New biochar strategy tackles toxic cadmium in rice paddies while locking away carbon

Rice paddies feed billions of people worldwide but face two major challenges: heavy metal contamination and greenhouse gas emissions. Now, researchers have developed a new type of biochar that can address both problems at once—immobilizing toxic cadmium in soil while helping trap carbon, a critical step in slowing climate change.

The study, published in Biochar, tested a phosphorus/iron-doped biochar (PFBC) made from agricultural chestnut shells. By applying this engineered biochar to cadmium-contaminated paddy soils, the team found that it significantly reduced cadmium mobility—limiting the uptake of this harmful metal into rice crops—while simultaneously improving carbon retention in the soil.

“Cadmium contamination threatens food security, and rice is a major exposure pathway for humans,” said corresponding author Xinxin Li of Qingdao University of Science and Technology. “At the same time, paddy fields are hotspots for greenhouse gas emissions. Our findings suggest PFBC can provide a dual benefit: safer rice production and better carbon sequestration.”

Rice paddies are unique because they undergo frequent flooding and drainage cycles, creating fluctuating redox conditions. These cycles often release cadmium back into soil water and accelerate carbon loss. The new study showed that PFBC helped stabilize both cadmium and carbon during these cycles by altering soil chemistry and microbial processes.

Using a combination of soil incubation experiments, microscopic imaging, and DNA sequencing, the researchers found that the biochar:

• Shifted cadmium from its most mobile forms into more stable mineral-bound fractions.

• Reduced the release of carbon dioxide during drainage while maintaining soil organic matter.

• Enhanced beneficial interactions between organic carbon and iron minerals, improving long-term stability.

• Influenced microbial communities in ways that favored cadmium immobilization and carbon retention.

The results point to a “synergistic” role of phosphorus and iron in the biochar. Phosphorus promotes cadmium binding and precipitation, while iron drives redox reactions that help protect organic carbon. Together, they provide multiple pathways for stabilizing contaminants and storing carbon in the soil.

The authors caution that while the laboratory results are promising, long-term field trials are still needed to confirm stability under real-world farming conditions. If successful, PFBC could represent a sustainable approach to managing contaminated soils while contributing to climate mitigation goals.

“This research highlights how agricultural waste can be transformed into a powerful tool for cleaner food production and environmental protection,” said Li. “It opens the door for practical biochar strategies that deliver co-benefits for farmers, ecosystems, and society.”

=== 

Journal Reference: Shi, H., Chen, Y., Xing, Y. et al. Phosphorus/iron-doped biochar enabling a synergy for cadmium immobilization and carbon sequestration in fluctuating redox paddy soils. Biochar 7, 91 (2025). https://doi.org/10.1007/s42773-025-00481-z 

=== 

About Biochar

Biochar is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field. 

Follow us on Facebook, X, and Bluesky.