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As the harmful effects of agricultural chemicals become more evident, farmers are turning to alternative agricultural methods to replenish lost nutrients in the soil. One of the most promising techniques is the addition of earthworms.

Farmers have long regarded worm content as a measure of healthy soil, but researchers at the National Soil Tilth Laboratory at Iowa State University have been turning this time-honored tale into a quantifiable fact.

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Ed Berry has discovered that, under research conditions, the presence of earthworms ``correlates with a 4 to 10 percent increase in filtration rates of water into soil, a 30 percent increase in decomposition of leftover [crop] residue, and improved yields.''

A brochure that the lab distributes among farmers explains that earthworms swallow and digest organic matter as they tunnel, recycling plant and animal wastes into nutrients.

Each day, a worm ingests its own weight in soil. Worm castings are rich in minerals and promote the growth of microorganisms.

Worms also foster healthy crops through their tunneling: Tunnels let more oxygen into the soil, provide more room for plant roots, and allow more water to reach these roots.

All this is good news for farmers, because worms are a cheap alternative to spraying fields with more pesticides, herbicides, and chemical fertilizers. According to Dr. Berry, all the worms need is ``a food source, and a roof over their heads.''

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