If you want to make your soil better, you need to start with earthworms.
Healthy soils have strong earthworm populations and you can gauge their numbers by the presence of middens, little piles of residue, says Quebec researcher Odette Menard.
“When I see a lot of middens, I know it’s a healthy field. If I see residue accumulation, I know there’s a hole at the end of it and there are earthworms underneath.”
There are three different kinds of earthworms: epigeic, endogeic, and anecic.
Epigeic are small earthworms that work fresh organic material in the first few inches of soil. They are short lived and reproduce within 90 to 150 days.
Endogeic are large and dark and take the residue from the top of the soil and move it through soil profiles. They also take care of decaying roots. These earthworms stay inside the soil and reproduce around 150 days.
Most people are more familiar with anecic earthworms, which are big and build vertical tunnels in the soil. In Quebec, these earthworms can live up to eight years, but take more than 400 days to reproduce.
“If you get into no till and you don’t have a basic population to begin with, it will take time to get there,” said Menard.
Anecic earthworms, which can breath through their skin, are the ones that will be seen on the soil surface or on the sidewalk on a rainy day.
“When it is raining, the humidity is right outside, so they go out until the sun comes around. They can go about 12 to 15 feet away from their holes. If they go farther than that, they can’t find their way back home, because they are blind.”
But it’s their work down below that benefits your farm.
Earthworm tunnels, which can last for up to 30 years, aerate the soil and provide pathways for roots. Their manure is powerful stuff, and a tonne of earthworms can produce two-thirds of an inch of manure across an entire acre in a year, which is a lot of nitrogen. And when they consume microbes, the little critters flourish in the warmth and humidity of an earthworm’s digestive tube and reproduce.
But they need healthy soil to prosper.
“Earthworms will be in a field if they have food,” said Menard. “No food, no earthworms.”
Research has found earthworm populations can increase by 60 per cent when there is 30 per cent residue in sandy soil. Clay soils show an even more drastic increase, with earthworm populations jumping by 150 per cent when there is 30 per cent residue. Good rotations also have a huge impact on earthworm populations in both clay and sandy soils, causing populations to jump by 255 per cent.
“The healthier your soil is, the more efficient the nutrient availability will be and then the earthworm population will be even better,” said Menard.
Tilling, on the other hand, reduces their population because it increases soil temperature, reduces moisture, and speeds residue breakdown.