Effectiveness of Passivator Amendments and Optimized Fertilization for Ensuring the Food Safety of Rice and Wheat from Cadmium-Contaminated Farmland

The effect of various soil amendments on cadmium (Cd)-contaminated farmland was evaluated in terms of effectiveness, safety, economics, and simplicity. Experiments were conducted in May 2020, on Cd-contaminated land in Tong Ling, An Hui, China. The efficacy of optimized fertilization and heavy metal passivators—gypsum, bamboo charcoal, lime, and a compound passivator (mixture of bamboo charcoal, silicon fertilizer, gypsum, furfural residue, plant ash, and chicken manure)—was evaluated as amendments to reduce the uptake of Cd in rice. The results indicate that all treatments reduced the Cd bioavailability in Cd-contaminated soil and rice grain Cd accumulation to levels that meet national food safety standards. Moreover, the rice yield increased by 4.80 to 14.27% and the Cd content in rice grains decreased by 23.53 to 36.83%. The efficacy of Cd reduction in rice was as follows: optimized fertilization > lime > compound passivator > bamboo charcoal > gypsum powder. Wheat was planted after the rice season to test the effect of the soil amendment measures implemented during the rice season on crop growth in the next season. Wheat yield improved by 3.46 to 10.96%, and the grain Cd content decreased by 6.47 to 41.03%. The efficacy of Cd reduction in wheat was as follows: lime > compound passivator > optimized fertilization > gypsum powder > bamboo charcoal. Following the lime treatment, the wheat grain Cd content met national food safety standards. A comprehensive comparison was conducted to evaluate the safe utilization and economic effect of the passivator and optimized fertilization. The results reveal that optimized fertilization was the most effective treatment. The findings from this study provide a scientific basis for safe rice–wheat rotation systems on mildly Cd-contained farmland (0.3 mg/kg < Cd < 1.0 mg/kg) in the Yangtze River Basin