Effects of Biochar on Cadmium Accumulation in Rice and Cadmium Fractions of Soil: A Three-Year Pot Experiment

A three-year rice pot experiment was conducted to investigate the effects of biochar on cadmium (Cd) accumulation in rice and Cd fractions of soil. The biochar was derived from farmland waste and applied to contaminated paddy soil at various application rates (0, 1, 2, and 4%). The dry matter accumulations in rice, Cd contents of various rice organs, and fraction distributions of Cd in soil were measured. In a 3-year experiment, the results indicated that biochar treatments reduced the exchangeable Cd concentrations by 28.5 to 59.4% in soil, the total Cd accumulations in rice by 2.7 to 23.8%, and promoted rice growth by 0.7 to 3.9%. The application rates of 2% to 4% were considered to be reasonable for both rice growth and remediation of Cd-contaminated soil. Meanwhile, the Cd-contaminated biochar and straw were studied in the above manner for two years. Contaminated biochar reduced the Cd content of individual rice plants and ensured the normal growth of rice, but it had little effect on the Cd contents in specific organs of rice and Cd fractions of soil. However, this indicated that contaminated biomass materials have the possibility to be reused after pyrolysis for remediation of contaminated paddy soil.