Evaluation of Flue Gas Desulphurization (FGD) Ash and Fe-Rich Biosolids as Soil Amendments to Remediate Zn Phytotoxicity.

Phytotoxicity of excessive soil Zn can be remediated by stabilization of bioavailable Zn in the soil with either Flue Gas Desulphurization (FGD) ash or Fe-rich biosolids (Fe-biosolids). These residuals can reduce soil bioavailable Zn by surface precipitation, adsorption to mineral surfaces, and/or ion exchange. Using an experimental field in which Zn toxicity was observed for over 20 yrs, we evaluated the suitability of FGD and Fe-biosolids as amendments to remediate Zn phytotoxicity. A Metea loamy sand soil (loamy, mixed, mesic Typic Hapludalfs) treated between 1977 and 1986 with sewage sludge at 0, 1.43, 2.67, and 11.3 Mg Zn ha^-1 (four replicates each) showed Zn phytotoxicity at the highest Zn loading between 1985 and 2006. In 2007, we initiated a study to evaluate FGD and Fe-biosolids as amendments to stabilize and reduce Zn phytoavailability and remediate the phytotoxicity. Three portions (6.1 m x 6.1 m each) of each replicate plot of the three Zn loadings plus controls (no Zn loading) were randomly treated with either 25 Mg FGD ha^-1 (split applied as 16 and 9.0 Mg ha^-1 in 2007 and 2008, respectively) or 112 Mg Fe-biosolids ha^-1 (single application in 2008) or left untreated. Soybean (Glycine max L.) was grown to maturity in 2007 and 2008. The FGD and Fe-biosolids each reduced plant Zn uptake and improved the yield of soybean grown in 2008 on Zn phytotoxic plots. Yields of soybean harvested from Zn phytotoxic plots treated with FGD was not different from yields observed in control plots at P = 0.05. While soybean yields were also increased by the Fe-biosolids, yields were still lower than those observed in control plots or FGD-treated plots. The FGD and Fe-biosolids amendments have the potential to reduce Zn phytoavailability and phytotoxicity, but at the rates applied in this study, FGD is more effective at remediating Zn phytotoxicity than Fe-biosolids.