week 1 Flashcards
1
Q
5 basic materials of soils
A
- mineral solids (45-49%)
- organic solids (1-10%)
- Air (20-30%)
- Water (20-30%)
- Organisms (<1%)
2
Q
porosity
A
total void volume of a soil; remains the same regardless of wetting or drying, or water:air ratio.
3
Q
mineral solids
A
- clay: <.002mm
- silt: .002 - .05mm
- sand: .05 - 2mm
- gravel, cobbles, stones: > 2mm
- Primary minerals: formed by geologic processes, detrital, inherited by the soil
- Secondary minerals: formed by pedogenic processes, usually clay-sized
4
Q
organic solids (SOM / OM)
A
Important because:
- holds water in soil (micropores)
- binds soil particels together; aggregates into clumps
- nutrient source
- energy source for organisms
3 forms:
- recognizable detritus from plants/animals on surface or just below
- Humus: unrecog. OM; decomp’d and synth’d into brown/black OM
- Colloidal OM: small enough to stay suspended in liquid; incl. soluble organics and organic acids
5
Q
soil water
A
important aspects:
- water held by soil is available for uptake by plants/animals
- with dissolved elements/compounds make up the
* *soil solution:** surround roots, interface b/t inorg. particles, OM, and organisms; part of transfer system for nutrients, etc - moves materials through and w/in soil horizons
- removes material by leaching
6
Q
soil air
A
- higher CO2 than atmos. due to resp of roots/orgs
- lower O2 than atmos. due to root uptake
- rel. humidity usally 100% except in very dry desert soils
- effected by porosity & aeration
- soil air can be trapped below soil water
7
Q
soil organisms
A
- physical breakdown of biotic residues
- decomp. or org. matter
- release of
- exudates to aggregate soil particles
- acids that weather rock
- form humus & colloidal org. matter
- mix soil
8
Q
4 keys to productivity
A
- nutrients
- water
- oxygen / air
- anchorage
9
Q
civilizations dev’d in areas w/ ____ ____, & where they’d be ______, like _____
A
- rich soils; replenished; deltas
- Egypt: Nile
- China: Yellow River
- Tigris / Euphrates
10
Q
soils usually rated in terms of ___ ___
A
plant growth
11
Q
pedological definition of soil
A
soil is a natural body of mineral & organic matter that changes over time in response to environmental factors & biota
12
Q
soil morphology is…
A
the physical struture of the soil; examined w/ the soil profile
13
Q
soil horizons are…
A
- distinct layers formed by pedogenic processes
- distinct differences in:
- OM
- color
- sand/clay %
- chemical composition
14
Q
O horizon
A
- OM: but can be different types
- fresh litter & well-decomp’d humus
- usually above mineral soil (forest)
- common and very deep in wetlands
- seldom found in grasslands
15
Q
A horizon
A
- surface mineral horizon, darkened by OM
- may have properties from cultivation
- usually more fertile
16
Q
E horizon
A
- Eluviated mineral hzn where dominant feature is a LOSS of clay, iron, aluminium, OM, etc
- loss is due to leaching (causing a gray/white color)
17
Q
B horizon
A
- mineral hzn w/ either or both:
- illuvial increase in clay, Fe, Al, OM… from above (E)
- substantial alteration of original parent material that eliminated rock structure, forms clay or oxides (giving color)
- orangish, yellowish, greyish
18
Q
C horizon
A
- mineral hzn that has little alteration of original PM
- lacks properties of AEB hzns
- lies outside of most biological activity
19
Q
R
A
- rock material
- _not_ a horizon
20
Q
L horizon
A
- limnic material, uncommon (but occ. in PacNW)
- lake deposits
- full of diatoms, clay, OM
- @ bottom of wetlands
21
Q
transition hzns
A
- transition btwn 2 masters
- dominant hzn listed first:
- BC: smooth transition w/ B dominant
- A/B: interfingered w/ A dominant
22
Q
subordinate O hzn designations
A
- Oi: little decomp, OM still recognizable
- i = fibric
- Oe: intermediate
- e = hemic
- Oa: highly decomp’d, OM not recognizable
- a = sapric = saprophyte
23
Q
Ap
A
plowed; structural change
24
Q
subord: t
A
accumulation of silicate clays (Bt)
25
Q
subord: k
A
accum. of carbonate (Bk, Ck)
26
Q
subord: s
A
- accum. of sesquioxides (Fe/Al)
- orange-reddish color
- (Bs), illuvial
27
Q
subord: h
A
- accum. of humified OM (well decomp’d)
- Bh, Bhs, illuvial
28
Q
subord: g
A
- gleying, waterlogging, anaerobic, wet soil
- loss of O2 makes Fe grey/mottled
- Bg, Cg
29
Q
subord: w
A
- some development of color/clumps, but not well developed
- Bw
- *** B always gets a subord, so Bw if nothing else is special about it
30
Q
subord: b
A
- buried
- Ab (an A under other O, A, & B)
31
Q
sources of color
A
- OM: humus… black/brown
- Fe oxides: orange/red/yellow
- carbonates: white
- bare mixed mineral grains
- b/w, which eyes avg to grey
- fresh rocks/minerals
- waterlogged
- leached
32
Q
describing color
A
- hue: basic/primary color
- value: light/dark
- chrome: intensity/brightness
- ex: 10YR 4/4
- shade 10 of yellow-red
- value: 4
- chroma: 4
33
Q
soil texture
A
- proportion of various size particles < 2mm
- clay: < .002mm (aka 2 microns)
- silt: .002 - .05mm
- sand: .05 - 2mm
[gravel < cobble < stone]
note: texture doesn’t change w/ human impact unless we add or remove soil
34
Q
texture: sand
A
- rounded, irregular, blocky
- not plastic or sticky; not moldable
- larger pores -> water/air can move quickly/easily
- good aeration
- usually quartz & other primary minerals
- can get coated w/ clay, OM, oxides
- low low nutrition
35
Q
texture: silt
A
- similar to sand, but smaller, so smaller pores
- still not very plastic, but OK aeration
- still low nutrition
36
Q
texture: clay
A
- usually platey, sometimes rounded
- plastic, sticky, moldable
- hold water tightly (b/t plates of clay)
- made of secondary minerals
- chemical composition is variable, can be a nutrient src
37
Q
plastic limit
A
% of moisture at which it starts deforming/damaging the soil
38
Q
liquid limit
A
% of moisture at which the truck gets stuck
39
Q
physical props of clay
A
- shrink/swell
- cohesion: binds particles -> sharp edges in soil profile
- soil strength: capacity of a soil to resist stress; influenced by moisture, clay content, OM…
40
Q
soil classes
A
- sandy > loamy > clayey
- in the lab: sedimentation, V = kd2
- larger particles fall faster
41
Q
soil structure
A
- arrangement of soil particles into
- naturally form in soil
- can vary by horizon
42
Q
soil structure types
A
- plate-like: B or C, rocks, sediments
- prism-like: B, semi-arid -> arid;
- commonly grasslands; rarely forests
- block-like: B, forests
- spheroidal: A, grasslands, fine roots
- massive: all particles stuck together (w/ binding agent)
- single-grained: no aggregation, usually sandy soils
*** aggregation is usually a good thing, as it resists erosion
43
Q
promoters of soil structure development (7)
A
- climate: wet/dry, freezing/thawing
- clays
- OM
- oxides
- plant roots -> exudates -> adhesives
- soil organisms (ex: slugs)
- salts, carbonates
44
Q
soil depth
A
- volume of soil available to roots
- influences growth by affecting nutrition & moisture avalability
- anchorage / support
-
Effective Rooting Depth
- depth at which the roots can continue to be active during the entire growing season
- deeper soils are usually better (> 90% of the time)
- … but super deep tends to be super old, so likely running out of nutrients
45
Q
soil forming factor fathers
A
- Dochuchaev: father of pedology -> cropt
- -> Hans Jenny (sp?): 1st to try to quantify
46
Q
sequences
A
soil formation due to ___ when all other SFFs are held constant
- climosequence
- toposequence
- biosequence
- (PM-sequence?)
- chronosequence
47
Q
curve of clay formation rate looks similar to…
A
a weathering curve; that is…
more precipitation = faster clay formation & faster weathering
48
Q
qty of soil OM is highest in…
A
- temperate regions (& lowest in arctic and tropics)
- exception: wetlands have high SOM even in Arctic, due to low decomp rates
49
Q
loess
A
a loosely compacted yellowish-gray deposit of windblown sediment of which extensive deposits occur
50
Q
soil association
A
- group of soils that occur together in a characteristic pattern across a landscape
- based on parent material + topography
51
Q
SFF: relief/topography
A
- effects of aspect
- slope & elevation
- slope & slope position
- topo can effect microclimate
- alter Temp, moisture, rates of change
- depressions -> water pooling, frost pockets
- south slope: warmer, drier soil
- topo changes soil movement, patterns of
erosion / accumulation - topo effect vegetation
- vally bottom -> riparian: wetter, cooler, more hardwoods, fewer conifers
52
Q
SFF: time
A
- how long has parent mat. neem exposed to pegoenic processes
- absolute time vs. relative amount of development
- glacier bay: 250 years for well-dev’d soil is crazy fast, caused by high amounts of rainfall & salmon spawning
53
Q
SFF: parent material
A
- rock/mineral material in which soil forms
- can be OM too!
- Primary Minerals -> weathering ->
- altered solids -> more weathering ->
- ions, soil solution
- new minerals
- Secondary Minerals
- layer silicate clays
- oxides (esp. Fe & Al)
- amorphous clay-sized minerals
54
Q
Layer Silicate Clays (secondary minerals)
A
- tetrahedral sheet
- O-2, Si+4
- octahedral sheet
- O-2 or OH-
- Al+3, Mg+2, Fe+2, Fe+3
- expansion properties due primarily to whether or not the clay carries a charge, caused by
- *isomorphic substitution**
- tetra: Al+3 replaces Si+4
- octa: Al+3 replaces Mg+2 or Fe+2
- 1:1 (tetra:octa)
- Kaolinite: non-exp, 0 charge per unit cell
- coarse size, low plasticity, low shrink/swell
- Kaolinite: non-exp, 0 charge per unit cell
- 2:1 (tetra:octa)
- Vermiculite: exp, -.5 to -.9 charge
- medium size, medium plast, medium sh/sw
- Montmorillonite (smectite): very exp, -.4
- small size, high plast, high sh/sw
- Vermiculite: exp, -.5 to -.9 charge
- Muscovite
- primary mineral (above are all secondary)
- non-expanding
- -1 charge
55
Q
cation exchange capacity (CEC)
A
- clays have a net negative charge
- cations are used to balance that charge
- in secondary minerals, cations are not well bonded to the clay, so can exchange w/ each other
- exchange rxns are how soils store nutrients in a way that plants can access
- Factors:
- concentration of ions in solution
- relative strength of attration of cations
- Al3+ > (H+) > Ca2+ > Mg2+ > K+ > NH4+ > Na+
