What is soil ?
Nature makes soil by placing many layers of organic material over rock, and having the microorganisms and other soil critters convert it into soil. Various species of plants grow and die and return to the soil, building fertility and complexity with each layer. As the soil improves, different plants grow until a desert becomes a forest. That’s all—just layers and layers and layers of organic matter. No digging, no testing, just organic matter continually breaking down into soil, which then feeds the next generation of plants. Soil organisms include the bacteria and fungi, protozoa and nematodes, mites, springtails, earthworms and other tiny creatures found in healthy soil. These organisms are essential for plant growth. They help convert organic matter and soil minerals into the vitamins, hormones, disease-suppressing compounds and nutrients that plants need to grow.
The power of one soil organism:
• Earthworms, are of vital importance in the development of productive soil. Their excrement is especially rich in N-P-K and calcium as well as microbes. Earthworm activity aerates drains and transports organic matter to the deep layers and in so doing brings micro-life to the lower levels of the soil. Healthy soil with its normal population of earthworms can produce from 10 to 90 tons of earthworm manure per hectare in a single year. Earthworm activated soil contains 3 to 4 times more available nutrients for plant life and can raise crop yields 35% or more. Without microbial life in the soil these small microbiological factories cease to exist.
• Bacteria are about 0.5 - 2µm in size, are very numerous in soil, and may be up to 6300 lb/acre. They are highly important in nitrogen fixation and as all-around support for fungi and actinomycetes due to their production of many organic acids from carbohydrates.
• Cyanobacteria, sometimes referred to as blue-green algae, are a somewhat special kind of microorganism; they fix nitrogen from the air unlike other algae. Cyanobacteria are more like bacteria than algae (based on cellular differences).
• Fungi are mycelia forming microorganisms. Their biomass may reach about 7200lb/acre. Unlike bacteria that ordinarily need easily decomposable organic substances, fungi also decompose complex hydrocarbon type molecules (lignin, tannin). They are relatively more advanced than bacteria. Fungi are important for humus formation and the aggregate structure of the soil. Mycelium binds soil particles and forms larger aggregates; it has been found that in a single gram of soil the length of the mycelium reaches 50 - 200m per gram (up to 7000ft/oz). Another important property of fungi is their mycorrhiza relationships with plant roots.
• Actinomycetes are microorganisms that fit between bacteria and fungi. They can utilize hard to decompose materials as fungi can, and some can fix nitrogen as bacteria do. Their biomass per hectare may reach that of bacteria 6300 lb/acre. Major genus of actinomycetes found in soils are the streptomycetes; these may make up to 70% of the actinomycetes’ biomass. Actinomycetes are very important for composting processes.
It is important to understand that the soil is a complex mixture of organisms; they are not separated in large groups or layers. Aerobes and anaerobes are mutually active and, indeed, dependent on each others’ products. There are many other organisms (which are over 30,000 species), that are important to soil function, like protozoas, which is a single cell animals.