EFFECT OF MUNICIPAL SEWAGE-SLUDGE APPLICATION ON GROWTH OF 2 RECLAMATION SHRUB SPECIES IN COPPER MINE SPOILS

One-year old transplants of fourwing saltbush [Atriplex canescens (Pursh) Nutt.] and mountain big sagebrush [Artemisia tridentata ssp. vaseyana (Rybd.) Beetle] were grown for 9 mo in large greenhouse pots containing copper mine spoil material amended with one of three rates of municipal sewage sludge. Sludge was thoroughly mixed with the soils in some pots and concentrated around the root plug in others. Additionally, some pots were seeded with western wheatgrass (Agropyron smithii Rydb.) to determine whether the presence of grasses would affect shrub response to sludge addition in low pH copper mine spoils. Growth of fourwing saltbush was enhanced from 38- to over 300-fold by the addition of sewage sludge. Growth of big sagebrush was increased over six-fold. This was likely the result of increased N, P, and K availability, although improved biological and physical properties of the spoil-sludge mix may also have been factors. The addition of western wheatgrass to pots containing fourwing saltbush caused a decrease in shrub growth, undoubtedly due to competition for nutrients and other plant growth factors. At the conclusion of the study, shrub leaves contained high levels of Cd and Pb, reflecting the high Cd and Pb content of the growth medium. Zinc, Cu, Mn, and Fe levels were also largely higher than are typical for plant tissue. Shrubs grown in pots in which sludge additions were concentrated around the root plug accumulated more heavy metal than did mixed treatments. Grass tissue did not accumulate excessively high quantities of heavy metals, with the exception of Cu.