Availability of Cu, Zn and Pb from a Contaminated Soil Cropped with Switchgrass and Reed Canary Grass.

More information about the availability of metals is needed for beneficial use of contaminated soil for the production of perennial bioenergy crops. A project was initiated to study the availability of metals from a contaminated soil cropped with Switchgrass (SG) (Panicum virgatum L.) and reed canary grass (RCG) (Phalaris arundinacea L.). These crops are increasingly studied to determine their potential as bioenergy crops. Soils were sampled (0-20 cm) on a contaminated site adjacent to a former incinerator (Lévis, QC, Canada). Soil properties were highly variable across the 0.7-ha field. The soil texture varied from clay to coarse loamy sand. The clay content varied from 63 to 444 g kg-1 (mean = 153 g kg-1), the pH from 5.5 to 8.3 (mean = 7.4), and the soil total carbon from 3.2 to 70 g kg-1 (mean = 23.7 g kg-1). A randomized complete block design with four replicates for a total of 8 plots was established in the spring of 2015. Soil samples were taken annually in the spring to assess the availability of metals from the contaminated soil. We evaluated the availability of metals using three different methods: plant available (DTPA), soluble and exchangeable (Mehlich-3), and total forms. We analyzed soil Cu, Pb and Zn contents in 2015 and 2016. No significant changes in the soil DTPA contents were observed from 2015 to 2016. Average over years, the mean concentrations of DTPA extractable Cu, Pb and Zn were 16, 63 and 40 mg kg-1, respectively. No significant changes in the soil DTPA contents were observed between crops except in the soil DTPA extractable Pb which was higher in the SG compared to the RCG plots. A significant decrease in the Mehlich-3 and in the total contents of Cu, Pb and Zn was observed in 2016 compared to 2015. Those results may suggest that the soil cultivation favored the availability of metals and were either absorbed by the plants or lost via surface water runoff. Analysis of the Cu, Pb and Zn contents in plants and in the soil solution (lysimeters) will be performed to determine the movement of these metals in the sol-plant-water continuum and determine the potential of using this biomass as feedstock for bioenergy production.