ENVS*2060 Midterm

Horizon characteristics

name, thickness & depth, colour, structure, texture, consistence, type of boundary, and pH

Thickness & depth

1st horizon = 0-30cm

2nd horizon = 30-65cm

3rd horizon = >65cm

Colour

helps us understand about organic matter content, gleying and eluvation (redox potential) occuring in soils; Munsell chart (hue, chroma, value)

Structure

arrangement of individual (primary) soil particles into recognizable secondary structures - think "building"

Structure types:

(1) single grain, (2) massive, (3) platy, (4) columnar, (5) blocky, (6) granular

(1) Single grain

no structure; sandy soils because sand does not have aggregate

(2) Massive

not much large pore space and does not conduct air well; has usually already been compacted and thus roots have trouble growing

(3) Platy

horizontal structure units with not many cracks for water, air, or roots to travel through; found in surface & subsurface horizons due to compaction (clay soils)

(4) Columnar

water & nutrients can go in and out as the soil dries out or shrinks (poorly drained soils); undesirable for growth - vertically oriented pillars

(5) Blocky

lots of large aggregates & common in B horizons, which promote drainage, aeration, and root penetration

(6) Granular

aggregates separated in loosely packed arrangements (typical of horizons with high organic matter & grass land soils)

Texture

relative proportion of mineral particles of different sizes:

sand = 2.0-0.05mm

silt = 0.05-0.002mm

clay =

Consistence

how sticky or plastic a wet soil is; vs. how friable or firm a dry soil is

a qualitative measure on dry & wet soils

Type of boundary

how distinct they are and consistent in the landscape; horizons can flow together or have very defined boundaries between them

pH

reflection of mineralogy of soil; could be high due to presence of carbonate; & management will have effect

A-horizon

near the surface; elevated accumulation of organic matter creating darkened minerals

B-horizon

subsurface horizon of accumulation (illuviated) - soluble salts, clays, iron & humus

C-horizon

least weathered & relatively unaffected by pedological processes; parent material

Eluviated

transportation of dissolved or suspended material within the soil by the movement of water when rainfall exceeds evaporation

Illuviated

introduction of salts or colloids into one soil horizon from another by percolating water

LFH

forest humus layer

Of

largely fibric material, early stages of decomposition

Om

largely mesic material, intermediate stage of decomposition (medium)

Oh

largely humic material, advanced stage of decomposition (well-decomposed)

Ah

dark coloured horizon enriched in organic matter

Ap

similar to Ah only subjected to cultivation

Ae

light coloured horizon eluviated in clay, Fe, Al, C

Bf

enriched in Fe & Al

Bt

enriched in clay (German "T" word)

Bn

enriched in sodium (Na) - Western Canada

Bm

horizon slightly altered by pedological processes

g

evidence of reduced conditions

k

containing calcium salts

s

containing soluble salts

ss

slicken slides - wedge shaped peds

v

vertical crack

y

effected by cryoturbation (frozen-stirred up)

z

layer of permafrost (frozen continuously)

Mineral soil formation:

forms top-down; weathering at surface; C-horizon is raked to surface by glaciers; OM accumulates on surface, begins to elevate down from B horizon

Organic soil formation:

forms bottom-top; forms in wet environments; decomposition is slow

Processes leading to horizon formation

additions, losses, transfers, transformations

Pedological processes:

(1) time, (2) organisms, (3) topography, (4) parent material

(1) Time

progressive weathering (transformation, losses, transfers, translocations)

(2) Organisms

source of photosynthetic carbon (contributes to weathering & development of soil structure)

(3) Topography

drainage, seasonal average soil water content; erosion; translocation

(4) Parent material

bedrock (going through weathering); glaciers & melt water (moving, sorting, re-depositing)

the bedrock determines chemical composition and glaciation determines texture

Igneous rock

formed from cooling molten rock at or below the surface

Sedimentary rock

formed when particles of sand, dust, soil, are deposited into horizontal layers

Metamorphic rock

forms from an existing rock that is changed by heat, pressure, or chemical reactions

Canadian system of soil classification

(1) order (10 different orders), (2) great groups, (3) subgroups; (4) families, (5) series (very specific)

Regosol

recognized for no B horizon; not enough time to develop (young soil), seen in recently disturbed areas; addition of organic matter creates A horizon

(Ah --> Ck)

DH= Ah

Brunisol

a forest soil with a mildly-developed Bm horizon (altered by pedological processes) - something accumulated, but not enough time to know; Ah organic material added - 9% CAN area cover

(Ah --> Bm --> Ck)

DH= Bm

Luvisol

forested soil with a Bt horizon (enriched in clay due to chemical weathering of limestone solubilizing, but very small amount; parent material from sedimentary rock); clay layers around soil pores due to water pressure moving down - dominant process is eluviation of clay from Ae horizon to the Bt horizon - 9% CAN area

(Ap --> Ae --> Bt --> Ck)

DH= Bt

Grey luvisol

a difference in the Bt and Ae horizon size; has leaf litter laying on surface instead of organic matter inside of Ah; not as ideal for growing

Podzol

forest soil associated with coniferous vegetation on igneous rock derived parent materials; high acidity in A-horizon results in bleached Ae horizon that deposits Fe and Al into the B-horizon to create ideal conditions for potato growth - 16% CAN area cover

no more Ck, just C, lowering carbonates and pH in soil to make it more basic (metals more mobile);

(LFH --> Ae --> Bf --> C)

DH= Bf

Gleysol

gleyed-horizon (low oxygen environment; oxidizes iron to give blue/grey colour-Bg); yellow pockets in soil are well oxygenated areas

(Ah --> Bg --> Ckg)

DH= Bg

Black Chernozem

grassland soil mostly on prairies with high levels of organic matter additions (deep organic horizon) from roots of grasses; Bm horizon moves up; not effected much by salt

(Ah --> Bm --> Ck)

DH= Ah

Light-brown Chernozem

less organic matter in soil, less precipitation, less overall water, more demand for water in evapotranspiration in soil

Solonetz

grassland soil with high sodium levels in B-horizon, and saline C horizon material; evaporation tends to bring salt water upwards, salt stays in water longer & does not let plants germinate; found in lower area terrain

(Ah --> Ahe --> Bnt1 --> Bnt2 --> Csk)

DH= Bnt

Vertisolic

associated with high clay glacio-lacustrine landscapes; characterized by shrinking & swelling clays; most water exists between layers where pores exist - vertic or slickenslide horizon within 1m of surface

DH= Bss or Css

Organic

accumulation of organic material (peat) in water saturated conditions; they are most commonly associated w/ boreal forest soils - BAD base for building - found in high amount in Canadian shield

(Of --> Om --> Oh)

DH= O-horizon

Cryosol

frozen soils that have permafrost; most common up North; turbic = something stirred up; has Z-horizon - 40%

(Ah --> Bmy --> C)

DH= Bmy

Soil assists plant growth by

(1) providing physical environment; (2) water from soil; (3) aeration to provide oxygen through roots; (4) source of nutrients

Soil as rooting medium

(1) root space; (2) amount of space - porosity; (3) continuity of pores; (4) strength of soil material (ease of deformation)

Significance of texture

total volume & size of pores (water movement, aeration); ease of root penetration; ease of fragmentation, cultivation; surface area

Stokes law

T = h / Kr^2

Drying & wetting

shrinking, formation of cracks & re-swelling; plains of weakness

Freezing & thawing

affects rooting systems, creates ice lens pushing roots out of ground and destroying sidewalks

Stabilizing structure

clay (cementing); organic matter; roots, fungal hyphae (enmeshment); and oxide coating (Fe) (cementing)

Particle density (PD)

Ms (mass of soil oven dry) / Vb (volume of bulk soil without pore space)

Bulk density (BD)

Ms (mass of oven dry soil) / Vs (volume of soil solids)

Pore space ratio (PSR)

1 - BD / PD

Higher BD =

lower PSR

Lower BD =

higher PSR