The soil beneath our feet is teeming with organisms, each with an incredibly important role in the pedosphere. Among the organisms is a group commonly referred to as earthworms (from the phylum Annelida).
(video on earthworm scouting is at the end of this post)
Though a few species are said to remain from the last ice age, most of the earthworms found in Canada are actually invaders (likely introduced from Europe when ships carried soil ballast or pioneers brought plants bearing soil over). For the most part, these invaders do a pretty bang-up job of improving the soil in non-forested areas, and are revered in agricultural communities as indicators of soil health.
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Earthworms contribute to arable soils by:
Accelerating nutrient cycling – Casts excreted by earthworms are rich in nitrogen, phosphates and potassium. Of course, the below amendments also accelerate nutrient cycling by aerating and mixing the soil, and improving moisture retention.
- Aerating the soil – Besides creating tunnels, the mere action of earthworms moving through the soil forces air through the soil.
- Improving soil structure – The tunnels and burrows increase soil porosity, thereby improving water percolation, and decreasing erosion.
- Adding to the diversity of organisms in the soil (and providing food for their predators in the food web).
Charles Darwin, from EarthwormsThe plough is one of the most ancient and most valuable of mans inventions; but long before he existed the land was in fact regularly ploughed, and still continues to be thus ploughed by earth-worms. It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures.”
Assessing Crop Land
If your crop land has a good earthworm population, you should be able to see 4-5 middens between your feet, if they’re shoulder width apart, says Anne Verhallen, soil management specialist with Ontario Ministry of Agriculture, Food and Rural Affairs. Middens are a mixture of plant residues and worm droppings that often cover the mouths of earthworm burrows. Their function isn’t completely understood, but most scientists agree they provide food and shelter for the earthworms, while possibly also mitigating the risk of predation. …continues below video
Improving Earthworm Numbers
If you’re not terribly impressed with the earthworm populations on your farm, there are a few things you can do to increase their numbers, including:
- Adding manures and/or compost
- Diversifying your crop rotation to include both perennials and annuals
- Decrease tillage
- Leaving at least some of the residue from the previous crop
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