Earthworms are the original underground heroes. Their usefulness has been extolled by everybody from Charles Darwin to organic farmers to soil scientists, yet most people spend about the same amount of time thinking about earthworms as earthworms spend thinking about us. Most people, if they think about them at all, consider them only when they’re used to catch fish.
Darwin spent the last year of his life writing about worms, a subject that interested him for more than 40 years. He found them to be deaf (he tested their hearing with whistles and a bassoon) and “timid,” i.e., stupid. But without them, he noted, vegetation in many parts of the world would die.
“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, organized creatures,” he wrote.
We keep rediscovering how important earthworms are, even when we’re looking for something else. That was the case recently when a study by USDA Agriculture Research Service (ARS) scientists compared nutrient and sediment loss from no-till, conventional tillage and reduced input practices on cropland in different watersheds. The findings were published online this month in the “Soil Science Society of America Journal.”
The study found that no-till practices, in which the ground is not plowed or broken up, can reduce soil erosion but might lead to increased runoff of dissolved phosphorous (P) from the soil, especially when herbicides are used to control weeds that would otherwise be controlled by tilling. But in comparing the dissolved P from no-till and conventional tillage watersheds, researchers found little difference.
By trying to figure out why, the researchers rediscovered the earthworm. Lead investigator Martin Shipitalo said it’s was a matter of simple biology. “The biology of the soil changes with long-term no-till,” Shipitalo said. “By leaving residue cover, you increase organic matter, and you increase earthworm populations.”
Other studies have reached similar conclusions. A study by soil agronomist Eileen J. Kladirko of Purdue University in the early 1990s compared earthworm populations and benefits in no-till fields compared to conventionally tilled fields.
“The mixing of organic materials and nutrients in the soil by earthworms may be an important benefit of earthworms in reduced tillage systems, especially no-till,” she wrote. “The earthworms may, in effect, partially replace the work of tillage implements in mixing materials and making them available for subsequent crops…It seems appropriate, therefore, to try to determine how we can manage soils to encourage the organisms and their activity.”
The organic residue on top of the ground impacts soil temperatures and moisture, which affects the worms as they burrow deeper and deeper into the ground — seven feet or more — creating little water channels and leaving behind nutrient-rich castings as they go. In agriculture, earthworms are almost always beneficial, but they are not absolutely necessary.
“Some soils can be very productive without the presence of earthworms,” Kladirko wrote. “The worms have sometimes been shown to improve crop growth and yield directly, but more often their activity affects crop growth indirectly through their effects on soil tilth and drainage.”
A 1982 book by Mary Applehoff titled “Worms Can Eat My Garbage” introduced us to vericomposting, a system that includes raising worms like livestock by corralling them in a bin and feeding them certain organic material, especially kitchen scraps but excluding meat, citrus and a few other things earthworms don’t care for. The worms eat the scraps, excrete the castings, and at the same time release valuable minerals into the soil.
Of course, most worms raised and sold commercially enter the food chain on the end of a hook as fish bait. The vast billions left over will continue working underground, perhaps helping to bring forth nutrient-rich vegetables to serve with the fish we caught with the worm. Not a bad contribution for an underground (or underwater) worker.