Combined application of biochar and nano-zeolite enhanced cadmium immobilization and promote the growth of Pak Choi in cadmium contaminated soil

Biochar and zeolite have been demonstrated effective to remove heavy metals in soil; however, the effect of combined application of the both materials on the fraction of Cd and soil-plant system are largely unknown. Cd fractions in soil, growth and Cd uptake of Pak Choi were measured after the combined application of biochar (0, 5, 10 and 20 g·kg-1) and nano-zeolite (0, 5, 10, 20 g·kg-1) by pot experiment. Results showed that both single and combined application reduced the exchangeable Cd in soil and improved the plant growth. However, combined application of 20 g·kg-1 biochar with 10 g·kg-1 nano-zeolite showed the strongest effect, with the residual Cd in soil increased by 214% as compared with control. 20 g·kg-1 biochar with 10 g·kg-1 nano-zeolite Mechanic studies showed that this combination enhanced the antioxidant system, with the SOD, CAT and POD activities enhanced by 56.1%, 133.3% and 235.3%, respectively. The oxidative stress was reduced correspondingly, as shown by the reduced MDA contents (by 46.7%). This combination also showed the best efficiency in regulating soil pH, organic matter and soil enzymes thus improving the plant growth. This study suggests that combined application various materials such as biochar and nano-zeolite may provide new strategies for reducing the bioavailability of Cd in soil and thus the accumulation in edible plants.