W5 - Topic 9 - Soil Organisms and Organic Matter

Question 1

What is the approximate weight of microorganisms and worms in healthy soil?

Answer 1

Approximately 2 kg of microorganisms and 0.5 kg of worms per barrow and a half of fertile soil

Question 2

What are the influences of soil organisms?

Answer 2

• Soil formation
• Soil structure improvement
• Nutrient cycling for plants

Question 3

How many organisms can be found in 1 kg of soil?

Answer 3

Up to 2 trillion organisms

Question 4

What is the concentration of microbes beneath 1 square meter of soil surface?

Answer 4

36,500,000 microbes

Question 5

Define macrofauna in soil organisms.

Answer 5

Larger organisms that burrow and tunnel

Question 6

Give examples of macrofauna.

Answer 6

• Rabbits
• Wombats
• Ants
• Worms

Question 7

Define mesofauna in soil organisms.

Answer 7

Medium-sized organisms that move through larger soil pores

Question 8

What are microfauna?

Answer 8

Small organisms that move through soil pores

Question 9

List examples of microfauna.

Answer 9

• Mites
• Protozoa
• Nematodes

Question 10

What is microflora?

Answer 10

Relatively immobile microorganisms

Question 11

List examples of microflora.

Answer 11

• Algae
• Fungi
• Actinomycetes
• Bacteria

Question 12

What functions do earthworms serve in soil?

Answer 12

• Create tunnels for water and air movement
• Break down soil and organic matter to release nutrients
• Improve soil structure through ‘clay-humus complexing’
• Produce vermicasts that cement soil particles together
• Mix soil through their movement

Question 13

What conditions do earthworms thrive in?

Answer 13

• Organic matter high in protein
• Adequate water and air
• Low temperature fluctuations
• pH 5-7.5
• Absence of pesticides

Question 14

What role do algae play in soil?

Answer 14

• Add organic matter to soil
• Some fix atmospheric nitrogen

Question 15

What are the requirements for algae growth?

Answer 15

• Sunlight
• Water
• High pH (7.5-8)

Question 16

Describe the structure of fungi in soil.

Answer 16

Appear as white thread-like structures (hyphae) forming a network (mycelium)

Question 17

What do fungi break down?

Answer 17

Tough organic materials (cellulose and lignin)

Question 18

What is the function of mycorrhizal associations?

Answer 18

Form symbiotic relationships with plant roots

Question 19

What is the scale of fungal hyphae in soil?

Answer 19

1 gram of soil may contain 100 meters of fungal hyphae

Question 20

What are actinomycetes?

Answer 20

Intermediates between fungi and bacteria present in huge numbers but grow slowly

Question 21

What do actinomycetes break down?

Answer 21

Resistant organic matter after initial decomposition by fungi and bacteria

Question 22

What functions do bacteria serve in soil?

Answer 22

• Break down organic matter
• Oxidize minerals
• Fix nitrogen

Question 23

What is the rhizosphere?

Answer 23

Area closest to plant roots with a high concentration of microorganisms

Question 24

What do plants release into the rhizosphere?

Answer 24

• Sloughed cell wall fragments
• Root exudates
• Leaky cell contents
• Dead cells and roots

Question 25

What is nitrogen fixation?

Answer 25

Process where Rhizobium bacteria form nodules on legume plants and convert atmospheric nitrogen into plant-available compounds

Question 26

Give examples of legume plants involved in nitrogen fixation.

Answer 26

* Acacias * Rye * Lupin * Pea

Question 27

What are the two types of soil colloids?

Answer 27

* Organic colloids * Inorganic colloids

Question 28

What are the properties of soil colloids?

Answer 28

* Very small, stay suspended in solution * Carry electrical charge * Attract and hold cations

Question 29

What are the two types of organic matter?

Answer 29

* Anything that is or was once living * Humus

Question 30

What is humus?

Answer 30

End product of organic matter decomposition by microbes

Question 31

What are the functions of humus?

Answer 31

* Stores and supplies slow-release nutrients * Binds soil particles together for improved structure * Resistant to decomposition * Gives soil its earthy brown color and aroma

Question 32

What factors affect organic matter content in soil?

Answer 32

* Clay content * Environmental conditions * Cultivation

Question 33

What is the average organic matter content in Australian soils?

Answer 33

3-5%

Question 34

What is the carbon cycle?

Answer 34

Continuous recycling of carbon through plants, animals, decomposition, soil organic matter, and atmospheric CO₂

Question 35

What are the beneficial effects of organic matter?

Answer 35

* Improves soil structure * Enhances nutrient storage * Provides nutrients * Supports beneficial organisms * Reduces soil compaction

Question 36

What are potential problems associated with organic matter?

Answer 36

* Phytotoxins from fresh organic waste * Introduction of pathogens * Weed seeds in incompletely composted material * Reduced water infiltration * Nitrogen drawdown

Question 37

What methods can be used to add organic matter to soil?

Answer 37

* Compost/soil conditioners * Manure * Mulch * Green manure

Question 38

What are the characteristics of compost/soil conditioners?

Answer 38

* Mainly fibrous material * Low in nutrients * Used for improving existing soils

Question 39

What is green manure?

Answer 39

Growing plants specifically to dig into soil as organic matter

Question 40

What are the seasonal options for green manure?

Answer 40

* Cool/cold season crops: Fava beans, broad beans, tick beans, fenugreek, lupins, oats, subclover, vetch, ryecorn, mustard, brassicas, wheat, barley * Warm season crops: Buckwheat, cowpea, millet, lablab, marigolds, mung bean, soybean

Question 41

What are the benefits of mulches?

Answer 41

* Soil insulation * Reduced evaporation * Erosion prevention * Improved water infiltration * Weed suppression

Question 42

What are the types of decomposition in composting?

Answer 42

* Aerobic (with oxygen) * Anaerobic (without oxygen)

Question 43

What are the advantages of aerobic decomposition?

Answer 43

* No bad smell * Low phytotoxicity * High heat generation

Question 44

What are the disadvantages of anaerobic decomposition?

Answer 44

* Strong odors * Higher phytotoxicity * Slower elimination of pathogens

Question 45

List green materials suitable for composting.

Answer 45

* Grass clippings * Coffee grounds/tea bags * Vegetable/fruit scraps * Plant trimmings * Non-seeding weeds * Eggshells * Animal manures * Seaweed

Question 46

List brown materials suitable for composting.

Answer 46

* Fallen leaves * Pine needles * Twigs * Straw or hay * Sawdust * Corn stalks * Paper * Cotton fabric * Cardboard

Question 47

What is the ideal C:N ratio for effective composting?

Answer 47

30:1

Question 48

What is a holistic soil health approach?

Answer 48

Successful plant growth depends on soil health, not just direct feeding

Question 49

What is the relationship between soil and plants?

Answer 49

Soil feeds organisms, which release nutrients for plant uptake

Question 50

True or False: Happy soil equals happy plants.

Answer 50

True