Lecture 4

Question 1

What are the 4 soil forming processes?

Answer 1

Transformations
Transfers
Additions
Losses

Question 2

How does soil organic matter change with depth?

Answer 2

Only a small quantity of SOM present as determined by weight (1-8% by weight in mineral topsoil)

Question 3

Soil development on residual material?

Answer 3

Highlighting the distinction between soil developed on residual and transported material

Soil developed on residual basalt bedrock

Question 4

Soil development on transport material?

Answer 4

Transport by:
Wind
Water

Soil developed on basal till (ice transported material)

Question 5

Define soil

Answer 5

Soil is the upper and biochemically whether portion of the regolith

Question 6

Define sediment

Answer 6

Sediment is material of varying size both mineral and organic that is being or has been moved from its state of origin by the action of wind water gravity or ice and comes to rest elsewhere on the surface

Question 7

List some transformations (internal change)

Answer 7

Physical and chemical weathering of minerals

Decomposition of organic matter

Waterlogging and gleying

Soil ripening

Question 8

List some transfers (internal rearrangement)

Answer 8

Pedoturbation

Infiltration and percolation

Eluviation / illuviation

Question 9

The development of soil profiles

Answer 9

Soils develop through a combination of additions, transformations, transfers and losses

Question 10

Physical weathering is the brittle fracture of rocks by the physical processes of…

Answer 10

A) unloading (removal reducing pressure on underlying rocks causing fractures to form eg granite or sandstone)

B) growth and expansion of ice (termed gelifraction) or salts (termed haloclasty) in rock pores and fissures

Question 11

When does chemical weathering occur?

Answer 11

When parent rock materials (primary minerals) react with acidic or oxidising substances, usually in the presence of water, to produce more stable secondary minerals

Question 12

Why are chemical weathering rates particularly high adjacent to plant roots?

Answer 12

Because of biological activity and CO2 production from respiration

Question 13

When are secondary minerals formed?

Answer 13

In weathering

They play critical roles in soils and ecosystem processes

Question 14

Define dissolution

Answer 14

The breakdown of minerals into component ions under the action of water

Question 15

Define hydration

Answer 15

Combination of a compound with water whereby the water is absorbed within the mineral lattice

Question 16

Define hydrolysis

Answer 16

The replacement of metal cations in minerals by a hydrogen ion from acidic soil water

Question 17

Waterlogging and gleying

Causes of saturation?

Answer 17

Rainfall (intensity and duration)
Rising water table
Overbank flooding

Question 18

What happens with waterlogging and gleying

Answer 18

Saturation slows down rate of organic matter decomposition

Gleyed soils are produced when waterlogging is intermittent or seasonal

Question 19

When does soil ripening occur

Answer 19

When a soil that is waterlogged or flooded dries out

Question 20

Transfers

Processes which can move material either physically or chemically within the soil, both upwards and downwards

Answer 20

Pedoturbation - physical mixing of soil profile eg soil creep

Bioturbarion - biological mixing of the soil by plants and animals

Question 21

Define cryoturbation

Answer 21

Physical mixing of the soil by frost

Question 22

Define the transfer of infiltration

Answer 22

Process by which water enters the soil and transports chemicals into the soil profile

Question 23

Transfers

Define eluviation

Answer 23

General term for the transfer of soil material in solution from one horizon, comprising 2 processes:

Leaching: movement of soluble organic and inorganic soil components in percolating water

Cheluviation: soluble organic complexes move metal cations through soil profile (especially iron and aluminium)

Question 24

Transfers

Define lessivage

Answer 24

Movement old clays in colloidal suspension without change in chemical composition

Produces soils such as acid brown earths

Question 25

Transfers

Define illuviation

Answer 25

Accumulation of materials in a lower B horizon after eluviation from A horizon

Question 26

Transfers: illuviation

How does material become deposited with a soil horizon?

Answer 26

1. Mechanical sieving effect
   Depends on pore size of transported material relative to pore space in the lower part of the profile
2. Chemical effect
   Reduced solubility and subsequent precipitation of colloidal and chelated material in the lower part of the profile

Question 27

What is pozolisation and example of?

Answer 27

Leaching, eluviation and illuviation

Question 28

Where can additions come from?

Answer 28

Outside or inside the ecosystem

Produced by outside:
Inflow of material from upslope
Aeolian input eg Iceland, tephra from volcanic ash

Produced by organisms from inside adding organic matter and nitrogen

Question 29

Losses

Answer 29

Wind erosion

Rain erosion

Question 30

What is the effect of climate on soil depth?

Answer 30

Increased temperatures and moisture availability together enhance weathering

Increased weathering leads to an increase in the depth of soil

Question 31

Soil catena and topography

Answer 31

Predictable series of soils arranges down a slope due to the differences in moisture, erosion and sediment transport along with pedogenic processes

Question 32

Effects of vegetation type on soil development?

Answer 32

A) ultisol development: forests
Soil with low base status and clay enriched subsoil
Red colour due to iron oxides

B) mollisol
Development: grasslands
Very fertile soil with organic matter

Question 33

Organic soils: HISTOSOLS

Answer 33

Consist of organic debris which accumulated at the surface under wet or dry conditions