Response of plant and soil microbes to biochar amendment of an arsenic-contaminated soil

Abstract The historical treatment of livestock with arsenical-based pesticides has resulted in large areas of pastoral land being highly contaminated with arsenic. This study investigated the effect of biochar on soil microbial activity and arsenic phytoextraction in an arsenic-contaminated soil during a 180 d glasshouse experiment. Biochar made from willow feedstock ( Salix sp ) was pyrolysed at 350 and 550 °C (representing a low- and high-temperature biochar) and amended to soil at rates of 30 t ha −1 and 60 t ha −1 to 30 cm depth (10 and 20 g biochar kg −1 soil, respectively). Ryegrass ( Lolium perenne L.) was seeded and plant growth was monitored. Soil microbial activity, quantified using the dehydrogenase activity (DHA) assay, was significantly increased ( P P −1 to 60 t ha −1 shoot tissue of ryegrass extracted significantly higher ( P −1 compared to ryegrass grown on unamended soils. This would correspond to an increase in the extraction of total arsenic by 14,000 mg ha −1 compared to unamended soils and in doing so decreasing soil remediation times by over 50%. This investigation provides insight into the beneficial attributes of biochar in contaminated soil, and specifically that produced from willow wood, and its potential to reduce the time needed to remediate arsenic-contaminated soil. However, more studies are needed to understand the mechanisms through which these benefits are provided.