W5 - Topic 9 - Soil Organisms and Organic Matter Flashcards
What is the approximate weight of microorganisms and worms in healthy soil?
Approximately 2 kg of microorganisms and 0.5 kg of worms per barrow and a half of fertile soil
What are the influences of soil organisms?
- Soil formation
- Soil structure improvement
- Nutrient cycling for plants
How many organisms can be found in 1 kg of soil?
Up to 2 trillion organisms
What is the concentration of microbes beneath 1 square meter of soil surface?
36,500,000 microbes
Define macrofauna in soil organisms.
Larger organisms that burrow and tunnel
Give examples of macrofauna.
- Rabbits
- Wombats
- Ants
- Worms
Define mesofauna in soil organisms.
Medium-sized organisms that move through larger soil pores
What are microfauna?
Small organisms that move through soil pores
List examples of microfauna.
- Mites
- Protozoa
- Nematodes
What is microflora?
Relatively immobile microorganisms
List examples of microflora.
- Algae
- Fungi
- Actinomycetes
- Bacteria
What functions do earthworms serve in soil?
- 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
What conditions do earthworms thrive in?
- Organic matter high in protein
- Adequate water and air
- Low temperature fluctuations
- pH 5-7.5
- Absence of pesticides
What role do algae play in soil?
- Add organic matter to soil
- Some fix atmospheric nitrogen
What are the requirements for algae growth?
- Sunlight
- Water
- High pH (7.5-8)
Describe the structure of fungi in soil.
Appear as white thread-like structures (hyphae) forming a network (mycelium)
What do fungi break down?
Tough organic materials (cellulose and lignin)
What is the function of mycorrhizal associations?
Form symbiotic relationships with plant roots
What is the scale of fungal hyphae in soil?
1 gram of soil may contain 100 meters of fungal hyphae
What are actinomycetes?
Intermediates between fungi and bacteria present in huge numbers but grow slowly
What do actinomycetes break down?
Resistant organic matter after initial decomposition by fungi and bacteria
What functions do bacteria serve in soil?
- Break down organic matter
- Oxidize minerals
- Fix nitrogen
What is the rhizosphere?
Area closest to plant roots with a high concentration of microorganisms
What do plants release into the rhizosphere?
- Sloughed cell wall fragments
- Root exudates
- Leaky cell contents
- Dead cells and roots
What is nitrogen fixation?
Process where Rhizobium bacteria form nodules on legume plants and convert atmospheric nitrogen into plant-available compounds
Give examples of legume plants involved in nitrogen fixation.
- Acacias
- Rye
- Lupin
- Pea
What are the two types of soil colloids?
- Organic colloids
- Inorganic colloids
What are the properties of soil colloids?
- Very small, stay suspended in solution
- Carry electrical charge
- Attract and hold cations
What are the two types of organic matter?
- Anything that is or was once living
- Humus
What is humus?
End product of organic matter decomposition by microbes
What are the functions of humus?
- Stores and supplies slow-release nutrients
- Binds soil particles together for improved structure
- Resistant to decomposition
- Gives soil its earthy brown color and aroma
What factors affect organic matter content in soil?
- Clay content
- Environmental conditions
- Cultivation
What is the average organic matter content in Australian soils?
3-5%
What is the carbon cycle?
Continuous recycling of carbon through plants, animals, decomposition, soil organic matter, and atmospheric CO₂
What are the beneficial effects of organic matter?
- Improves soil structure
- Enhances nutrient storage
- Provides nutrients
- Supports beneficial organisms
- Reduces soil compaction
What are potential problems associated with organic matter?
- Phytotoxins from fresh organic waste
- Introduction of pathogens
- Weed seeds in incompletely composted material
- Reduced water infiltration
- Nitrogen drawdown
What methods can be used to add organic matter to soil?
- Compost/soil conditioners
- Manure
- Mulch
- Green manure
What are the characteristics of compost/soil conditioners?
- Mainly fibrous material
- Low in nutrients
- Used for improving existing soils
What is green manure?
Growing plants specifically to dig into soil as organic matter
What are the seasonal options for green manure?
- 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
What are the benefits of mulches?
- Soil insulation
- Reduced evaporation
- Erosion prevention
- Improved water infiltration
- Weed suppression
What are the types of decomposition in composting?
- Aerobic (with oxygen)
- Anaerobic (without oxygen)
What are the advantages of aerobic decomposition?
- No bad smell
- Low phytotoxicity
- High heat generation
What are the disadvantages of anaerobic decomposition?
- Strong odors
- Higher phytotoxicity
- Slower elimination of pathogens
List green materials suitable for composting.
- Grass clippings
- Coffee grounds/tea bags
- Vegetable/fruit scraps
- Plant trimmings
- Non-seeding weeds
- Eggshells
- Animal manures
- Seaweed
List brown materials suitable for composting.
- Fallen leaves
- Pine needles
- Twigs
- Straw or hay
- Sawdust
- Corn stalks
- Paper
- Cotton fabric
- Cardboard
What is the ideal C:N ratio for effective composting?
30:1
What is a holistic soil health approach?
Successful plant growth depends on soil health, not just direct feeding
What is the relationship between soil and plants?
Soil feeds organisms, which release nutrients for plant uptake
True or False: Happy soil equals happy plants.
True
