This article from Penn University in the US, does a very good job of summarizing the positive effects of earthworm populations in agriculture, and also details how you can encourage the proliferation of earthworms in your area. It begins by stating that decades ago, very little attention was paid to the virtues of earthworms in the soil. However, as agriculture has begun to shift away from the input heavy conventional system, and more towards an understanding of natural soil fertility, the great importance of earthworms is coming into focus. Here are some of the benefits that the article focused on:
- Some species of worms create vertical burrows. These are like irrigation canals that help water to infiltrate deeply into the soil.
- Earthworms improve soil aeration, which is critical for plant root health. They do this in two ways: by creating burrows in the soil, and by aggregating the soil as they eat. Aggregation is the mixing of mineral soil and organic matter, creating stable soil structures. A healthy population of worms will process up to 10 percent of the topsoil every year.
- The effects above make soils much more resistant to compaction.
- Earthworms add stable organic matter to the soil. In the Netherlands, soil from the ocean and organic manure was used to establish a farm. Without earthworms the yields were very low. When earthworms were introduced the yields increased dramatically
- This is because organic matter processed by earthworms is immediately available to plants.
- They eat harmful nematodes, which can kill plant roots, and excrete beneficial microorganisms, which help feed plant roots.
- Earthworm castings are a neutral PH and help bring soil PH to ideal levels.
Types of Earthworms
There are three main classifications of earthworms, and all of them are important in soil health.
- Litter Dwellers / Epigeic Species- Not typically found in agricultural soils, they eat mostly plant residue and leaf litter, not soil. They can be encouraged by using healthy amounts of mulch.
- Topsoil Dwellers / Endogeic Species- They live in the upper 2-3 inchies of the soil, feeding on a mixture of soil, and organic matter that has been incorporated into it. They make burrows and fill these with aggregated soil.
- Subsoil Dwellers / Anecic Species – These species live in permanent burrows up to 6 feet deep. They come to the surface to find food (organic material and soil), which they bring down into the soil, and excrete in their burrows.
All worms have both male and female parts, however they need partners to reproduce. They produce cocoons with eggs inside them which are deposited along the burrows. Each worm can produce around 300 eggs a year, which take 1-5 months to hatch (this all varies depending on the species). Worms can take 3-12 months to reach sexual maturity, and they live for up to 10 years. It has been shown that earthworm populations, when given ideal conditions, can multiply by 20 (2000%) each year.
For earthworms to be healthy they need temperatures between 10-20 degrees Celcius. Exposure to 35 degrees will quickly kill them. This means that they will only thrive in well-covered soil, which allows the lower layers to remain cool.
They need loamy soil rich in organic matter to thrive. The soil must be moist, but well-draining, as worms will drown in waterlogged soil. I have personally experienced seeing millions of dead earthworms after a flood.
Finally of course they need food in the form of organic matter.
Agricultural Practices That Encourage Worms
The above conditions are rarely achieved in conventional systems which practice heavy tilling that destroys the soil structure and exposes the worms to high temperatures and regularly destroys their homes and populations. In addition to that, conventional systems rely heavily on synthetic fertilizer instead of organic matter, starving the worms, and toxic pesticides and herbicides which stress the worms.
Organic systems that use minimal tilling as well as methods that keep the soil moist and cool like cover cropping and mulching are very good at encouraging the growth of worm populations. Sustainable farming systems also rely heavily on adding organic matter to the soil which provides worms with food.
Any natural gardener or farmer worth their salt knows that worms are their best friend!
If you are just starting out, or converting your farm, it may help to cultivate some worms in a controlled environment. Get a starter culture by looking through a local dumpsite of organic matter (ask the gardener where he dumps all the leaves!) or by ordering from a supplier. You can set up a vermicompost bin where the worms can multiply safely. This will give you a supply of vermicasts, which are excellent fertilizers, and eventually worms you can introduce to your garden.
See the video below for an instructional video on making a vermicompost bin. This can be done even in a small apartment!