Sunflower Bottom Ash Improve Soil Properties and Microbial Community in Cadmium-Polluted Acid Farmland

Sunflower bottom ash (SBA), rich in potassium (K) and low in heavy metals, making it a potential solution for cadmium (Cd)-polluted acidic farmland. Field experiments were conducted to investigate the effects of adding different concentrations of SBA (0%, 0.1%, 0.3%, 0.5%, 1.0%) to Cd-contaminated acidic soil on heavy metal bioavailability, soil fertility, and bacterial community structure. The results showed that the bioavailability of Cd decreased from 0.29 mg/kg in the CK treatment to 0.08 mg/kg in the 1% treatment, and the pH increased from 5.7 to 8.1. Notably, in the 0.3% treatment, catalase, urease, and alkaline phosphatase activities reaching 20, 560, and 4.3 (a.u), respectively, and 16S rRNA sequencing analysis revealed that the Shannon index of the 0.3% treatment was the highest at 5.364, indicating the most favorable soil environment with the greatest microbial diversity. Terrabacter was significantly positively correlated with heavy metal availability, while Dyella exhibited significant positive correlations with the availability of phosphorus (P), K, and soil pH, and Terrabacter and Dyella in the acidic Cd-contaminated soil contributed to reducing heavy metal toxicity and enhancing soil fertility. This study offers a promising approach for resource utilization of SBA, and provides a new technology for improving Cd-polluted acidic farmland.