Short Rotation Coppice Culture of Willows and Poplars as Energy Crops on Metal Contaminated Agricultural Soils

Abstract

Phytoremediation, more precisely phytoextraction, has been placed forward as an environmental friendly remediation technique, that can gradually reduce increased soil metal concentrations, in particular the bioavailable fractions. The aim of this study was to investigate the possibilities of growing willows and poplars under short rotation coppice (SRC) on an acid, poor, sandy metal contaminated soil, to combine in this way soil remediation by phytoextraction on one hand, and production of biomass for energy purposes on the other. Above ground biomass productivities were low for poplars to moderate for willows, which was not surprising, taking into account the soil conditions that are not very favorable for growth of these trees. Calculated phytoextraction efficiency was much longer for poplars than these for willows. We calculated that for phytoextraction in this particular case it would take at least 36 years to reach the legal threshold values for cadmium, but in combination with production of feedstock for bioenergy processes, this type of land use can offer an alternative income for local farmers. Based on the data of the first growing cycle, for this particular case, SRC of willows should be recommended.

KEY WORDS:

• soil contamination
• phytoextraction
• soil remediation
• bioenergy
• cadmium

ACKNOWLEDGMENTS

The experimental field was a pilot project set up in 2004 in a study by order of OVAM, under responsibility of Hasselt University (Centre for Environmental Sciences, Environmental Biology Group). Research funded by the Fund for Scientific Research Flanders (FWO-Vlaanderen) for JB and by the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen) for NW and JD. Funding was also obtained from the Methusalem project 08M03VGRJ. The Salix viminalis ‘unknown’ was a gift from Prof. Maria Greger (Department of Botany, Stockholm University).

Notes

^a‘Normal range’ values in sandy soils in Flanders according to De Temmerman et al. (2003).

^bClean up values for remediation of a ‘standard’ agricultural soil (2% organic matter and 2% clay) according to the Flemish legislation on soil remediation (VLAREBO 2009).

*V = Salix viminalis, F = Salix fragilis, D = Populus deltoides; N = Populus nigra; Tr = Populus trichocarpa.