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Giants Of The Soil

By Jon Cloud

Soy City Foods, 2847 Dundas St. W., Toronto, M6P 1Y6

Earthworms are one of the great soil building forces of the universe. They eat the soil, digest it, and condition it. Aristotle called them "the intestines of the soil". Earthworms have contributed immensely to the topsoils in Ontario during the last 150 years. Before that, there were no earthworms in Eastern Canada.

In Ontario there are 19 different varieties of earthworms. These vary in their requirements for habitat and food. Some require high carbon content like that found in manure or muck. Some make tunnels a metre deep vertically. In any given acre of healthy soil, there will be between three to five different species. These burrow horizontally or vertically as they feed. This provides a natural drainage system which can soak up great amounts of rainfall.

According to Bruce Bowman of Agriculture Canada's London Research Centre, water can flow rapidly through cracks, fissures or channels created by earthworms or decaying roots. Such pores can account for up to 90% of the water conducted through a soil profile during times of intense rainfall. These burrows also let in more oxygen to speed decomposition of plant residues and enhance uptake of potassium. The aerating tunnels increase the air capacity in the soil by 60 to 75%. There is less fertilizer leaching. The burrows allow crop roots to reach deeper into the soil and to intercept nutrients that might otherwise escape.

Earthworms plow close to home, depositing tons of soil on the surface in their castings. A healthy soil may contain tons of castings per acre. The castings can contributes five times more available nitrogen, seven times more available phosphorus, and eleven times more exchangeable magnesium than the soil the earthworm ingested.

Castings greatly improve a soil's productive value for plant growth. This is due to the fact that the nutritional elements have been chemically altered into a water soluble form, and into a more balanced condition. The castings produce a topsoil that is practically neutral in pH, has increased organic content, and favours bacterial multiplication and functioning for the decomposition of vegetable matter. It has been observed that fruit trees establish more readily around them.

To gain the benefits of a good earthworm population you need eight to ten earthworms per square foot, six to eight inches deep. Take a shovel and dig some samples at half a dozen test sites per field. Select some which have had a winter cover or where you have worker green manure into the soil. These samples should show you the advantage of cover cropping and green manure to increase your earthworm population.

If no worms are present but conditions are favourable, earthworms can be inoculated into the soil. However, simply "seeding" them in isn't enough. The worms need to find the right conditions. They require an environment with lots of crop residue and a calcium-rich soil. All the biological end products of life: kitchen and farm wastes, stubble, dead vegetables, manures, dead animals residues, etc. constitute the cheap and ever-renewed source of earthworm food for soil-building. They like the shaded conditions of a cover crop or sod field to keep the residue moist. To provide winter cover, Bill Becker research director of Agricultural Research Farms in Illinois, suggests seeding oats after a soybean harvest. He also recommends you disk in a crop like hairy vetch before planting in the spring, if your earthworm population isn't high enough to ensure meeting all your nitrogen needs. We recommend that you consider oil radish after soybeans because the oil radish is frost tolerant, but winter kills and therefore incorporates readily into the soil in spring. In either case, there is no excuse for "starving your workers". The earthworm is one of the hardest workers on an organic farm, and everyone knows that you have to feed your help if you expect them to stay around.

Copyright 1995 Ecological Farmers Association of Ontario. Reprinted with permission. All rights reserved.


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