Cadmium contamination in agricultural soils threatens food safety worldwide, as the toxic metal can accumulate in crops and enter the human food chain. A new study published in the journal Biochar reports that aging silicon-rich biochar derived from rice husks can significantly reduce cadmium uptake in leafy vegetables while improving plant resistance to heavy metal stress.
The research focuses on a special type of biochar known as silicon-rich biochar, or Si-char. Biochar is a carbon-rich material produced by heating biomass such as crop residues under limited oxygen conditions. Scientists have long recognized its potential to immobilize heavy metals in soils. However, once biochar is applied in real environments, it gradually undergoes natural aging processes driven by oxidation, microbial activity, and weathering. Until now, little was known about how these aging processes influence its remediation performance.
In this study, researchers produced Si-chars from rice husk at three different pyrolysis temperatures and then simulated environmental aging using controlled oxidative treatment. They tested the materials in laboratory adsorption experiments and greenhouse pot experiments using pakchoi, a leafy vegetable widely cultivated in Asia.
The results showed that aging dramatically changed the behavior of biochar, and the effect depended strongly on the original pyrolysis temperature. Low-temperature biochar produced at 300 degrees Celsius benefited most from aging. After aging, this material reduced cadmium concentrations in pakchoi leaves by more than 27 percent compared with untreated soil.
According to the research team, the improvement was linked to two key processes triggered during aging. First, aging increased the release of bioavailable silicon and dissolved organic matter from the biochar. These compounds interact with cadmium in soil, lowering its mobility and availability to plants. Second, silicon released from the biochar accumulated in plant tissues, strengthening plant defenses and reducing the transport of cadmium from roots to leaves.
“Our findings show that aging can actually activate certain biochars rather than simply degrading them,” said the study’s corresponding author. “In particular, low-temperature silicon-rich biochars become more effective at immobilizing cadmium after aging because they release beneficial silicon and organic compounds that help protect plants.”
The study also revealed that aged biochar reshaped soil microbial communities. Beneficial bacteria associated with heavy metal immobilization became more abundant in amended soils, contributing to reduced cadmium availability. At the same time, transcriptomic analysis of plant leaves showed that genes related to cadmium transport were suppressed, while antioxidant and stress defense pathways were activated.
Together, these biological responses helped plants tolerate cadmium stress more effectively and limited the accumulation of the toxic metal in edible tissues.
The findings challenge the common assumption that biochar performance inevitably declines over time. Instead, the study demonstrates that aging can enhance the environmental functionality of certain biochars, depending on how they are produced.
“Our work highlights the importance of considering environmental aging when designing biochar-based remediation strategies,” the researchers said. “Understanding how biochar evolves in soil can help optimize its long-term effectiveness for sustainable agriculture.”
By revealing how silicon-rich biochar changes over time and how these changes influence soil, microbes, and plants, the study provides new insights for developing safer and more effective approaches to manage heavy metal contamination in farmland.
The research suggests that properly engineered and aged biochars could become valuable tools for protecting crops and improving soil health in contaminated agricultural systems.
===
Journal Reference: Zhang, Y., Liu, L., Hua, Y. et al. Influence of aged silicon-rich biochars (Si-chars) on leaf Cd accumulation in pakchoi ( Brassica rapa subsp. chinensis ): a pyrolysis temperature-dependent response. Biochar 8 , 37 (2026).
https://doi.org/10.1007/s42773-025-00556-x
About Biochar
Biochar (e-ISSN: 2524-7867) 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 .
Biochar
Experimental study
Influence of aged silicon-rich biochars (Si-chars) on leaf Cd accumulation in pakchoi (Brassica rapa subsp. chinensis): a pyrolysis temperature-dependent response
1-Feb-2026