The long-term potential for sewage sludge amendments to alter forage trace metal concentrations was determined on bromegrass, which received no sludge application for 20 yr following annual application during 1973-1980 on a no-till randomized-plot experimental site. In addition, soils were analyzed for trace metals, both total and extractable (using hot 0.01 M CaCl2), by axial-view inductively coupled plasma spectrometry. For Cu, Ni, Zn and Cd, extractability from the soil (by CaCl2) as well as plant tissue concentrations were relatively low considering the high loadings of these particular metals, a fact attributable to the near-neutral pH and high organic matter content of these calcareous soils. However, total and extractable soil Mo remained elevated in the sewage-sludge-amended plots above the levels measured in the fertilized control plots some 20 yr after the last sewage sludge application. Mo bioaccumulated in the bromegrass more than the other trace metals investigated at this site. The Cu:Mo ratio in the forage, a measure of potential to induce Cu deficiency in grazing ruminants, was substantially depressed by most of the sewage sludge treatments. Comparison of the 2000 and 1980 bromegrass analyses suggests an increase in the long-term plant availability of Mo in soils amended with high-Fe and high-Al sludges. Conversely, there was a long-term decrease in Mo availability on the high-Ca sludge treatment, consistent with evidence that much of the Mo has been lost from the topsoil since sludge application. For Cu, Ni and Zn, plant availability appears to have decreased between 1980 and 2000, attributable in part to a calculated loss of substantial fractions of these metals from the topsoil. Bromegrass concentrations of Cu, Ni, Zn, Cd and Mo were strongly correlated to CaCl2-extractable and total metals in the soils, indicating the utility of 0.01 M CaCl2 in predicting plant availability. The chemical differences in the three sludge types applied at the site (high-Ca, high-Al, high-Fe) had little long-term impact on the extractability and phytoavailability of most trace metals remaining in the topsoil. Key words: Biosolids, molybdenum, copper, forage, cadmium, heavy metals
Long-term Impact of Sewage Sludge Application on Rhizobium leguminosarum
biovar trifolii
: An Evaluation Using Meta-Analysis