June 2, 2010

Charles Darwin and earthworms

Charles Darwin wrote, "It may be doubted that there are many other animals which have played so important a part in the history of the world as these lowly organized creatures."

Many of us may debate the "lowly" designation given to the earthworm because it is very difficult to argue their profound impact on natural and agricultural soil fertility. Earthworms range in size from an inch to 12 feet or more in length. There are more than 2,500 earthworm species and most of these species eat their way through soil, extracting organic material in the process and excreting the remainder on te surface as pellets, or often called castings. One could say that they are natures soil mixers, mixing the upper and lower levels of soil. This process makes minerals more available to plants. The castings also serve as plant fertilizer and increase the soil's water-holding capability. Earthworms create tunnels that serve as pathways for water, plant roots, and gas exchange. They feed on leaf litter and in the process assist in seed dispersal, decomposition, and the prevention of serious fungal diseases that affect agricultural crops.

Darwin estimated that the burrowing of 50,000 earthworms turns over 18 tons of soil annually. Over 2 million earthworms may populate a single acre of farmland.

Source: Sierra Club, Frank Indiviglio

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