Tunnel Vision Scientists Toil in the Soil to Better Understand the Role That Earthworms Play in the Underground Environment

Article excerpt

DIANN JORDAN drove the flathead shovel into the ground with her foot and pulled up a chunk of dry, black soil from a recently harvested soybean field.

An earthworm poked its head out from the smooth side of the hole, and Jordan gently pulled it out with her fingertips.

"Here's one," she said, lifting it and showing a visitor how to identify the species among the thousands of kinds known to exist.

Jordan, a scientist at the University of Missouri at Columbia, is studying the role that earthworms play in the complex underground environment of soil, nutrients and water in Midwestern farm fields.

The main site for the study is the Bradford Agronomy Research Center, a farm that's part of the University of Missouri Agricultural Experiment Station about six miles east of Columbia. As Jordan and her colleagues dig there and in a few other spots around the state, they are opening a kind of door on the inner world of life beneath our feet.

It's a world that few of us think about, but scientists have been studying it for a long time. Researchers know much about the animals and plants that inhabit this underground world, but they've only just begun to understand the ebb and flow among the ecological links that connect these organisms and the environment.

The MU scientists hope the study will bring to light new ways to understand soil quality and crop production. They also hope it will improve our understanding of how pesticides and other hazardous chemicals move through the soil - perhaps even into water supplies.

The researchers are studying the number, kinds and distribution of earthworms under various farming practices. They're also examining the ways worms change the physical properties of the soil, including making vast networks of tiny tunnels.

"All that information comes together to make a complete story," Jordan said.

Among discoveries so far, the MU scientists have found that earthworms thrive in soil where they have a good food source from crops aided by fertilizer. Worms also prosper where farmers practice no-till farming, a method that basically leaves the soil untouched by chisel and disk plows.

Charles Darwin, the 19th-century biologist most famous for proposing the concept of evolution, once wrote that earthworms were "lowly" creatures. But, Darwin added, "It may be doubted whether there are many other animals which have played so important a part in the history of the world."

For centuries, farmers, gardeners and others have associated earthworms with healthy soil. But scientists know little about the roles earthworms play in different kinds of farming methods.

Scientists split earthworms into three categories based on where they live: shallow or deep in the soil or in plant litter on the surface. Since the surface dwellers usually cruise through leaves and other dead matter on the forest floor, they're rarely found in farm fields. Shallow and deep dwellers are common in the soil of Midwestern farms.

The deep dwellers, called nightcrawlers, can grow to 8 inches long. A nightcrawler builds a burrow 5 or more feet deep and drags plant residue down to it. The worm covers the top of its long, vertical tunnel to the surface with plant pieces and waste. This cap - called middens - serves as a food reserve and a protective measure.

The shallow-dwelling earthworm plies the top foot of soil in random patterns. This worm usually grows between 3 and 5 inches long. Rather than building a burrow, it eats plant residue and minerals along its trek. Shallow dwellers include the redworm, grayworm and fishworm.

Earthworms are most active in the spring and fall. To escape the heat of summer and cold of winter, shallow dwellers often dig deeper than a foot, curl up in a ball and secrete a protective fluid. Nightcrawlers simply escape to their burrows.

Earthworms improve the health of soil by leaving a wake of nutrient-laden waste. …