METAL CONTENT OF PLANTS AND SOILS IN A TREE NURSERY TREATED WITH COMPOSTED SLUDGE

Digested sewage sludge compost from Washington, D.C., was applied to a Downer sand at rates of 0, 56, 112, 224, and 448 dry metric tons/ha. A fertilized control treatment was also utilized. Pearl millet (Pennisetum americanum [L.] K. Schum.) was grown as a summer cover crop prior to fall tree seeding. Leaf samples of red oak (Quercus ruba L.) and black walnut (Juglans nigra L.) seedlings were taken the summer of the first growing season. The total metal contents (μg/g) of the compost were 2,154 Zn, 517 Cu, 13.9 Cd, and 69 Ni. The treated soils were monitored for DTPA extractable Zn, Cu, Cd, and Ni throughout the 2.4 years of the experiment. No visual, foliar effects were noted on the growth of pearl millet or tree seedlings from the increasing rates of compost, however, pearl millet tissue Cd levels were significantly increased with increasing levels of compost from about 0.40 to about 1.62 μg/g. Metal contents of the tree seedlings were low and within normal levels recorded in the literature. Extractable soil Zn, Cd, and Cu decreased with time, however, soil Ni extractability tended to increase with time. Compost additions resulted in an increased soil pH which was maintained throughout the experiment. Poor correlations (r2 ranged from 0.002 to 0.543) were obtained between DTPA extractable metals and metal concentrations of pearl millet, red oak, or black walnut.