher weathering rate occurs at lower slopes because water is moving from higher slopes and shedding into lower sloped areas
how does particle size affect the rate of weathering and effective precipitation?
the larger the particle size, the more water that is sinking deeper into the soil which results in a higher amount of weathering deep in the soil
what is the global aridity index?
the ratio of precipitation to potential evapotranspiration
soil depth increases with increasing …
temperature and precipitation. therefore, in arid climates the range of depth for the lower boundary of rock weathering is very shallow (<10m) and in humid climates the, the range of depth for rock weathering is much deeper (25-60m)
soil depth increases with ….
increasing weathering
what types of organisms (biota) affect soil?
1) plants
2) microbes and soil animals
3) humans
what is bioturbation?
the mixing of soil by organisms
generally, explain the affect plants generally have on soil
-plants influence organic matter accumulation, erosion rates, and physical and chemical weathering. plant roots absorb moisture from the soil which decreases the rate of chemical weathering. plants are also the primary source of organic matter in soils.
explain the affect microbes and soil animals have on soils
burrowing organisms mix the soil horizons (layers) together and aid in nutrient recycling which is called bioturbation. they also aid in organic matter breakdown and accumulation. they also provide soil stability and structure.
explain the affect humans have on soil weathering
-humans create mixing (tillage) in the soil.
-humans put pavement over the soil which is called soil sealing
-turning soils into landfills
tends to be destructive, not usually great but does depend on management practices
when thinking about plants altering soils, what two factors should you consider
type of vegetation (trees vs. grasses) and climate (wet vs. dry, cold vs. warm)
in grassland communities, plants produce _____ acid, resulting in a _____ pH and ____ earthworms which _____ the mixing of organic matter into topsoil which results in a _____ topsoil
less, higher, more, increases, thicker
in grassland communities, less acid means ____ leaching and ____ Ca. a _____ root turnover = _____ organic matter added to the soil.
less, more.
faster, more
tree roots produce more _____ than grassland roots do and they live _____
acid, longer
in tree dominant communities, plants produce _____ acid, resulting in a _____ pH and ____ earthworms which _____ the mixing of organic matter into topsoil which results in a _____ topsoil and _____ leaf litter
more, lower, less, decreases, thinner, thicker
in tree communities, more acid means ____ leaching and ____ Ca. a _____ root turnover = _____ organic matter added to the soil.
more, less.
slower, less
Conifers (evergreens) are ____ acidic and have _____ Ca vs. deciduous trees (broadleaves) are _____ acidic and have ____ Ca.
more, less
mildly, more
soil developing under what type of vegetation should chemically weather fastest?
Coniferous forests because they have more acid, which causes a promotion of the rate of chemical reactions in the soil
what is meso-scale heterogeneity?
in arid and semi-arid climates, there’s not enough water to support continuous vegetation coverage so plants grow in localized patches. in the soil under these plant patches there will be more organic matter and soil organisms.
what is relief/topography?
slope, aspect and position in the landscape
steeper slope = _____ soil depth with ______ layers
lower soil depth with less layers (underdeveloped)
lower elevation/less steep slope = _____ soil depth with ______ layers
greater soil depth with more layers (more developed)
at the bottom of a slope, moisture levels are _____ and _______ weathering occurs _______
higher, chemical faster
more sun = _______ weathering, _______ soil development and ______ soil
faster, faster, thicker
the sun comes from the _____, so south facing mountain slopes are ______ and will weather __________ than north facing slopes
South, warmer, faster
when the sun comes from the north, the _____ facing side is warmer and has _____ weathering
north, faster
what it aspect?
aspect is the cardinal direction that a slope is facing (N, S, E, + W)
soil higher up on the slope = ______ soil and more ________ reactions
drier, oxidation
soil lower on the slope = ______ soil and more _________ reactions
wetter, reduction
what is time a measure of in soil formation?
for how long climate, organisms, and relief/topography acted upon the parent materials
time is a _______ of ____ for climate, organisms, and relief.
multiplier of 3
more time = ______ effect of climate, organisms and relief, and _____ resemblance of the original parent material
greater and less
generally, older soils have ______ nutrient content, _____ particles and ______ secondary minerals
lower, smaller, more
generally, newer soils have ______ yet varying particle sizes and ____ secondary minerals
larger, less
what type of parent materials might you typically find at the top of a slope? middle of the slope? bottom of the slope?
top: residual parent materials (left behind bedrock)
middle: colluvial parent materials (gravity)
bottom: colluvial parent materials (gravity) or alluvial parent materials (stream)
is it hard to separate out the effects of vegetation and climate on soil formation?
yes, they’re very interrelated and challenging to separate based on their affects on soil formations
what are the 4 processes of soil formation and what do they entail?
1) additions- material entering the soil from above, below or horizontally (organic matter, organisms, groundwater, leaves, minerals)
2) transformations- one material/chemical becomes another (weathering)
3) translocations- lateral or vertical movement inside of the soil (nothing entering or exiting) (dissolved solutes moving)
4) losses- material exiting the soil from above, below, or horizontally (erosion, gases (CO2) evaporating and leaching)
what are the two steps in translocations?
1) Elluviation - the removal of soil material in suspension or solution from a layer of soil (“E” for exit)
2) Illuviation - the accumulation of material in a lower horizon, translocated from an upper horizon (“I” for incoming)
what is the difference between the four terms: alluviation, illuviation, eluviation, and colluviation
alluviation = the process of stream depositing parent materials
illuviation = the accumulation of materials in a lower horizon
eluviation = the removal of soil materials in suspension or solution
colluviation = the process of gravity depositing parent materials
homogenous materials become differentiated soil layers through …
soil formation processes
what is a soil horizon?
distinct layer of soil with unique properties. soil horizons differ in chemical composition, texture and/or color.
what is horizonation?
the separation of soils into distinct layers
what is soil texture?
the relative properties of sand, silt, and clay particles in a soil. clays are often translocated downwards.
together, the soil layers are called the _____ ________
soil profile
what are master horizons?
the broadest, most general horizon category.
what are the different soil horizons of a soil (top to bottom)?
top 2 bottom: O, A, E, B, C, R
O horizon: (organic litter)
A horizon: (topsoil, organic matter mixed with minerals (zone of addition))
E horizon: (zone of eluviation (loss))
B horizon: (zone of illuviation (accumulation))
C horizon: (unconsolidated parent material)
R horizon: (consolidated rock (bedrock))
what is my pneumonic for remembering the different soil horizons?
O, A, E, B, C, R
ostriches are enormous birds containing rizz
-the O horizon tends to have a _____ color.
-the E horizon tends to have a _____ color and is often _____ in texture.
-the B horizon tends to be more ______ than the horizons above it
-the C horizon if often the ______ ________ of the upper horizons
dark
lighter, sandier
clayey
parent materials
when describing subdivisions within master horizons, the 1st letter = ______ _______ and the 2nd letter/number = __________ or _______
master horizon
subhorizon or transitional horizon
transition horizons are transitional between …
two master horizons.
subdivisions/subordinate horizons provide __________ ___________ of master horizons
further characterizations
if the 2nd letter is lower case = ________
if the 2nd letter is upper case = __________
subdivision
transition between two horizons (first letter represents dominant horizon properties)
where do additions occur?
horizon A
where do transformations occur?
all horizons
where do translocations occur?
horizon E + B (zones of eluviation (exiting) and illuviation (incoming)
where do losses occur?
all horizons
are all horizons always present in soils?
nope, not all horizons are always going to be present
what is tillage?
the process of humans intentionally stirring up soils. tillage influences the productivity of soils and is designated by a small ‘p’ letter.
what is soil taxonomy (definition wise)?
a hierarchal grouping of soil bodies based on observable and measurable soil properties. we will use the UDSA classification system in this class
what the order of soil taxonomy from least specific to more specific?
(least specific) order, suborder, great group, subgroup, family, and series (most specific)
O, S, GG, S, F, S
what do we classify soils based on?
-diagnostic horizons
-their ind. properties: color, particle sizes, other moisture and temperature indicators
what does heterogeneous mean?
diverse in character or content (not uniform/homogenous throughout).
soils are ______ __________ because their properties vary vertically (horizons) and horizontally (landscape, vegetation, or human effects)
highly heterogenous
what is the term used to describe the smallest imaginary 3D unit displaying identifiable, unique soil properties?
a Pedon
a polypedon is comprised of what?
comprised of multiple pedons, together these are “a soil” or a soil individual
what is a diagnostic horizon?
layer or soil horizon whose properties meet certain criteria specified for the purpose of classification
what are the two types of diagnostic horizons?
1) Epipedon- diagnostic surface horizon (O, A)
2) Endopedon- diagnostic subsurface horizon (B, C, E)
what are the two major diagnostic Epipedons?
1) Mollic
2) Ochric
______ is dark colored, thick, has a pH between 6-8, and more than 0.6% organic carbon. ______ is light colored, thin and has low soil organic matter. both occur in the A horizon.
Mollic
Ochric
what are the 6 major diagnostic Endopedons?
1) Albic (E horizon)
2) Cambic
3) Duripan
4) Argillic
5) Natric
6) Calcic
________ is dense, cemented, and impermeable. _______ is light colored and has lots of elluviation. _______ is weakly developed B horizon with little to no illuviation.
Duripan
Albic
Cambic
______ is the accumulation of sodium (Na) and clay. _______ is the accumulation of clay. ________ is the accumulation of calcite carbonate (CaCO3) and/or dolomite (Ca, Mg) CO3.
Natric
Argillic
Calcic
how many soil orders are there? what are they organized based on?
- organized into groups based on soil properties such as diagnostic horizons, time, parent materials, and climate/biota.
______ are the youngest or most recently developed soils. they have no B horizon due to high erosion rates. they are typically located in desert regions (cold, dry) and have a slow weathering rate.
Entisols
_______ are the second youngest soils. they have a weakly developed B horizon (cambic), and are found in areas with moderate erosion rates (common on moderately steep slopes) and somewhat slow weathering (a little dry/cold, northeastern U.S.
Inceptisols
______ are weakly to moderately developed soils. they are formed from volcanic ash parent materials and contains poorly crystalline clay minerals (sphere/tube shape allows for a large water-holding capacity). the ash forms layers. they’re found near volcanoes (andes mountains) and have high organic matter and are very fertile. contain a melanic epipedon
Andisols
_____ are swelling clay soils that are found in arid and semi-arid regions (mostly dry grasslands). Shrink-swell causes mixing or inversion of the soil: during dry conditions, the soil is pulled apart and creates cracks/gaps in the surface that the topsoil then falls into. then during the wet season, the soil expands again and fills the cracks. slick-n-slides occur in this soil type.
Vertisols
_______ are organic, wetland soils (parent material = peat moss). 24-30% organic matter and 12-20% organic carbon. very wet flooded conditions cause OM decomposition to be very slow which causes the OM to accumulate. they have very large (>50% of soil profile) O horizons and have histic epipedons.
Histosols
_______ are permafrost soils found in very cold tundra biomes. permafrost = permanently frozen layers in upper 1m. experience mixing due to freezing + thawing = cryoturbation. contain pingos (ice mounds)
Gelisols
_______ are desert, arid soils that have a pale, Ochric epipedon. has endopedon with weak development (cambic) or carbonate, salt or clay accumulations. they experience slow chemical weathering due to dry conditions and physical weathering dominates. low in OM due to low plant growth. may form petrocalcic horizons if enough salt has accumulated.
Aridisols
petrocalcic horizons are very ___ and are used for storing …
solid/hard
airplanes/heavy things on top of (example from class)
_________ are dark, organic matter-rich, grassland topsoil. grasses increase pH which increases organic matter and _______
Mollisols
mixing
what type of soils are the most fertile (on average)?
Mollisols (soft, dark)
_______ are found in broadleaf (temperate) forests, usually deciduous and has mild acid weathering. there is a clay accumulation in the B horizon (called argillic endopedon). this soil is often quite fertile.
Alfisols
__________ are found in coniferous forests and coastal areas with a lot of sand (sandy parent material common). acidic needles and root exudates, causing a low pH which produces a lot of acid weathering. these soils have dramatic E and B horizons due to rapid elluviation and illuviation (from high acidity). this soil type tends to be not very fertile.
Spodosols
_________ are highly weathered tropical and subtropical soils. they’re acidic on average and low in Ca + Mg. compared to others, tends to be less productive.
Ultisols
__________ are extremely weathered, old tropical and subtropical soils. most common soil type in tropical rainforests, acidic and low in organic matter. they have 100% secondary minerals (not sticky, non-swelling) and poor fertility.
Oxisols
describe how soil nomenclature looks
5 parts: order to family (R 2 L)
series name: 1-2 simple words
what are the 12 soil order roots?
1) Ent - Entisols
2) Ept - Inceptisols
3) Ist - Histosols
4) Gel - Gelisols
5) Id- Aridisols
6) And - Andisols
7) Alf - Alfisols
8) Oll - Mollisols
9) Ert - Vertisols
10) Od - Spodosols
11) Ult - Ultisols
12) Ox- Oxisols
how is soil color classified (3) parts?
hue: red, green, yellow, etc. (number, letter)
value: lightness (number)
chroma: intensity or brightness (number)
how is soil color written out?
hue value/chroma
wet soil has a ______ value than dry soil does
lower
what does soil color tell us about soils?
-amount of OM (black/brown)
-mineral composition (Iron = red/oranges/colorful, Aluminum = gray, Manganese = black)
-precipitation of soluble salts and minerals
only _____ minerals produce red + orange colors
Iron (Fe)
what is Gleying?
greying of soil due to reducing conditions. gleyed soil indicates prolonged anaerobic (lack of O2) conditions and are common in very wet or flooded soils.
what causes gleying?
saturated (waterlogged) conditions, which accelerate iron leaching and leave behind mostly Aluminum minerals
Bg = _____ cambic horizon
gleyed
_______ is the adjacent bright and dark colors caused by alternating wet and dry conditions
mottling
what does white coloration indicate?
salts are present (salt = ionic compound).
what are evaporate minerals?
inorganic salts left behind when salty water evaporates
what is soil texture?
relative proportions of sand, silt and clay particles in a soil. this does not include organic matter –> mineral particles only
sand + silt + clay = ______ ________
soil separates
what are soil textural classes?
qualitative categories used to describe soil particle distributions.
in order to identify a soils’ textural class, you have to use a ________ __________
textural triangle (USDA)
what are the three different types of soil separates?
-sand: largest (.05-2mm)
-silt: middle (.002-.05mm)
-clay: smallest (
what are the properties of sand?
-shape: round or irregular (.05-2mm)
-feel: gritty, not sticky, not plastic
-surface area: low
-average pore size: large (low water and nutrient-holding capacity, rapid infiltration and drainage)
what are the properties of silt?
-shape: round or irregular (.002-.05mm)
-feel: smooth
-surface area: medium
-average pore size: medium (holds moderate amount of water; provides a large amount to plants)
what are the properties of clay?
-shape: plate-like to rounded shape; very thin layers
-feel (wet): sticky and plastic
-feel (dry): hard and cloddy
-surface area: very high
-average pore size: lowest average pore size, highest total pore space, + high water holding capacity
if a large particle is broken down into smaller particles, the total surface area ________
increases exponentially
what are the three types of rock fragments (large particles)?
-gravel or pebbles: 2-75mm
-cobbles or channers (angular): 75-250mm
-stones or boulders: >250mm
if the soil composes of more than 15% rock fragments, you add a _________ _______ modifier to the soil textural class.
coarse fragment modifier (ex: gravelly sandy loam)
describe Stokes law
Stokes law describes settling velocity (V) of soil particles as a function of particle diameter (d). when particle diameter increases, the settling velocity of a particle increases (settling time decreases).
what are the 4 different methods to determine soil texture?
-feel method
-hydrometer sedimentation method
-sieving method (good for sandy soils)
-laser diffraction method
what is soil structure?
spatial arrangement of particles into complex aggregations, pores, and channels
_______ is many soil particles held in a single mass or cluster
an aggregate
_____ is the natural unit of soil structure such as an aggregate, crumb, prism, block, or granule (large aggregate)
Ped
what are pores?
spaces between soil particles (containing air or water)
______ form from plowing or excavation (man-made, not natural)
clods
can aggregates be found within one another?
yes, macro-aggregates have micro-aggregates within them
what affects do soil structure have on soil properties?
-porosity
-heat transfer
-aeration
-movement of water + nutrients
all of these affect’s result in different ecosystem services
how can soils be physically pushed together?
-wet-dry, shrink-swell
-freeze-thaw
-organisms: burrowing animals and roots
what can soils be chemically bound together by?
-clays
-ions, salts, oxides
-organic matter
fungal hyphae (root-like structures) ______ aggregates and _____ soil particles together. plant roots also help hold larger aggregates and peds together.
enmesh
bind
what is flocculation?
the attraction and binding of clay-sized particles to each other (due to opposite charges attracting to one another)
more positive cation charge = ______ flocculation = _______ aggregation
more
better
true/false: sodium (Na+) causes more dispersion. calcium (Ca2+) and aluminum (Al 3+) causes more flocculation.
true
soil organic matter helps _____ aggregates from slaking, or falling apart when ______
prevent
wetted
a fungus growing on a corn plant produces _______
glomalin (green color) … which improves aggregate protection, keeping carbon locked away for up to 100 years.
draw and/or explain what a good soil structure looks like compared to a poor soil structure
poor structure: very small pores, low porosity, dense –> poor aeration, slow water infiltration, and high root penetration resistance.
good structure: mix of small and large pores, higher porosity, less dense –> good aeration, rapid water infiltration, and low root penetration resistance.
what is the formula for the density of a soil?
mass of soil / volume of soil
what is formula for soil particle density (Dp)?
Dp = mass of particles / volume of particles. (not influenced by particle size or soil structure)
what is soil bulk density (Db)?
Db = mass of dry soil / volume of dry soil (includes soil particles and air) (dry soil, not wet)
what is the formula for calculating the volume of something?
volume = π * radius^2 * height
what are the units of soil bulk density (Db)?
g/cm^3 or Mg/m^3
what is the typical soil bulk density for loamy soils?
1.1-1.4 g/cm^3
how can you measure bulk density in the field?
using the core method
what is porosity?
the percentage of pore space in a soil
what is the formula for porosity?
porosity = 100 x (1-Db/Dp)
(always assume Dp = 2.65g/cm^3)
as particle size decreases, soil bulk density ______ and total porosity _________
decreases
increases: larger particles have fewer micropores in between them, leading to a lower bulk density
as bulk density increases –> soil porosity ________
decreases
what are the processes involved in aggregate formation and stabilization?
physical: shrink-swell and freeze-thaw.
chemical: organic matter accumulation, flocculation of clays, and precipitation of salts and oxides.
biological: roots and animals pushing soil particles, production of cementing agents (glomalin), and enmeshment by fungal hyphae.
what are the factors affecting soil bulk density and porosity?
-soil texture and structure
-soil organic matter
-depth in soil
-management practices (tillage, soil amendments, crop residues, cover crops, and compaction)
as soil organic matter increases, soil bulk density ______ and porosity ________
decreases
increases
with an increase in depth, soil bulk density _________
decreases
what are the associated problems with having a high soil bulk density?
-decreased aeration
-decreased water infiltration
-decreased water drainage
-increased root penetration resistance
what is the size of macropores?
> 80 micrometers
what is the size of mesopores?
30-80 micrometers
what is the size of micropores?
5-30 micrometers
explain how soil texture affect soil porosity
as particle size decreases ….
-the number of pores increases
-the average size of pores decreases
-total porosity increases
-bulk density decreases
what has a higher total volume: 42g of sand or 42g of clay?
42g of clay because the total porosity increases and the bulk density decreases
a higher soil organic matter = _______ soil bulk density and _______ porosity
lower
higher
what is soil tilth?
the physical condition or quality of the soil related to plant growth
what factors does soil tilth depend on?
-soil structure
-aggregate stability
-bulk density
-aeration
-water (infiltration rate, drainage rate, and water-holding capacity)
what is tillage and what impact does it have on soils?
tillage is the practice of mixing up soils using different machinery (plows, discs, and cultivators). tilling makes it easier for plants to break through the soil and tends to break up native weeds and grasses already present in that soil. however, tillage usually destroys soil structure and their aggregates.
what is conservation tillage?
tillage leaving at least 30% of plant residues on soil surface.
less tillage = _____ plant residue left on soil surface = _____ organic matter and _____ erosion/crusting = _____ soil structure/tilth
more
more
less
better
soil aggregates can also remain intact which also helps improve tilth
what is compaction?
occurs when soil particles are pressed together from the downwards force of foot or vehicular traffic on the soil.
compaction ________ bulk density, ________ porosity and ______ aeration
increases
decreases
decreases
what is soil crusting? (another effect of tillage)
occurs when there are no plant residues leaving the soil exposed. rain disperses the aggregates –> clays form a surface seal, and that surface seal hardens into a crust. this makes it nearly impossible for plants to grow
more vehicle traffic = _____ compaction = ______ bulk density = ______ plant productivity
more
greater
lower
describe how tillage impacts vary based on short term vs long term
short term: decreases bulk density and increases porosity
long term: increases bulk density and decreases porosity and soil organic matter
