As anyone finds after moving into a newly built home, a yard full of
"sterile" subsoil is a poor substitute for healthy topsoil when it
comes to growing a lawn, shrubs, or a garden. Topsoil brims with worms,
microorganisms, and organic matter. Subsoilmaterial from below the
topsoilusually spells subpar greenery.
Mining companies face a similar problem when reclaiming strip-mined Western
rangeland. But their problem is far more serious: Federal and, often, state
laws require them to replant and establish native vegetation. New research
points to a way to give their efforts a better chance of success.
While rangeland vegetation like sagebrush may look tough, it's delicate. The
plants need all the help they can get from the soil.
"Anything that helps plants tolerate drought is critical in the arid
and semiarid West, especially in disturbed, reclaimed soils," says soil
scientist Gerald E. Schuman, who is with the Agricultural Research Service.
"Disturbing the soildigging, piling, spreading, and compacting
itdestroys soil pores that hold water."
Mining companies, he notes, typically salvage and store topsoil as long as
several years. They put it back only after they finish mining a site.
But Schuman and colleagues at the University of Wyoming at Laramie found
that native vegetation is so needy that mining companies should return topsoil
no more than a few months after it is removed.
Recently, the scientists learned why: Beneficial root-dwelling fungi die off
in topsoil stored too long. The fungi, called mycorrhizae, have hairlike
filaments that funnel water and nutrients to roots, helping plants survive
The scientists learned about the mycorrhizae's role in a greenhouse study.
The soil came from the site of a coal mine in northeastern Wyoming. In fresh
and sterilized batches of this soil, they planted seed of Wyoming big
sagebrusha species that must be replanted by mining companies if it was
present before disturbance.
The seedlings grown in fresh, fungi-rich topsoil survived 3 to 5 days longer
when the soil was allowed to dry. "This could be just the time needed to
tide them over until the next rain," says Schuman, who is in the ARS
Rangeland Resources Research Unit at Cheyenne, Wyoming.
He recommends that topsoil stockpiling be limited to the start of mining
operations and for no more than a few months.
"After that it should, whenever possible, be salvaged and respread
where needed in a single process." By
Don Comis, Agricultural Research
Service Information Staff..
Gerald E. Schuman is in
the USDA-ARS Rangeland
Resources Research Unit, 8408 Hildreth Rd., Cheyenne, WY 82009-8899; phone
(307) 772-2433, fax (307) 637-6124.
"Topsoil Is Alive: Keep It Fresh " was published in the
February 1999 issue of
Agricultural Research magazine.