The green waste compost amendment reduced the pore water
and ryegrass (Lolium perenne L. var. Cadix) shoot
Pb concentrations, while biochar application reduced
Cu content in pore water and ryegrass shoot, indicating
the metal specific suitability of these amendments for
treating a heavily Cu- and Pb-contaminated soil from a
former copper mine (Karami et al., 2011). Reverchon et
al. (2015) reported that jarrah biochar soil amendment
(37 and 74 t ha−1) increased soil C/N ratio, photosynthetic
N use efficiency, and biological N fixation rates
of a native legume (Acacia tetragonophylla) grown in
a mixture of topsoil and mine rejects, indicating positive
effects on soil properties and plant nutritional status.
However, Kelly et al. (2014) could not find any
changes in microbial population or activity in mining
waste upon biochar application. Therefore, the characteristics
of the substrate to be treated are crucial for
the biochar selection. Biochar has turned a wasteland
enriched with As, Cd, Pb, and Zn on a steep mountainside
into a haven for natural grasses and wildflowers
that have stabilized the slope and almost diminished
the risk of heavy metal leaching into the city’s main
water supply around Hope Mine (Fig. 2).