Effect of Modified Biochar on Cadmium Uptake and Accumulation in Chinese Cabbage

In this study, adsorption of soil cadmium (Cd) by biochar and modified biochar was explored for remediation of Cd pollution in agricultural fields. Seven pot trial treatments were conducted using Chinese cabbage (Brassica campestris) grown without biochar or with biochar prepared from corn stover that was either unmodified or modified with potassium permanganate at 0.4 mol·L^-1. The treatments are without biochar (CK, control), with unmodified biochar applied at 20 (A1 treatment), 50 (A2 treatment), or 100 g·kg^-1(A3 treatment), or with modified biochar applied at 20 (A4 treatment), 50 (A5 treatment), and 100 g·kg^-1(A6 treatment). The different treatments were investigated for their Cd adsorption capacities and their effects on the pH, organic matter content, and content of available Cd of the soil, and the content, enrichment coefficient, and transport coefficient of Cd in the edible part and roots of the plant. The modified biochar treated with potassium permanganate solution at a concentration of 0.4 mol·L^-1 showed the strongest adsorption capacity for cadmium, with an adsorption amount of 7.46 mg·g^-1. Both biochar and modified biochar greatly increased the pH and organic matter content of the soil, and the A3 and A6 treatments (application at 100 g·kg^-1) resulted in the largest changes. Furthermore, both biochar and modified biochar greatly reduced the available Cd in the soil, and the reduction effect was better with modified biochar than biochar at the same application rate. The Cd content, enrichment coefficient, and transport coefficient in the edible part of Chinese cabbage greatly decreased with both biochar and modified biochar, and A5 treatment had the greatest effect. Compared with the control treatment, A5 treatment decreased the Cd content, enrichment coefficient, and transport coefficient by 90.83%, 88.89%, and 86.82%, respectively. Compared with the control treatment, A6 treatment resulted in 30.77% less Cd enrichment in the Chinese cabbage root-the largest reduction among all the treatments. These results show that application of biochar and modified biochar can effectively remediate Cd contamination in soil planted with Chinese cabbage and block transfer of Cd into the plant and its subsequent enrichment. The effects of modified biochar are better than those of unmodified biochar. Biochar production uses agricultural waste and its application provides a way to safely produce vegetables in soil with heavy metal pollution.