PRODUCTION POTENTIAL OF STOCKPILED TOPSOIL1

Abstract

Western wheatgrass (Agropyron smithii Rydb.), Indian ricegrass (Oryzopsis hymenoides Roem. and Schult.), and bitter-brush (Purshia tridentata Pursh.) were grown in fresh and stockpiled topsoil in a greenhouse to determine (1) if stockpiled material has lower production or seedling emergence than fresh material, (2) if nonvegetated portions of stockpiles have lower production or seedling emergence than vegetated portions, and (3) if depth of the soil sample within the stockpile influences production or seedling emergence. Fresh soil had substantially higher bitter-brush seedling emergence, production, and mycorrhizal colonization, while stockpiled soil had slightly higher grass production and soil nitrate and phosphorus contents. The vegetated portions of the stockpile had higher bitterbrush seedling emergence, production, and mycorrhizal colonization, while the unvegetated portion had slightly higher grass production and soil P contents. Depth within the stockpile had no consistent effect on seedling emergence, production, mycorrhizal colonization, or soil N and P contents. Across all treatments, bitterbrush production was most closely correlated with mycorrhizal colonization. These results provide evidence that use of stockpiled topsoil on mine sites will have little effect on grass production, but because of the adverse effect on mycorrhizal inoculum, use of stockpiled soil will reduce establishment and production of plant species that have a high dependency on mycorrhizae for nutrient uptake.