Immobilization of exchangeable Cd in soil using mixed amendment and its effect on soil microbial communities under paddy upland rotation system

Cadmium (Cd) pollution is a widespread environmental problem that decreases crop production, destroys the microbial ecology of soil, and poses a severe risk to human health. Organo-chemical amendment is a cost-effective, eco-friendly, and community-acceptable widely applied an in situ technique for metal-contaminated farmland. In this study, we mixed lime, zeolite, calcium magnesium phosphate fertilizer, and biochar in a mixture ratio of 71:23:5:1 to form a mixed amendment. Field and laboratory experiments were conducted to study the effects of the mixed amendment on soil exchangeable Cd content, plant Cd accumulation, and soil microbial community. It was found that the application of 0.5% mixed amendment decreased exchangeable soil Cd by more than 85% and 64% in wheat and rice season, respectively, compared with control (CK), without increasing pH. Moreover, the application of 0.5% mixed amendment decreased Cd accumulation in grains by 22.9% and 41.2% in wheat and rice season, respectively, compared to CK. The result of phospholipid fatty acids (PLFAs) shows that the level of soil microbial diversity and species richness under mixed amendment treatments were higher than in lime treatment, indicating more copiotrophic conditions and faster rate of nutrient turnover in mixed amendment than pure lime treatment. Hence, it concluded that the mixed amendment has a strong effect on fixing exchangeable soil Cd and reducing the accumulation of Cd in crops. Finally, it was observed that the mixed amendment improved the soil microbial community structure and accelerate the rate of nutrient turnover by microbes under this favorable condition comparative to individual treatments.