5.1 Introduction to soil systems

Question 1

what is found in soil

Answer 1

organic matter, organisms, nutrients, minerals, air, water

Question 2

soil transfers

Answer 2

• Biological mixing: Organisms like earthworms move soil particles and organic matter.
• Leaching: Water-soluble substances move downward through the soil profile.

Question 3

soil profile order

Answer 3

O, A, E, B, C

Question 4

O horizon

Answer 4

Organic: the topmost layer, consisting of organic matter like leaf litter and decomposing organisms.

Question 5

A horizon

Answer 5

Also known as topsoil, rich in organic matter and minerals.

Question 6

E horizon

Answer 6

eluvial or leached horizon
- leaching removes material from the horizon

Question 7

B horizon

Answer 7

Subsoil, where materials leached from upper layers accumulate.

Question 8

C horizon

Answer 8

Partially weathered parent material.

Question 9

soil profile definition

Answer 9

a vertical section through a soil, from the surface down to the parent material, revealing the soil layers or horizons.

Question 10

inputs of soil

Answer 10

inputs: organic (i.e. leaf litter) and parent material (inorganic matter), precipitation, energy

Question 11

outputs of soil

Answer 11

• uptake by plants
• soil erosion
• energy

Question 12

transformations of soil

Answer 12

• decomposition (Rock weathering is a transformation process that breaks down rocks through physical or chemical means, releasing minerals into the soil and contributing to soil formation.)
• weathering
• nutrient cycling

Question 13

soil structure

Answer 13

the shape and arrangement of individual soil particles

Question 14

soil texture

Answer 14

the proportion of differently sized material - usually sand, silt, and clay - present in a soil

Question 15

sand particle size

Answer 15

less than 0.2mm in diameter

Question 16

silt particle size

Answer 16

less than 0.02mm

Question 17

clay particle size

Answer 17

less than 0.002mm

Question 18

clay characteristics

Answer 18

• Small particles (<0.002mm)
• Poor drainage
• Small air spaces
• High water-holding capacity
• High nutrient content

Question 19

sand characteristics

Answer 19

• Large particles (0.05-2mm)
• High drainage
• Large air spaces
• Low water-holding capacity
• Low nutrient content

Question 20

field capacity

Answer 20

the max amount of water that a soil can hold

Question 21

loam soil

Answer 21

• best soil for cultivation
• Balanced drainage
• Good water-holding capacity
• Adequate air spaces
• Moderate to high nutrient content
• size: mix of sand, slit and clay

Question 22

soil functions for humans

Answer 22

• medium for plant growth (most food for humans is grown in soil)
• soils contain an important store of relatively accessible freshwater (approx. 0.005% of global freshwater)
• soils filter materials added to the soil thereby maintaining water quality
• some recycling of nutrients takes place in soil → breakdown of dead organic matter
• provide raw materials in the form of peat, clays, sands, gravels, and minerals

Question 23

is fertile soil renewable or non-renewable?

Answer 23

non renewable because it takes so long to develop and because of the current rate of resource use compared to the length of time required for resources to be replaced

Question 24

soil forming processes involve

Answer 24

• gains and losses of material to and from the profile
• movement of water between the horizons
• chemical transformations within each horizon

Question 25

what kind of systems are soils

Answer 25

open system in a steady state equilibrium

Question 26

contrast in soils of tropical vs cold climates

Answer 26

tropical (Borneo): - extremely deep due to the warm, wet year-round climate cold (Iceland): - thin or non-existent due to the lack of chemical weathering

Question 27

physical conditions in soil that restrict root growth

Answer 27

- absence of cracks - shortage of oxygen due to waterlogging - dryness - temperatures that are too high or too low

Question 28

advantages of triangular graphs

Answer 28

- a large number of data can be shown on one graph - groupings are easily recognizable - dominant characteristics can be shown - classifications can be drawn up

Question 29

primary productivity of different soils

Answer 29

- sandy soil: low primary productivity due to poor water holding capacity and low nutrient status - clay soil: quite low primary productivity due to poor aeration and poor water infiltration - loam soil: high primary productivity due to medium infiltration rate, water holding capacity, nutrient status, aeration, and ease of working

Question 30

primary productivity of soil depends on :

Answer 30

- mineral content - drainage - water holding capacity - air spaces - biota - potential to hold organic matter

Question 31

Soil is an example of ...

Answer 31

non-renewable natural capital

Question 32

ratio air, water, etc .

Answer 32

Question 33

system definition

Answer 33

an assemblage of parts, working together, forming a functional whole

Question 34

a soil horizon

Answer 34

distinct layer within the soil profile

Question 35

chemical conditions in soil that restrict root growth

Answer 35

* high aluminium concentration, usually associated with low pH * low nutrient supply * chemicals toxic to plants (phytotoxic chemicals) in anaerobic soil (eg. saliniy associated with insecticides)

Question 36

disadvantages of triangular graphs

Answer 36

- difficult to interpret - easily get confused

Question 37

humus defintion ## Footnote not in syllabus, for own understanding

Answer 37

dark, organic material that forms in soil when plant and animal matter decays

Question 38

parent material definition ## Footnote not in syllabus, for own understanding

Answer 38

a weathered rock or deposit from and within which a soil has formed

Question 39

Explain the processes involved in the formation of fertile soils from bare rock. ## Footnote Exam-style question

Answer 39

1. Weathering of bare rock (physical, chemical, and biological) breaks it down into smaller mineral particles. 2. Pioneer species like lichens and mosses colonise the rock, helping to further break it down and begin soil development. 3. Organic matter accumulates as plants grow and die, adding humus and nutrients to the forming soil. 4. Soil horizons develop over time, allowing for nutrient cycling and water retention, creating a fertile soil capable of supporting more complex plant life.