Effects of magnetic hydroxyapatite loaded biochar on Cd removal and passivation in paddy soil and its accumulation in rice: a 2-year field study

Stabilized cadmium (Cd) was extremely easy to be re-released into the environment. The study was aim to explore the Cd removal efficiency and passivation in paddy soil by magnetic hydroxyapatite loaded biochar (MHBC), and to investigate the effect of MHBC on Cd accumulation and yield of rice with low Cd accumulation cultivar named ZhuLiangYou189 (ZLY189) and conventional cultivar named ZhuLiangYou929 (ZLY929) in 2-year field trials. These results shown that MHBC under the high dosage of 25.2 t/ha can effectively decrease the bioavailable Cd (from 0.4 to 0.24 mg/kg) and total Cd (from 1.42 to 0.86 mg/kg). For ZLY929, only with the dosage of 25.2 t/ha MHBC, the grain Cd content can meet the contaminant limits in grain (≤ 0.2 mg/kg) during 2 years. While for ZLY189, the grain Cd content in 6.3 t/ha, 12.5 t/ha, and 25.2 t/ha decreased to 0.13 ~ 0.17 mg/kg, to 0.07 ~ 0.10 mg/kg, and to 0.05 ~ 0.08 mg/kg during 2 years, respectively. What's more, the application of MHBC has no environmental risk and increase grain yield by boosting soil nutrient substance. Thus, the application of MHBC was a promising remediation technology in Cd-contaminated paddy soil.