Lecture 2: Formation of soils from parent materials

Question 1

Climate (Cl-O-R-P-T)

Answer 1

-most influential factor on parent material because it determines what kind and how intense the weathering will occur in that area
-temperature: every 10 degree rise in temp double the rate of biochemical rxns
-effective precipitation: water must penetrate the regolith to be effective in soil formation

Question 2

Organisms (Cl-O-R-P-T)

Answer 2

the type of vegetation that is growing in that area, as well as the land use, affects the soil layers. (eg. a plowed field vs a forest)

Question 3

Relief (Cl-O-R-P-T)

Answer 3

Soils on a slope LOSE material due to gravity. Soils in flat areas GAIN materials especially from the fallen materials of the slope.

Question 4

Time (Cl-O-R-P-T)

Answer 4

Younger soils typically have less layers than older soils. Older soils also may not have as many nutrients.

Question 5

When does pedogenesis begin?

Answer 5

When horizons that are not present in the parent material begin to appear in the soil profile

Question 6

What is pedogenesis?

Answer 6

Soil formation

Question 7

The 4 basic processes of pedogenesis

Answer 7

-Additions
-Losses
-Translocations
-Transformations

Question 8

Topsoil Letters

Answer 8

A (or E)

Question 9

Subsoil

Answer 9

B

Question 10

Regolith

Answer 10

C (or R)

Question 11

Topsoil: A Horizon

Answer 11

-darker
-mineral soil + organic matter
-water flows through (loses minerals bc of this)

Question 12

Topsoil: E Horizon

Answer 12

-grey to white
-mostly sand
-zone of intense leaching
-Fe- and Al- oxides have been eluviated
-common under forest because of HUMIDITY and ACIDIC soil pH

Question 13

Subsoil: B Horizon

Answer 13

-accumulation of mineral particles leached from topsoil like clay and salts
-less organic matter
denser
-more difficult for plant roots and water to penetrate
-usually red, brown, or orange

Question 14

Regolith: C Horizon

Answer 14

-most like parent material
-very little biological activity and weathering
-can be dug with a shovel

Question 15

Regolith: R Horizon

Answer 15

-hardpan (compacted)
-composed of compacted and/or cemented clay with calcium carbonate, iron oxide, manganese or silica
-unaltered parent material, consolidated bedrock
-impermeable
-can’t be dug with a shovel

Question 16

Compared to the B horizon, the A horizon is likely to be higher in ___

Answer 16

Organic matter

Question 17

Master Horizons Order

Answer 17

O
A or E
B
C or R

Question 18

O Horizon

Answer 18

-organic layer
-not usually in grasslands
-most common in forests

Question 19

Oi

Answer 19

surface- undecomposed leaves and twigs

Question 20

Oe

Answer 20

middle-partially decomposed

Question 21

Oa

Answer 21

bottom- very dark, well decomposed (soapy)

Question 22

Minerals

Answer 22

naturally occurring inorganic element or compound with repeating structure.

Question 23

Rocks

Answer 23

made up of a bunch of different minerals

Question 24

Primary mineral

Answer 24

solidified from molten magma/lava

Question 25

Secondary mineral

Answer 25

recrystallized products of the breakdown/alteration of primary minerals

Question 26

Resistance of primary minerals

Answer 26

primary minerals containing Fe (iron) and Mg (magnesium) are less stable. the more stable ones have Al (aluminum) and K (potassium)

Question 27

Resistance of secondary minerals

Answer 27

Aluminum silicates and minerals containing iron are more resistant and those containing calcium are less resistant.

Question 28

Physical Disintegration and examples

Answer 28

physical breaking of rock into smaller and smaller pieces without changing the mineralogy. (eg. jointing, thermal expansion, frost wedging)

Question 29

Chemical decomposition and examples

Answer 29

breaks down rock components and internal structures of minerals. converts primary minerals to secondary and releases plant nutrients in soluble form (eg. hydrolysis, dissolution, oxidation) *needs water and acids

Question 30

Dissolution

Answer 30

minerals are soluble in water or weak acids. involves breaking relatively weak IONIC bonds

Question 31

Carbonate dissolution

Answer 31

acidic water dissolves calcite. this process dissolves limestone and carries the cations away. formation of caves and karst. dissolved products carried to ocean.

Question 32

Hydrolysis

Answer 32

H+ ion attacks minerals, replaces other cations in the crystal. Silicates react with acidic water to form: -secondary minerals -dissolved ions -dissolved silica

Question 33

Oxidation- Reduction

Answer 33

Formation of rust on metal

Question 34

Biogeochemical weathering

Answer 34

Chemical weathering enhanced by inorganic acids and organic acids.