| 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. |
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Because of the vital role they play in plants growth, one of the
measures of soil quality is abundance of living organisms. |
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Indiscriminate use of fertilizers, both chemical and animal manures, can
result in a decline in the numbers of beneficial organisms in the soil.
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| 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. |
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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. |
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| 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. |
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| 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. |
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Protozoa mainly feed on bacteria and release nitrogen and other nutrients
in their waste.
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| 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. |
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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. |
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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. |
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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. |
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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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