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		Earthworm Biology and Production
		Page 3 of 9	Pages: 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9
		Reproduction Earthworms are usually not self-mating although they are hermaphroditic (each individual possesses both male and female reproductive organs). A mutual exchange of sperm occurs between two worms during mating. Mature sperm and egg cells and nutritive fluid are deposited in cocoons produced by the clitellum, a conspicuous, girdle-like structure near the anterior end of the body. The ova (eggs) are fertilized by the sperm cells within the cocoon, which then slips off the worm and is deposited in or on the soil. The eggs hatch after about 3 weeks, each cocoon producing from two to twenty baby worms with an average of four. Earthworms and Soil Productivity Numerous investigators have pointed out the beneficial effects of earthworms on soil properties. Some important effects are the following. Earthworms aid in the degradation of organic residues in the soil with the release of elements such as carbon, nitrogen, sulfur, and other nutrients. The action of the digestive fluids and increased microbial activity in the casts (droppings) tends to solubilize inorganic plant nutrient elements present in inorganic soil minerals. The structural stability of ingested soil is improved through increased microbial activity while the soil is within the worm and after it has been deposited as casts. The extensive burrowing of the earthworm improves soil aeration. Burrowing may also increase water penetration into soils. Under natural conditions the earthworm will feed on surface organic litter and deposit its casts in the plant root zone. Upon further microbial decomposition of the partially digested residues, plant nutrient elements are released. Although earthworms are considered beneficial to soil productivity or plant growth, few valid studies have been made to determine whether their presence will significantly improve plant growth. In one study Hopp and Slater (1949) found that growth of clover was improved by earthworm activity in a poorly aggregated, clay-type soil, but in another study Chadwick and Bradley (1948) were unable to demonstrate increased crop productivity. More studies with a variety of soils and plants are needed to further elucidate this. However, other soil organisms and plant root activity may exert the same or similar beneficial effects on soil properties and positive results may not be expected in all soils. Before considering inoculation (introduction of worms to soil) one should keep in mind that the earthworm is a natural component of the soil population. If the soil is properly managed this natural population will thrive. Soil conditions where inoculation could possibly be of benefit are found in newly prepared farmland or in yards where soils are low in organic matter, dispersed, or very acid and with few indigenous earthworms. In such soils, inoculation with vigorous species and proper management may increase the earthworm population more rapidly than natural processes would. To inoculate, an earthworm species which can adapt to harsh soil environment should be selected, a food source for the worms should be provided, and the soil should be limed if acid. (If a farmer inoculates his soil with earthworms, it will probably be a one-time operation.) Before growing worms for use in commercial agriculture, one should be aware of the above considerations, and should also realize that soil inoculation of commercial farms with earthworms is not a common practice in this country at this time. Spent earthworm manure may be used in a potting mixture, as an organic soil amendment, or as an organic fertilizer. Its nutrient value will depend largely on the nutrient content of the organic products used, and could be considered equivalent to a compost prepared from the same organic residues. However, considerable quantities of nutrients (especially nitrogen) are removed from the residues when worms are harvested. more...

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