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SONOMA, Calif. – Under rows of old chicken sheds, Jack Chambers has built an empire of huge metal boxes filled with cattle manure and millions of wriggling red worms.

“My buddies all had planes and boats,” said Mr. Chambers, 60, a former airline pilot. “I have a worm farm.”

Mr. Chambers’s two decades of investment in what he calls an “underground movement” may be paying off. New research suggests that the product whose manufacture he helped pioneer, a worm-created soil additive called vermicompost, offers an array of benefits for plants – helping them grow with more vigor, and making them more resistant to disease and insects, than those grown with other types of composts and fertilizers.

The earthworm’s digestive process, it turns out, “is a really nice incubator for microorganisms,” said Norman Q. Arancon, an assistant professor of horticulture at the University of Hawaii at Hilo.

And these microbes, which multiply rapidly when they are excreted, alter the ecosystem of the soil. Some make nitrogen more available to plant roots, accounting for the increased growth. The high diversity and numbers of microbes outperform those in the soil that cause disease.

By contrast, Dr. Arancon said, soil that has been heavily exposed to synthetic fertilizers, pesticides and herbicides lacks microbial richness and diversity, qualities that can be restored naturally by adding the microbes from worms.