Switchgrass cultivation potential in soils contaminated with heavy metals

Due to contamination and marginalization of the soils, several environmental problems such as desertification, contamination of water resources, and contamination of food crops, and occur, which can lead to serious health problems for humans directly or indirectly. To tackle these problems, a wide range of techniques can be applied to decontaminate the soils using physical, chemical, and biological methods. The utilization of crops for the decontamination of soils (phytoremediation), and specifically the use of energy crops, is an promising alternative. Along with the decontamination action, the biomass produced may provide an additional income, when used for bioenergy or biomaterials, and the process contributes to the bioeconomy by reducing the dependence on fossil fuels. Therefore, this work aimed to study the effects of different heavy metals (Zn, Cr, Pb, Cd, Ni, Cu) on switchgrass (Panicum virgatum L.) growth, productivity, and biomass quality during a two years experiment. The soils were artificially contaminated and the concentrations chosen were twice the limits established by the Decree-Law 276 of 2009 (Portuguese regulation that determines the regime for the use of sewage sludge in agricultural soils) - Zn: 900 mg/kg; Cr: 600 mg/kg; Pb: 900 mg/kg; Cd: 8 mg/kg; Ni: 220 mg/kg and Cu: 400 mg/kg. Results indicate that for all the contaminants, productivity and the height in the second year were higher than in the first year. Also, Cr contamination has inhibited the germination of switchgrass seeds in both years. Results indicate that for the first year due to the low development of the root system, the productivity decreased for Cd and the decrease in productivity was critical for Ni and Cu contamination, once the biomass production was almost null, but not for Zn in Pb contamination. For the second year, with the root system better established, the influence of the contaminants in biomass productivity was lower than in the first year. For Zn, Pb, Cu, Cd and Ni contamination, the productivity was higher than in the first year, although lower than yields of the control pots, while for Cr contamination, the productivity remained null. Yet, contamination affected the quality of the biomass. Ash content increased and the heating value decreased, which may limit the technological exploitation of the biomass.