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Topsoil: Keeping It FreshBy Don Comis
February 26, 1999
Stockpiled soil--and its wealth of plant-helping fungi--will get stale if "left on the shelf" too long, according to an Agricultural Research Service scientist in Wyoming.
The finding could boost the odds for reclaiming strip mines on western rangeland. It may also help explain why lawns, shrubs and gardens planted in yards of new homes may not thrive if they're planted in near-sterile subsoil instead of topsoil brimming with earthworms, helpful microorganisms and organic matter.
Federal and often state laws require mine companies to reestablish native vegetation. But they typically salvage and store the original topsoil several years before putting it back. Plus, digging, piling, spreading and compacting soil destroys its water-holding pores. This lowers the odds that sagebrush and other range vegetation can struggle through a drought.
Native vegetation is so needy that topsoil removed from a site should be returned within a few months or even respread on another site right away, if possible, according to soil scientist Gerald E. Schuman at ARS' Rangeland Resources Research Unit in Cheyenne, Wyo.
In a greenhouse study, Schuman and University of Wyoming colleague Peter Stahl found that mycorrhizae--beneficial root-dwelling fungi--will die in topsoil stored too long. But the living fungi's hairlike filaments can funnel water and nutrients to roots.
In fresh and sterile batches of soil from a northeastern Wyoming coal mine site, the scientists planted seeds of Wyoming big sagebrush. In fresh, fungi-rich topsoil, seedlings survived 3 to 5 days longer after the soil dried out. Those few days might be a crucial bridge allowing plants to survive until the next rain.
ARS is the U.S. Department of Agriculture's chief scientific agency. A story about the research appears in the February issue of the agency's Agricultural Research magazine and on the World Wide Web at: