Effect of tree harvest intervals on the removal of heavy metals from a contaminated soil in a field experiment

Abstract

Four clones of short rotation coppice (SRCs) were investigated for phytoextraction of soil contaminated by risk elements (REs), especially Cd, Pb and Zn. As a main experimental factor, the influence of rotation length on the removal of REs was assessed. The field experiment with two Salix clones (S1 – (Salix schwerinii × Salix viminalis) × S. viminalis; S2 – S. × smithiana) and two Populus clones (P1 – Populus maximowiczii × Populus nigra; P2 – P. nigra) was established in April 2008 on moderately contaminated soil. For the first time, all clones were harvested in February 2012 (20124y) after 4 years. Subsequently each plot was equally split into halves. The first half of the SRC clones was harvested in February 2014 after 2 years (20142y) and again it was harvested in February 2016 after further 2 years (20162y). The second half was harvested in February 2016 after 4 years (20164y). The results showed that the biomass production for the second 4-year harvest period was significantly higher for all clones but the metal concentration was lower in the mentioned period. 4-year rotation seems to be more advantageous for the phytoextraction than two 2-year rotations. The highest metal removal presented by remediation factors (RFs) per 4 years for Cd (6.39%) and for Zn (2.55%) were found for S2 in the harvest 20164y treatment. Removal of Pb was the highest by P1 clone with very low RF per 4 years (0.04%). Longer rotation is also economically superior.