Chapter 1 Topic 3

Question 1

What are soils?

Answer 1

mixtures of organic matter (OM), minerals (including fragments), gases, liquids that support life at the
surface of the Earth

Question 2

Where do the organic matter in soils come from?

Answer 2

The organic matter in soils mostly comes from dead plants

Question 3

Where do the minerals in soils come from?

Answer 3

Minerals are usually products of weathering

Question 4

What two type of soils are there?

Answer 4

Organic soils (when soil has high than 20% organic matter) and mineral soils (when soil has less than 20% organic matter)

Question 5

How do organic soils form?

Answer 5

Form in environments with a lot of plants ( a lot of leaf litter) and an environments that perserves these plants such as anoxic wetlands (bogs, swamps) as plant falls into water and stay perserved.

Question 6

What are mineral soils mainly made of?

Answer 6

Minerals and rock fragments formed by weathering of big rocks.

Question 7

What is regolith?

Answer 7

Is sediment

Question 8

Soils form from what two things?

Answer 8

Regolith and organic matter

Question 9

Is soil regolith?

Answer 9

Yes, but it’s regolith that supports plant life

Question 10

How do soils form?

Answer 10

From pedogenesis- a series of chemical, physical and biological weathering processes.

Question 11

What is the first step of pedogenesis?

Answer 11

Soil begins to form- we have water enter cracks (regolith) which causes physical and chemical weathering- can cause rust to form, can frost wedge and break down regolith more, can do dissolution, hydration and hydrolysis- forming new minerals along edges of cracks, and then as it moves downwards it transports minerals and ions it created/picked up.

Question 12

What is the second step in pedogenesis?

Answer 12

The nutrients released through chemical weathering in rock become food for bacteria, this bacteria produce co2 which combines with water in soil to make carbonic acid which further weather rocks. Then bacteria die and leave organic matter which supports plant growth.

Question 13

What is the the third step in pedogenesis?

Answer 13

Root wedging begins, bacteria fix nitrogen to support complex life, horizons begin to form.

Question 14

What is the fourth step of pedogenesis?

Answer 14

You get a well developed soil, with soil thickness increasing, parent material getting destroyed and fully formed horizons.

Question 15

What is a soil profile

Answer 15

Is all the horizons in a soil

Question 16

How are soil horizons named?

Answer 16

Named as O, A, B, C, R

Question 17

What is the oldest layer of soil?

Answer 17

As soil builds top down (cause weathering hits the surface before it trickles down) the oldest layer of soil is the highest one.

Question 18

Describe an O horizon

Answer 18

Is a soil horizon, has a lot of organic matter, makes carbonic acid through water seeping in it, forms coal

Question 19

What is humus

Answer 19

organic component of soil, formed by the decomposition of leaves and other plant material by soil microorganisms.

Question 20

Where do we see O horizons?

Answer 20

See this in bogs and swamps as we need a lot of water for organic matter to be preserved, only exists in a high oxygen environment.

Question 21

What is A horizon?

Answer 21

Is topsoil, consists of organic matter AND minerals (inorganic), the minerals in it are dissolved and removed by slight acidic water (carbonic acid) that was formed in O horizon.

Question 22

What is an E horizon?

Answer 22

Can be present sometimes, is a bleached horizon, is called the zone of eluviation because here water has leached out alot of the minerals and moved it downwards

Question 23

What is a B horizon?

Answer 23

Is the zone of illuvation (minerals are added from percolating mineral rich water that was above)- however this will be thin in saturated soils cause ions will tend to stay in solution.

Question 24

Why can there be multiple B horizons? Give examples of some

Answer 24

Because minerals accumulate at diff levels due to chnage sin density and composition, that’s why there may be B1, B2 or if we’re getting qualitative Bt- for clay, bk- for carbonate accumulation

Question 25

What is caliche?

Answer 25

Found in Bk layers, forms in dry environments, caco3 is picked up by water and is redeposited at deeper levels which can harden are impossible to dig through.

Question 26

What is a C horizon?

Answer 26

C horizon consists of pedogenically unaltered regolith, can transition into unweathered bedrock (R horizon).

Question 27

How do horizons form?

Answer 27

Through weathering, you initially get sediment and then through rain water you leech minerals and clay downwards until you deposit it as water drys up increasing the thickness of the b horizon and moving the C horizon downwards.

Question 28

In what climates will weathering occur and at what rates?

Answer 28

In hot humid climates weathering is fast, in hot dry climates weathering is slow, and in cold dry climates weathering is near impossible

Question 29

What is ‘Relief of the land” and how does it contribute to weathering?

Answer 29

As water flows downhill, flatter areas next to steep areas will have more chemical weathering as more water will infiltrate that regolith.

Question 30

How does surface area contribute to chemical weathering?

Answer 30

The more cracks in a rock the larger the surface area for water to attack, that’s why sediment weathers faster than big boulders.

Question 31

What wedges fastest, surfaces, corners, or edges?

Answer 31

Corners as weathering attacks three surfaces rather than 2 or 1.

Question 32

Explain how horizontal cracks form and how this can lead to soil formation

Answer 32

Horizontal cracks can form in rock by the rebound of earth that was previously under frost, rain water can travel through these cracks picking up minerals and concentrating them, producing regolith at sides of cracks and moving newly formed products lower creating thicker soils.

Question 33

Does composition of your parent rock affect chemical weathering?

Answer 33

Yes, bcuz some minerals are more susceptible to weathering such as olivine and pyroxene and ca rich plagioclase

Question 34

Why are olivine, pyroxene, and ca rich plagioclase more susceptible to weathering?

Answer 34

Because they form at high temps in deep earth and are not used to conditions at surface of earth.

Question 35

How does time affect chemical weathering?

Answer 35

The longer a rock is exposed,
the more it will be weathered
* Rates of chemical weathering
increase over time as surface
area increases

Question 36

What are two other ways (besides organic and inorganic) can soils be classified?

Answer 36

Can be classified as residual soils (meaning weathering that made it happened in one place no erosion) or transported soil (form on eroded materials)

Question 37

Which has an R horizon, residual soils or transported soils

Answer 37

residual soils have an R horizon as the weathering taking place making it was on that initial bedorck, transported soils don’t have an R horizon as the weathering taking place is on soils that came from another bedrock and are eroded.

Question 38

Name the four ways you can classify a transported soil

Answer 38

Alluvial soils: rivers
* Eolian soils: wind
* Glacial soils: glaciers
* Volcanic soils: volcanoes

Question 39

What soils are fertile?

Answer 39

Ones with increasing nutrients like N, P, K

Question 40

Name two really fertile soils and say why they’re fertile

Answer 40

Volcanic soils- tend to be fertile because volcanic ash is small and easily chemically weathered and also has a lot of nutrients and constant stream of it from volcanoes
Glacial soils- again because they were small and easy to weather and transported os have a variety of nutrients

Question 41

Define loess

Answer 41

windblown silt (small grains) from glacial deposits and deserts- very fertile as come from alot of diff environments and retain water well.

Question 42

What is a use for loess outside of agriculture?

Answer 42

Housing, as the material has clay which make sticky.

Question 43

What countries have the most loess?

Answer 43

China and Ukraine

Question 44

What are two more ways soils can be classified?

Answer 44

By color and texture

Question 45

What are some soil textures and what are they determined by?

Answer 45

Soil texture is determiend by grain size and crystal size as well as material (sand, silt, clay)
Coarse sandy soils will drain fast, clay soils will hold water long.

Question 46

What does the rate of soil drainage depend on?

Answer 46

Depends on comp of soil, how high water table is, and amount of rainfall

Question 47

Why is saturated soil bad? Whats the exception

Answer 47

Can water log crops, except for rice

Question 48

What does soil colour tell us about soils?

Answer 48

Dark brown/black soils- have high OM content- O horizon
Yellow- have an iron compound hydrated- soils have water- this is a poor drained soil, might have limonite
Grey-green- Fully saturated soil, waterlogged, iron reduced here and oxygen absent
Red- iron is oxidized (soil is well drained)

Question 49

try to memorize slide 45 if time

Question 50

When do soils pose problems?

Answer 50

When we want to build on them or clear them out for resources.

Question 51

What are vertisols?

Answer 51

Are a product of weathering, have a layered structure and abosrb water in these layers so they expand and decrease, NOT GOOD to build on- better luck bilding near rivers on transported sediment from water.

Question 52

What are Oxisols?

Answer 52

Is soil where minerals in it get leeched fast, leaving iron and aluminum so it’s red, leaf litter is only plants source of nutrition so deforestation is a big problem here, makes soil infertile.

Question 53

What happens when oxisols are exposed to sun due to deforestation?

Answer 53

They turn into rock hard ironstone, creates swamp

Question 54

What is permafrost?

Answer 54

describes soils
and surficial sediments that
are frozen for several years
at a time

Question 55

What is the active layer?

Answer 55

Is layer above permafrost that melts in summer and supports soil and plant growth

Question 56

Why is building on permafrost bad?

Answer 56

Cause it’ll freeze and expand or warm and contract creating unstable foundation.

Question 57

Why do you walk on grass when its raining instead of a mud path?

Answer 57

Because everyone’s walked on mud oath and have destroyed all the pore spaces in the soil meaning water will settle on top of it and not be drained.

Question 58

What are desert soils?

Answer 58

Are fragile and have thin crust of algae, bacteria, and lichen and stones to resist erosion and weathering- if removed desert soil erodes easily.

Question 59

Is soil a renewable resource?

Answer 59

Soil is continually formed, but its formation takes so long (hundreds to thousands
of years) that it is ~ a nonrenewable resource

Question 60

What’s sheet erosion

Answer 60

Water is removed in thin layers causes rill erosion- where small channels are formed which can turn into gullys when they get larger.

Question 61

How do we mitigate soil erosion?

Answer 61

Through terracing- making slopes into steps to avoid surface runoff and erosion as it’ll just accumulate on next step. Strip cropping (groundcover crops and widely spaced crops are sown in alternate strips) crop rotation 9to replenish nutrients and build symbiotic relationships w bacteria), and reducing tilling.