Effect of acidified biochar on bioaccumulation of cadmium (Cd) and rice growth in contaminated soil

Abstract The contamination of cadmium (Cd) in the agricultural lands due to the irrigation of untreated wastewater and raw city effluents has become a serious issue with further increment being done by other anthropogenic activities. This practice has become a serious health hazard for humans as cereal crops like rice (Oryza sativa L.) can accumulate significant Cd and become unsafe to consume. Application of organic amendments like biochar has significant reported effects on Cd immobilization and mitigation of Cd toxicity in plants. Modifications in biochar have become well-practiced to enhance its efficacy, especially in alkaline soils. The objective of our study was to test the Cd stress mitigation in rice mediated by the acid-treated biochar. Acid Treated rice husk biochar (RHB) was prepared by treating RHB with three acids (HCl, HNO3, H 3 PO4), each applied at 2 levels (2.5 N and 5 N). Acid-treated biochars were applied at 2% making a total of 8 treatments including 2 controls (contaminated/spiked and non-contaminated). Rice growth, paddy yield, and Cd accumulation proved the efficacy of 5 N H 3 PO 4 treatment of RHB as the most efficient treatment. Compared to contaminated control, 5 N H 3 PO4-RHB application has shown the most significant increment in rice growth (plant height 48.8%, spike length 36.4%, root length 58.8%, root dry weight 234%, straw yield 132.9%, paddy yield 61.7% increase compared to contaminated control). The 5 N H 3 PO4-RHB also decreased bioavailable Cd in soil by 87%, and its accumulation in shoot and paddy by 83.4% and 95.7%, respectively compared to contaminated control. The HCl treatment has shown some toxicity, which might be due to excess of chloride.