Soil Composition
Living Matter
Mostly in the top 4" of the soil.
Good guys & bad guys...but large volume & diversity control the trouble makers by making it a competive environment for resources.
1 teaspoon of soil:
- 1 billion bacteria
- several yards of fungal hyphae
- several thousand protozoa
- few dozen nematodes
Bacteria
attracted by the root exudate (carbohydrates and proteins secreted from the plant roots).
the numbers and kinds of bacteria that are attracted are controlled by the plant, depending on season and conditions
most bacteria need carbon sources to live. Carbon sources include plants, waste products from insects & mammals, and bodies of these organisms. by consuming these sources, they immobilize nutrients and become little bags of fertilizer (think time-release). they release nutrients in plant-available form when they are in the rhizosphere.
bacteria use slime to stick to substrates and move around. this slime traps pathogens. this slime is also responsible for sticking soil particles together, giving soil its structure.
vitmamins and antiobiotics are produced by some bacteria & fungi that help the plants
bacteria also work in th ephyllosphere (leaf surface)
Fungi
attracted by the root exudate (carbohydrates and proteins secreted from the plant roots).
the numbers and kinds of fungi that are attracted are controlled by the plant, depending on season and conditions
fungal hyphae kill nematodes, which are after the plant roots
plants attract fungus to their roots for protection by secreting exudate from their roots into the rhizosphere. The rhizosphere is the zone immediately surrounding a root by about 1 mm (1/25").
mycorrhizal fungi provide water & phosphorous, as well as other nutrients to the plant in return for the plant's exudate that it lives off of.
nets & webs formed by fungi around the roots act as physical barriers to pathogens
vitmamins and antiobiotics are produced by some bacteria & fungi that help the plants
immobilize nutrients and become little bags of fertilizer (think time-release). they release nutrients in plant-available form when they are in the rhizosphere.
chemical fertilizers (salts) kill these fungi
fungal hyphae travel through the soil particles, binding them toghether thread-like into aggregates, giving soil structure
Protozoa
include amoebae, paramecia, flagellates, and ciliates.
eat bacteria then excrete wastes for roots to uptake
Nematodes
Insects: centipedes, springtails, ants, ladybug larvae
earthworms
~50 earthworms per square foot
burrow through soil, giving pathways for air & water to enter & leave the soil.
slugs & snails
Organic-nonliving Matter
Inorganic
Soil Structure
Bacterial slime binds soil particles together
fungal hyphae thread together particle aggregates
worms, insect larvae & moles move throught the soil in search of food and protection which create pathways that allow air & water to enter & leave the soil
