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This week’s Book of the Week feature is Secrets of Fertile Soils, by Erhard Hennig.

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From Chapter 7: Earthworms and the Fertility of Soil

Earthworms exist everywhere in the world. They even populate isolated groups of islands. The presence of earthworms in uncultivated soils can be explained by the fact that birds, which take in earthworm egg capsules along with the worms on which they feed, excrete them intact.

In recent years, many researchers from all over the world have drawn our attention to the earthworm and have reported about this creature in scientific publications. The surprising discoveries made about these creatures are of interest not only to farmers and gardeners but also to biologists, geologists, and environmentalists. However, farmers and gardeners wait in vain for this scientific research to be put into practice. The chemical methods of fertilization and pest control that modern agriculture relies upon (mineral salts, pesticides) have an annihilating effect on earthworms. There are already “cultivated soils” in which earthworms have been completely wiped out.

The Earthworm Species and their Position in the System

All (German) earthworm species belong to the lumbricides family, which is a subspecies of the annelids. Zoologists distinguish between three different classes of annelids:

  • primary annelids
  • bristle worms
  • clitellata

Annelids and bristle worms only exist in the sea. Clitellata, whose name is derived from the presence of a collar, or clitellum, can live on land or in water. Our earthworms are true terrestrial animals. They ought to be regarded as superior to the other worms. The most common earthworm species in Germany are:

  • Eisenia foetida, which is otherwise known as the manure compost worm. It lives predominantly in dung and compost heaps.
  • Allolobophora longa and subspecies.
  • Lumbricus terrestris and subspecies.

About thirty-five different species of earthworm can be found in Germany. The length of native earthworms varies from 1 to 12 inches. In the tropics, giant worms thicker than a human thumb and from 2 to 6 feet in length can be found.

The Anatomy of the Earthworm

The earthworm feeds mainly on soil containing microorganisms (bacteria, fungi) and sometimes decomposing organic matter. However, it cannot bite because it has no teeth; earthworms are only able to swallow. Because they have no eyes or ears, earthworms have a very keen sense of touch. The earthworm’s body is divided into several rings, or segments, that are joined to one another. These rings are covered with bristles and are used to propel the worm forward. The mouth opening can be seen in the first ring, and in the last ring is the end of the intestines (i.e.: the anus). The mouth opening leads to the pharynx, which adjoins the esophagus. Its final segment contains glands designed to release lime. Thus the humic acids taken in by the worm along with its nutrition (soil) are neutralized. Lime assists with the preservation of the base-acid balance.

The esophagus leads to the enlarged crop. A special intestinal section, known as the muscle stomach, joins to this part. Compared to all the other sections of the digestive channel, the intestine musculature is built up very strongly in this section. The digestive part of the intestines, which reprocess the vegetable and animal matter consumed along with the earth, is below the muscle stomach. Indigestible earth is excreted from the other end of the worm in the form of the easily recognizable worm casts.

France used the term “coprogene humus deposit” (meaning humus produced from excrement) to describe the feces. Earthworm humus is the best humus in existence.

A heart-like organ circulates the worm’s blood, which can be easily observed in young earthworms.

The worm’s nervous system consists of a brain and one pair of peripheral nerves. Organs of touch are spread all over the body. Though the creatures do not possess eyes, they can react to luminous stimuli. Earthworms are always hermaphroditic, which means that any given worm possesses both male sexual organs as well as female eggs. Reproduction happens in a complicated way through the mutual transfer of sperm cells, in which both animals act as males and females at the same time.

In most species, mating occurs in the soil. Lumbricus terrestris is the only species that can also copulate on the surface.

During the development of earthworm embryos occurs a ring-like thickening, known as a cocoon.

The cocoons containing the eggs are put in the upper soil zone, but only where there is enough moisture available. Earthworm eggs are very often found in compost piles. The tiny eggs are 1-2 millimeters long, brownish or yellow-green in color, and visible to the naked eye. Breeding farms produce six hundred worms yearly. Baby worms usually slip out of the cocoon after three or four weeks.

The Life of the Earthworm

Earthworms are creatures that eat nonstop, but their demands are few:

  • They love humidity.
  • Their life takes place in the dark, and they are killed if they are exposed to the light without protection.
  • They are happiest at temperatures of between 64-86 degrees Fahrenheit.
  • A good supply of organic waste is essential to them.

Earthworms do not live off the mineral elements in the soil, as was previously assumed, but rather off the organic substances in the soil. Waste from rotting onions, citrus fruits, leeks, fruit remains, and coffee grounds are special favorites of the worm.

Earthworms do not, however, feed solely on the decomposing organic substances available in the earth; they can also be viewed as omnivores. Apart from organic substances, worms also take in countless living vegetable and animal organisms along with the soil, such as bacteria, algae, fungi mycelium, and fungi spores.

In order to stay alive and maintain its ability to perform, the earthworm needs to consume its own body weight in nutrition every twenty-four hours.

Let us assume that on one hectare (1 hectare = 2.5 acres) of farm land there are 1 million earthworms (Lumbricus terrestris) with a total weight of 2 tons. These animals must take in around 2 tons of nutrition daily in order to stay alive and to reproduce. A considerable achievement! While earthworms must consume a biomass of 2 tons beneath each hectare of earth, this same space above ground can only feed one or two cows with a weight of 1,700-2,200 pounds. That means that in a fertile soil, almost twice as many organisms (by weight) can be fed underground than on the surface.

Learn more about Secrets of Fertile Soils here. 

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About the Author:

Erhard Hennig was an agronomist who devoted himself to agriculture from an early age. He worked extensively as a farmer, agricultural consultant, journalist, author, and lecturer and work and taught at Humboldt University in Berlin. Hennig died in 1998. 

Titles of Similar Interest:

The Farm as Ecosystem, by Jerry Brunetti

Healthy Soil, Sick Soil, by Margareth Sekera

Foundations of Natural Farming, by Harold Willis

Compost Revolution, by Helmut Schimmel (Translated by Paul Lehmann)