Plant Availability of Phosphorus and Heavy Metals in Soils Amended with Chemically Treated Sewage Sludge

Abstract

AbstractThe objective of this study was to evaluate the effect of sludge chemical treatment (Al3+, Fe3+, and Ca2+) on P and heavy metal availability in sludge‐amended soils.Municipal sewage sludge treated with the chemicals Al2(SO4)3, FeCl3, or Ca(OH)2, along with untreated sludge and monocalciumphosphate (MCP; Ca(H2PO4)2·H2O) fertilizer, were applied to acid, neutral, and alkaline soils at rates equivalent to 83, 125, 250, and 500 kg P ha−. Swiss chard (Beta vulgaris) was grown in these soils to maturity with leaf samples taken 38, 54, and 70 d after planting. Swiss chard yields were determined and plant tissue analyzed for P, Zn, Fe, Mn, Cd, Ni, and Pb. Soil samples were analyzed for HCO3‐extractable P and pH.Zinc and Manganese concentrations in plant tissue were significantly higher (P <0.05) for the Al‐treated sludge at an application rate of 500 kg P ha−1 in the acid soil. Plant Cd levels were significantly higher (P <0.01) for the Al‐treated sludge at application rates of 250 and 500 kg P ha−1 in the acid soil. The increased plant levels of Zn, Mn, and Cd appear to be the result of a lower soil pH produced upon the addition of Al‐treated sludge. No significant differences in Fe, Ni, and Pb concentrations were observed in the plant tissue for any of the treatments or application rates.Bicarbonate‐extractable P was greater where MCP was applied than where any sludge was applied in the acid and alkaline soils; however, no discernible trends in P uptake by the chard were observed for any of the fertilizer treatments or application rates. Phosphorus was equally available from the sludges and MCP in the acid and alkaline soils.