A Targeted Approach to Soil Cadmium
Cadmium (Cd) contamination in agricultural soils can threaten the safety of food and medicinal plants because the fraction available in soil is closely linked to plant uptake. Mining, inappropriate fertilizer use and sewage irrigation are among the human activities associated with soil heavy-metal pollution. Biochar can immobilize metal ions through processes including complexation, precipitation and ion exchange, but its effectiveness depends on the biomass used to make it and the production conditions. A tailored approach is therefore important when using biochar to reduce Cd availability.
Authors Xiaochen Zhu , Carol Sze Ki Lin , Ziting Wang , Chong Li , and colleagues from Kunpeng Institute of Modern Agriculture at Foshan , City University of Hong Kong , and Guangxi University , among other institutions, combined a meta-analysis with laboratory and pot experiments. They screened 3,339 articles published between 2001 and 2024 and included 134 studies meeting their criteria, extracting 640 comparisons. The analysis assessed how biochar feedstock, pyrolysis conditions, modification, application rate and soil properties related to available soil Cd and plant Cd accumulation. The team then prepared biochars from four Chinese medicine residues, tested Cd adsorption kinetics, and conducted pot experiments with lettuce, dandelion and Lanzhou lily.
Patterns Across Published Studies
Across the studies included in the meta-analysis, biochar application was associated with a 10.8% increase in soil pH and a 37.9% decrease in available Cd. Soil cation exchange capacity (CEC) and soil organic matter increased by 23.9% and 48.6%, respectively, while plant Cd accumulation decreased by 41.1%. Plant biomass increased by 41.9% in the pooled analysis. The authors note that the changes in soil properties may help immobilize Cd, but the meta-analysis also found significant variation in outcomes across preparation and soil conditions.
Feedstock and production settings were associated with differences in Cd immobilization. Biochars made from medicinal materials classified as Fructus and Semen or Herba reduced available soil Cd by 36.8% and 35.0%, respectively. Across the analyzed studies, biochar produced below 400 °C achieved a 40.4% reduction, while production lasting 3–4 h was associated with a 50.7% reduction. The mixed-effects analysis indicated that temperatures below 500 °C and durations longer than 3 h generally improved immobilization, although the best conditions varied by feedstock. Biochar with oxygen content above 20% or nitrogen content above 1.5% showed the greatest reductions in the subgroup analysis, but the authors did not experimentally validate targeting these elemental contents.
Testing a Herbaceous Biochar
The researchers compared biochars made from residues of Houttuynia cordata , Sargentodoxa cuneata , Siraitia grosvenorii and Paeonia suffruticosa . In adsorption experiments, the biochar made from Houttuynia cordata residue, designated BHC, had a maximum Cd²⁺ adsorption capacity of 29.5 mg g⁻¹. This exceeded the capacities measured for biochars from Paeonia suffruticosa (11.4 mg g⁻¹), Sargentodoxa cuneata (8.2 mg g⁻¹) and Siraitia grosvenorii (1.5 mg g⁻¹). The biochars were tested in solution as a comparative screening step; the authors caution that these kinetic experiments were not intended to reproduce soil conditions.
A biochar made from Houttuynia cordata residue at 450 °C for 3.5 h, called BHC3, was selected for further testing. In acidic, Cd-spiked soil, applying BHC3 at 2% by weight reduced available soil Cd by 17.6% and lettuce Cd accumulation by 52.3% relative to the untreated control. In the same lettuce experiment, biochar from Paeonia suffruticosa reduced available soil Cd by 18.6% and plant Cd accumulation by 54.0%. For BHC3, the adsorption data were better described by a pseudo-second-order kinetic model (R² = 0.997), which the authors interpret as consistent with a chemisorption-dominated process. The experiments used three replicates per treatment.
Cross-Species Results and Next Steps
Further pot experiments assessed BHC3 in two medicinal food plants noted for heavy-metal accumulation. In dandelion ( Taraxacum officinale ), BHC3 reduced available soil Cd by 18.0%–55.5% and plant Cd accumulation by 42.9%–68.6%. In Lanzhou lily ( Lilium davidii var. willmottiae ), the biochar reduced available soil Cd by 18.0%–55.5% and plant Cd accumulation by 42.9%–68.6% across the reported plant experiments. These findings suggest potential for the tested biochar across the three species under the experimental conditions. The results concern pot trials in acidic, Cd-spiked soil, rather than field performance.
The study presents a meta-analysis-guided method for selecting biochar feedstocks and production conditions, and identifies Chinese medicine residues as a potential feedstock for soil remediation. The authors conclude that optimal performance was achieved with herbaceous biochar produced at 401–500 °C for 3–4 h and applied at 2% by weight. They state that further validation across a broader range of soil types and field conditions is necessary. The conclusions therefore indicate promising cross-species potential in acidic Cd-contaminated pot trials, while leaving performance under varied soils and field conditions for future study.
Corresponding Author: Carol Sze Ki Lin or Ziting Wang or Chong Li
Original Source: https://doi.org/10.1007/s44246-026-00302-3
Contributions: Xiaochen Zhu contributed to methodology, data curation, formal analysis, writing – original draft, and visualization. Dai Dai , Beilei Wei , Yanan Yang , Jiawen He , Zhiyan Bai , Haixin Zheng , Weixiong Lin , and Zhenyao Wang contributed to methodology, data curation, and resources. Hailong Wang contributed to writing – review and editing. Carol Sze Ki Lin and Ziting Wang contributed to project administration, writing – review and editing, and validation. Chong Li contributed to project administration, writing – review and editing, supervision, and funding acquisition. All authors read and approved the final manuscript.
Carbon Research
Meta-analysis
Not applicable
Tailored biochar for effective cadmium immobilization in soil and reduced accumulation in plants: a meta-analysis and experimental validation study
8-Sep-2026
Hailong Wang is an Executive Editor-in-Chief of Carbon Research and was not involved in the editorial review of, or the decision to publish, this article. All authors declare that they have no other competing interests.