Dishing the dirt has a long history in Washington, but the Smithsonian Institution is taking it to new depths. The National Museum of Natural History opens a new exhibit on Saturday _ "Dig It" _ exploring the mysterious and complex world of soil.

"We want people to walk away understanding that soils are living, living breathing bodies," said exhibit curator Patrick Megonigal, a soil ecologist at the Smithsonian Environmental Research Center in Edgewater, Maryland.

"One of the most important messages for me is that people get beyond thinking of soil as something in their garden, but think of it as the foundation of all the Earth's ecosystems," as important as air and water, he said.

There's no mudslinging in this exhibit; it stresses that most life on the planet depends on soil one way or another, yet it's a subject with many secrets yet to be spaded up.

While the biggest environmental problem right now is climate change, "just over the horizon is learning how to make agriculture sustainable," said David Montgomery, a soil geomorphologist at the University of Washington.

"We face some very basic choices over next 50 years and one of those is to reinvest in our soils," Montgomery said in a telephone interview.

In many areas, he explained, soil is being eroded faster than it is being replaced. "We usually take it for granted, it's just dirt, after all."

But, he added: "Soil is one of the basic bits of the foundation of life. Soils are created, destroyed and transformed. They can be used up just like any other resource," Montgomery said.

The chemical and physical properties of soil help clean and purify rainwater that passes through, added Diana Wall, a soil ecologist at Colorado State University.

American researchers recognize 12 orders of soil, Megonigal explained, ranging from frozen tundra to deserts to volcanic. Look for more detail and the orders can be divided into 70,000 soil series.

"The variability is just numbing," he said.

Soil can even bring on nostalgia _ Agriculture Secretary Ed Schafer spoke longingly at an exhibit preview of missing the smell of the rich, deep soil of his native North Dakota.

Air and water get more attention, said Rep. Jim Costa, D-Calif., but the necessities of life are like a recipe, you need all the ingredients, air, water and soil.

After families come through this exhibit, added Rep. Tom Latham, R-Iowa, "the kids will look at mud a whole lot different."

Visitors can, at least figuratively, get down and dirty at such displays as:

_ "At Home in the World of Soils," a gallery where people can learn about the connections between soil and culture. It includes a scale model of a suburban house lot that highlights soils in and around our homes.

_ A video features soils as the "secret ingredients" in thousands of everyday items including medicine, food, fiber, paint, cosmetics, and pottery.

_ An "Underneath it All" gallery includes a topographic model to illustrate the role of soils in residential, urban and agricultural areas.

_ Touchable soil samples provide close-up looks of two different urban soils found in Washington, D.C. Continued...