Earthworms provide numerous benefits to soil. One of the under-researched side effects of our switch to zero till may be an increase in earthworm activity
When I taught the first year soils class at the University of Saskatchewan, soil biology was a quick study. The rhizobium that fix nitrogen with legumes were discussed in detail. The bacteria that control conversion of organic nitrogen to the mineral forms (nitrate and ammonium) were also considered important.
The bigger things like earthworms were mentioned in passing and identified as Lumbricus terrestris. It was all academic, as we did not have any earthworms in field soils on the Canadian Prairies at that time. On soil surveys, we dug thousands of holes in farm fields each year and rarely turned up an earthworm.
But with the change to continuous cropping and zero till farming, that has all changed. My Dundurn farm has been continuous crop min/zero till for about 15 years. The past few years I have been finding earthworms when checking seeding depth. So this summer I dug around like a pocket gopher and read several books and research papers from the library.
In today’s world, information is easy to come by. Dr. Sina Adl, our new head of Soil Science at the U of S, is a soil ecologist. He alerted me to the first book written about earthworms. It was written in 1881 by none other than the famous Charles Darwin of Beagle, Galapagos Islands and On the Origin of Species fame. A few mouse clicks later and I had a copy of the book on my computer desktop. It runs to seven chapters and 342 pages. His observations, mainly from England, showed the beneficial actions of earthworms in forming topsoil, aiding soil structure and promoting drainage through the burrows of the worms. He had several hand sketched cross sections showing the topsoil created by earthworms and the stones that were buried by the new topsoil. He called it “vegetable mould.”
It turns out there are hundreds of species of earthworms. In terms of habits they can be placed in three groups:
1. Surface Feeders: These feed on the soil surface — on leaves and other plant materials — and are found under fallen trees and similar places. Their casts (feces) form part of the surface soil.
2. Deep drillers: These produce single burrows from the soil surface to depths of two meters or more. They consume surface litter and mix it with soil, and can bring subsoil to near surface. Lumcricus terrestris is a deep driller.
3. Topsoil dwellers: These worms work in the topsoil (about 6 inch depths) and produce roughly horizontal burrows. They live off surface litter and mix it with soil.
Biologists have fancy names for these three groups (Epigeic, Anecic and Endogeic respectively), but my names are easier to remember.
From my observations the main actors in our fields are from the third group — Topsoil Dwellers.
Earthworms are well known to improve soil structure, drainage and general physical health. Through defecation and secretion and the recycling of dead earthworms, they contribute to nitrogen and phosphorus fertility. Earthworms are about 60 per cent protein, so a lot of nitrogen is supplied by dead earthworms.
It is well known that Canadian Prairie farmers have improved the soil in the past 20 years through continuous cropping, good fertilization and crop rotation. We must now admit that our silent partners have played a significant role. But, there has been very little research on earthworms here. Jill Clapperton had a program underway when at Agriculture and Agri-Food Canada in Lethbridge, Alta., but she is now in Montana. John Reynolds of Kitchener, Ont. documented some species, mostly in urban settings. Most earthworm research has been done in the U.K., Europe, New Zealand, Australia and the U.S.
I think it behooves us to initiate research to document what the worms are doing and how our practices affect them. When anydrous ammonia first came out in the 1970s naysayers said the NH3 would kill the worms. “What worms?” I said at that time. On my Dundurn farm anhydrous ammonia is my main form of nitrogen, applied three years out of four (not on peas). So, obviously anhydrous is not hurting the worms.
We would like to get observations from readers on what you’re seeing as you root around, checking seeding depth in spring. Please clip out the survey on the side. Then mail it in, fax it in, or send us an email to tell us about the worms on your farm. †