Effects of biochar amendment on rice Fe/As uptake and growth in mine drainage-polluted paddy soil under continuous...

Paddy fields contaminated by As-containing acid mine drainage exhibit soil acidification and elevated Fe/As levels impairing rice growth. Biochar, featuring unique chemical compositions and physical structures, offers potential for remediating such degraded farmlands. However, biochar ages in soil, necessitating an accurate understanding of its long-term remediation efficacy. In this study, soil contaminated by high-As coal mine drainage was collected and amended with bamboo-derived biochar at application rates of 3 % and 5 % (w/w). A two-year pot experiment was conducted to investigate the geochemical behavioral changes of Fe/As in the soil-biochar-rice system, as well as the impact of biochar aging on rice growth. Results showed that biochar raised the flooded soil pH from 5.5 to 6.2 on average, while increasing soil water Fe/As concentrations by 115.5 % and 24.6 %, respectively. These effects weakened after 1 year of aging. The two dissolved ions were primarily immobilized through complexation with abundant functional groups on biochar surfaces. However, they tended to detach during biochar aging, resulting in a >65 % reduction in immobilization capacity. Over the two-year period, the contents of Fe/As in rice roots decreased due to biochar application, while the As content in rice stems increased. Importantly, the As content in rice grains was not significantly affected. Rice growth experienced minimal stress from the increased soil Fe/As bioavailability. Appropriate biochar application promoted root/stem growth and significantly increased the 1000-grain weight, while excessive application only enhanced root/stem growth, and a certain degree of this growth-promoting effect was maintained even after biochar aging.