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June 01, 2009

Earthworms

Devin Foote is a 24-year-old beginning farmer at Common Ground Farm in Beacon, New York. Throughout the growing season, Devin will be chronicling his experiences as a young farmer growing for a local food system.

May 28, 2009

The overcast, coastal-like mists have brought my attention to what is beneath all of the weeds that we are trying to stay on top of. And whenever I make a new pass through the field with the disc, I turn around to see swooping blue birds, yellow finches, and baby kill deer scurrying by to harvest the day's fresh offerings. My hand claps and whistles are never frequent enough to keep them away from our friend in the soil, Lumbricus terrestris.

The earthworm is a special sort of worm. Almost alone among its brethren, the earthworm does not inspire horror. In fact, the earthworm is almost alone among all invertebrates in the tenderness it inspires. Knowing that a worm in the sun is as good as dead—since its skin has no defense against desiccation—children often place them gently in the shadow of a log or cover them with a light handful of soil. We all remember our interaction as children with earthworms—be it a friend's earthworm box in their room or digging them up before going fishing with Dad. Without question, gardeners—above all—venerate the worm.

In his book Dirt: The Estatic Skin Under the Earth, William Bryant Logan points out much of what we already know: when worms are happy, there are lots of them. It is said that in a Danish forest soil, researchers have found a density of one million to one-and-a-half million worms per acre—more than two tons of worms! A rich grassland may bring up more than 500 worms out of a square-meter hole. This is not so remarkable when you recognize that eight relatively healthy worms will produce 1,500 offspring in half a year’s time.

The common earthworm is not native to the United States, having been brought over by colonists in the mid-nineteenth century. When it first appeared, it was not numerous. But as fields were cleared, its numbers increased to such a degree that the water of springs and wells became polluted by the number of dead worms. As often witnessed in nature, the corresponding introduction and increase of robins and other vermivores corrected the imbalance.

Regardless, the presence of earthworms is by and large a very good thing for the soil. Unlike a given fertilizer, it acts simultaneously on several different soil variables.

More than any other creature, the worm defines topsoil. Worms are basically blind; therefore, they see literally by eating. A worm is a long intestine. Soil, rich in dead organic matter, leaves, and especially manure, goes in one end and comes out the other—concentrated, enriched and well mixed—in the form of “castings.” Castings are so rich a source that at the farm I worked at last year, in preparation for making our potting mix, we would take a shovel and bucket into the woods, peel back a few leaves and collect two gallons per batch. It is said that a well-manured soil is almost always rich in worms. Up to ten tons of worm castings per acre per year enrich a soil under favorable conditions. The worm also senses and creates the topsoil in a very basic way: by going where the organic matter is, mixing it, and excreting it behind or above itself. Worms also bore down to the water table, but not into it. At the dry surface, too, they stop.

Some earthworms leave their castings on the surface, others in the body of the soil. These castings concentrate nutrients. Scientists estimate that worm castings contain five times more nitrogen, seven times more available phosphorus, 11 times more potash and 40 percent more humus than is usually found in the top six inches of soil. In addition, the castings mix the soil ingredients, facilitating further breakdown by microbes.

The earthworm's blindness does not hinder its motion; worms are pathfinders. A single acre of cultivated soil has been found to have more than six million worm channels whose presence significantly increases the soil’s ability to hold and percolate water. A clayey orchard soil had more than two million large channels—some the size of a little finger—in an acre, the equivalent of a two-inch drainage pipe! Others have found that down to a depth of four inches, up to 50 percent of the soil’s air capacity consists of the tunnels and cavities dug by worms.

Earthworms are the watchers of the soil. If you build soil, worms will come.

Now that our cover crops have been dried and turned under, the organic matter of which they are composed is the perfect food source for microorganisms and earthworms. As ecologically senstitive farming goes, large amounts of earthworms and microorganisms are often present in abundant numbers. We hope that our well-managed soil will pay off as we harvest for our first market this weekend and start our first distribution next Tuesday. Here's to the earthworm!   

Devin Foote

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