5. Conclusions
Enhancement of physico-chemical properties by adding composted
green waste to this contaminated soil included reducing
soil acidity, increasing soil OM, N and P, all of which facilitated
the establishment and growth of perennial ryegrass. Biochar alone
could not produce these effects, due to lowNand P resulting in poor
plant biomass. However, the combination of compost and biochar
had a synergistic effect with a greater efficacy for reducing Pb concentrations
in pore water and uptake to plants. Whilst superior
in this aspect of remediation, the increased biomass of ryegrass
associated with compost application and the enhanced nutrition
it provided negated some of the large reductions in metals, on a
harvestable basis, and may therefore increase the risk of food chain
transfer. The balance between reductions in uptake and increases
in biomass could be subtle but should be managed if transfer is
to be avoided to higher trophic levels, whilst stabilising contaminated
soils. The interaction between biochar and other organic
amendments in soil should now be the focus of further research
if we are to maximise the potential benefits of both.
Acknowledgements