By Jon Cloud

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. To a large extent our topsoils in Ontario have been made by earthworms during the last 150 years. Before that, there were no earthworms in Eastern Canada.;

In an acre of healthy soil, there will be from three to five different species (19 varieties can be found in Ontario alone) which burrow horizontally or vertically as they feed. They provide 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 the cracks, fissures, and channels created by earthworms and 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%. Less fertilizer leaches as the burrows allow crop roots to reach deeper into the soil and to intercept nutrients that might otherwise escape.;

Earthworms plough close to home, depositing large amounts of soil on the surface in their castings. A healthy soil may contain tons of castings per acre. The casting contributes five times more available nitrogen, seven times more available phosphorous and 11 times more exchangeable magnesium than the soil the earthworm ingested.;

The castings have much greater productive value for plant growth than other soil because the nutritional elements have been concentrated in them in water soluble form and in a more balanced condition. The castings produce a topsoil that is practically neutral, with increased organic content; they favor bacterial multiplication and functioning, decompose vegetable matter and greatly enhance productive value of the soil. In its passage through the worm, the mineral subsoil undergoes chemical changes making it immediately available for plant nutrition. ;

Earthworms vary in their habitats and food requirements. Some require high carbon content like that found in manure or muck. Some make vertical tunnels a metre deep.;

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, six to eight inches down and 12 inches square. Check your results against fields which you have winter cover cropped or where you have worked 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 favorable, earthworms can be inoculated into the soil. However, simply "seeding" them is not 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 waste, stubble, dead vegetable, manures, dead animal residues – constitute the cheap and ever-renewed source of earthworm food for soil building. Worms like the shaded conditions of a cover crop or sod field to keep the residue moist. ;