Effects of wheat straw derived biochar on cadmium availability in a paddy soil and its accumulation in rice

This study was carried out to investigate the effect of biochar amendment on cadmium (Cd) availability in a paddy soil with biochar amendment and its effect on the accumulation in rice. Biochar was applied once at rates of 0 (A0), 10 (A10), 20 (A20), 30 (A30), and 40 (A40) t ha−1 on the soil surface layer (0–17 cm). Results showed that the soil organic matter (SOM) content and pH in 0–17 cm soil layer increased as biochar application rate increased, whereas the content of dissolved organic carbon (DOC), and available iron (Fe), manganese (Mn), aluminum (Al) in diethylenetriamine pentaacetic acid (DTPA) extracts declined with biochar added. Available Cd in DTPA extracts in the 0–17 and 17–29 cm soil layer of A40 treatments was significantly lower (p A10 > A20 > A30 > A40. DTPA extractable Cd concentration in soil was the key factor affecting the Cd uptake by rice roots. In conclusion, biochar application at 40 t ha−1 can effectively reduce the availability of Cd in soil profile, enhance the available Cd enrichment in micro-aggregates, and thus limit the Cd uptake by rice.