Be a Better Farmer: Understand
the Living Soil
Part 4 - Those Wonderful Worms
Originally Printed in Country Guide, Spring 2001
Table of Contents
- Introduction
- Earthworm Species and Habitat
- Influencing Earthworm Populations
- Three Facts From the World of Worms
- Related Links
Introduction
Earthworms don't just improve soil texture. They also tell you a lot
about the quality of your soil management.
Earthworms are the most easily recognized soil organism. Farmers and
gardeners have long viewed them as a sign of soil health. New no-tillers
eagerly document the increase in worm numbers as a sign of improving soil
health -- and they are right to make that assumption. In fact, worms are
often studied as an "indicator species" for monitoring changes
in soil quality.
As farmers, we can learn a lot about our soils by monitoring worm populations.
There is also a soil management angle. Many activities that affect earthworms
also affect other soil organisms. Because of their size, however, worms
are easy to study and monitor. Let's take a closer look at the mighty
earthworm.
Earthworm Species and Habitat
There are thousands of earthworm species in the world but only about
20 in Canada. Those we find across Canada (except in a small area on Vancouver
Island) are not native. The original earthworms were wiped out by glacial
ice sheets that covered Canada until about 15,000 years ago, Canadian
earthworms are immigrants, carried here from Europe by the early settlers
on root stocks and in the earthen ballast of ships.
Earthworms are most numerous in fine and medium textured soils (clays
and loams). They are less common in sands, gravels and acidic soils. Earthworms
breathe through their skin and need to keep it moist to stay alive. Soils
that are dry for prolonged periods tend to desiccate worms.
Two types of worm are found in agricultural soils in Canada. First is
the deep burrower, Lumbricus terrestris. Commonly called nightcrawlers
or dew worms, these are the worms most commonly sold for fish bait. Adults
are generally 10 to 30 cm long. They create large vertical, permanent
burrows up to 2 meters deep in the soil profile. They pull surface plant
residues, and in some cases living plant material, down into the mouth
of the burrow to soften and be eaten.
In fields with enough surface residue, you will see the middens (a mixture
of plant residues, worm droppings, small stones) that these worms build
over the mouths of their burrows. These little piles protect the burrow
and also serve as a food reserve.
Nightcrawler populations are heavily influenced by tillage and rotations
that reduce surface residue levels. Tillage can disturb eggs laid on the
soil surface, damage burrows and injure the worms. If you want nightcrawlers,
leave some crop residue. It's necessary for both food and protection.
Shallow-dwelling worms also inhabit cropland. Many of these smaller species
live in the top 10 to 30 cm of soil. Adults vary in length from less than
20 mm to greater than 15 cm. These earthworms do not build permanent burrows,
but travel randomly through soil. They are also affected by tillage in
that any reduction in residue reduces populations. Growing crops and crop
residues provide food and protect the soil from dramatic moisture and
temperature changes that reduce worm populations.
Influencing Earthworm Populations
Together with other organisms that cycle soil nutrients
and stabilize soil structure, earthworms contribute to soil health. Examining
the response of worm populations to farm practices can tell us how these
practices influence other soil life.
Worms mix soil and crop residues, promoting the breakdown of organic
matter and the cycling of nutrients. They leave nutrient-rich casts behind,
coating the walls of their burrows. Plant roots often grow along or through
worm burrows, taking advantage of the better soil structure, higher nutrient
levels, and ease of root expansion along the channel.
Burrowing increases soil porosity, promoting movement of air and water.
Macropores formed by nightcrawler channels enhance drainage. When improved
drainage is seen early in the adoption of no-till, these vertical worm
channels are responsible.
Earthworms have a lot of predators - birds, raccoons, other small animals,
and a variety of insect pests including the cluster fly. A common pest
in old farm houses, cluster flies reproduce by laying their eggs on a
particular species of earthworm.
Human activities, however, have the greatest impact on worm populations.
Earthmoving for building houses and large-scale soil disruption has the
greatest effect, followed closely by intensive tillage practices and poor
crop rotations. Pesticides application does not usually affect worm populations.
It pays to encourage large and varied worm populations in your soil.
Some people talk about seeding fields with earthworm eggs but improved
cultural practices work better. If the food source and habitat aren't
there, worms will not grow and reproduce.
To boost the worm population on your farm, reduce tillage or go to no-till;
use a varied crop rotation that includes forages and cereal grains; apply
manure or maintain surface crop residues; and plant cover crops.
Three Facts From the World of Worms
- Worm picking for the U.S. bait market is big business. Most fields
with worm populations high enough to interest pickers (no-till fields,
hay, pasture, turf) can sustain limited picking with little or no ill
effect. Be careful when making a contract with pickers. For more information
on worm picking, check out the Ag Canada web site http://res2.agr.gc.ca/london/faq/earth-terre_e.htm.
- Seagulls are often blamed for high worm losses after plowing. But
it's the plow, not bird feeding that does the most damage. Seagulls
eat worms and other disturbed soil life that the plow has injured or
exposed.
- Application of anhydrous ammonia and soil fumigants does kill worms
in the sterilized soil band. Usually the impact is short-lived as populations
are replenished from surrounding soil. Caution: repopulation may not
happen if rotation and tillage practices do not support worms.
Related Links
