Earth friendly gardening in the Kootenays region of British Columbia, Canada

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Soil Organisms

A fertile soil teems with millions of living organisms, from microscopic, such as bacteria and protozoa, to large such as worms and arthropods (ants, springtails, sowbugs (woodlice), spiders, mites, centipedes, millipedes, etc.) These organisms, in the course of their life modify and improve the structure, availability of nutrients, and chemical condition of soil.
Because of the vital role they play in plants growth, one of the measures of soil quality is abundance of living organisms.

Indiscriminate use of fertilizers, both chemical and animal manures, can result in a decline in the numbers of beneficial organisms in the soil.

Larger soil organisms help in decomposition of plants residue and other organic matter in the soil. Arthropods shred organic matter into small pieces. Earthworms and arthropods stir up and churn the soil. By leaving numerous channels, they also help making soil porous.
Microorganisms feed on the decomposed organic matter transforming it into plant nutrients, gases and sticky substances that help granulate soil particles, making soil porous and easy to penetrate by air and water.
Another decomposers of organic materials are the soil fungi. Fungi are tolerant of acid soil conditions. Some fungi help decompose dead organic material such as leaves. Other kinds of fungi live as partners with plants. They provide mineral nutrients to the plant in exchange for carbohydrates and other chemical compounds they cannot make themselves.
The most abundant organisms in the soil are bacteria and protozoa. They are minuscule, one-celled organisms that can only be seen with a microscope. They obtain their food by decomposing more complex organic substances into simple ones, such as carbon dioxide, water, and ammonia. Still other bacteria transform ammonia into nitrate salts, the only form in which most plants can use nitrogen.
Some kinds of bacteria may form modules on the roots of some plants and convert atmospheric nitrogen into nitrogen compounds available to the plant.

Protozoa mainly feed on bacteria and release nitrogen and other nutrients in their waste.

Another kind of soil organisms, nematodes, look like transparent, thread-like, microscopic worms. They are common in soils everywhere. Some kinds of nematodes feed on bacteria and fungi. Other kinds feed on decaying plant material.
As is the case with other soil organisms, not all kinds of nematodes are beneficial. Certain kinds can cause significant damage by infecting plant roots.
Best known to gardeners are harmful to plants root-knot nematodes. Because of their wide host range and widespread distribution, they often cause significant reduction in both, yield and quality of crops. Nematode infestations can be identified by yellowing and stunted plants.

After reading the short introduction above you may want to learn more about the soil organisms and their impact on the plant life. Below are links to the sites with great information on the topic.

The Key to Healthy Soil   When we are standing on the ground, we are really standing on the roof-top of another world. Living in the soil are plant roots, viruses, bacteria, fungi, algae, protozoa, mites, nematodes, worms, ants, maggots and other insects and insect larvae (grubs), and larger animals. Indeed, the volume of living organisms below ground is often far greater than that above ground. Washington State University website.
Soil Biology   As individual plants and soil organisms work to survive, they depend on interactions with each other. By-products from growing roots and plant residue feed soil organisms. In turn, soil organisms support plant health as they decompose organic matter, cycle nutrients, enhance soil structure, and control the populations of soil organisms including crop pests.  US Department of Agriculture, Natural Resources Conservation Service website.

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