week 1 Flashcards
(55 cards)
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
subord: k
accum. of carbonate (Bk, Ck)
26
subord: s
* accum. of **_s_**esquioxides (Fe/Al)
* orange-reddish color
* (Bs), illuvial
27
subord: h
* accum. of **_h_**umified OM (well decomp'd)
* Bh, Bhs, illuvial
28
subord: g
* **_g_**leying, waterlogging, anaerobic, **_wet_** soil
* loss of O2 makes Fe grey/mottled
* Bg, Cg
29
subord: w
* some development of color/clumps, but not **_w_**ell developed
* Bw
* \*\*\* B **_always_** gets a subord, so Bw if nothing else is special about it
30
subord: b
* **_b_**uried
* Ab (an A _under_ other O, A, & B)
31
sources of color
* 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
describing color
* hue: basic/primary color
* value: light/dark
* chrome: intensity/brightness
* ex: 10YR 4/4
* shade 10 of yellow-red
* value: 4
* chroma: 4
33
soil texture
* 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
texture: sand
* 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
texture: silt
* similar to sand, but smaller, so smaller pores
* still not very plastic, but OK aeration
* still low nutrition
36
texture: clay
* 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
plastic limit
% of moisture at which it starts deforming/damaging the soil
38
liquid limit
% of moisture at which the truck gets stuck
39
physical props of clay
* 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
soil classes
* sandy \> loamy \> clayey
* in the lab: sedimentation, V = kd2
* larger particles fall faster
41
soil structure
* arrangement of soil particles into
* naturally form in soil
* can vary by horizon
42
soil structure types
* 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
promoters of soil structure development (7)
1. climate: wet/dry, freezing/thawing
2. clays
3. OM
4. oxides
5. plant roots -\> exudates -\> adhesives
6. soil organisms (ex: slugs)
7. salts, carbonates
44
soil depth
* 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
soil forming factor fathers
* Dochuchaev: father of pedology -\> cropt
* -\> Hans Jenny (sp?): 1st to try to quantify
46
sequences
soil formation due to ___ when all other SFFs are held constant
* climosequence
* toposequence
* biosequence
* (PM-sequence?)
* chronosequence
47
curve of clay formation rate looks similar to...
a weathering curve; that is...
more precipitation = faster clay formation **_&_** faster weathering
48
qty of soil OM is highest in...
* temperate regions (& lowest in arctic and tropics)
* exception: wetlands have high SOM even in Arctic, due to low decomp rates
49
loess
a loosely compacted yellowish-gray deposit of windblown sediment of which extensive deposits occur
50
soil association
* group of soils that occur together in a characteristic pattern across a landscape
* based on parent material + topography
51
SFF: relief/topography
* 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
SFF: time
* 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
SFF: parent material
* 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
Layer Silicate Clays (secondary minerals)
* 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
* 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
* Muscovite
* _primary_ mineral (above are all secondary)
* non-expanding
* -1 charge
55
cation exchange capacity (CEC)
* 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+
