Organic fertilizer helps biochar immobilize cadmium in contaminated soil

Cadmium contamination in farmland is a persistent threat to crop safety because the metal can be taken up by plant roots and travel into the food chain. A new experimental study reports a strategy to curb cadmium mobility in soil by pairing biochar with carefully fractionated dissolved organic matter (DOM) derived from commercial organic fertilizer.

Researchers produced pomelo-branch biochar and loaded it with DOM separated into three molecular-weight ranges: low (<3 kDa), medium (3–10 kDa), and high (>10 kDa). The team then evaluated how each composite influenced cadmium adsorption, soil chemical behavior, and cadmium uptake by Chinese cabbage, using controlled laboratory and pot experiments.

Adsorption tests showed that loading DOM onto biochar boosted cadmium capture compared with biochar alone. Performance generally increased with DOM molecular weight, suggesting that larger organic molecules provide more effective binding environments. The best-performing composite achieved a maximum adsorption capacity of 84.25 mg/g, versus 54.53 mg/g for unmodified biochar.

To understand why, chemical analyses linked immobilization mechanisms to molecular characteristics. High-molecular-weight DOM appeared to promote cadmium interactions with aromatic π-electrons, strengthening surface association. Lower-molecular-weight fractions, in contrast, contributed more through oxygen-containing functional groups that can complex with cadmium ions.

When applied to cadmium-contaminated agricultural soil, the composites measurably altered soil chemistry over a 90-day incubation. Soil pH increased by 0.43 to 0.84 units, while available cadmium dropped by roughly 71% to 74% by the end of the experiment.

The amendments also shifted cadmium into less mobile chemical forms. Water-soluble, easily transported cadmium decreased, while the residual fraction rose by up to 123.77%, a change associated with reduced accessibility to organisms.

In pot trials, all biochar–DOM composites reduced cadmium accumulation in the edible shoots of Chinese cabbage, with the strongest treatments lowering shoot cadmium concentrations by as much as 74.46%. Larger-DOM composites also more effectively limited plant enrichment and reduced root-to-shoot transfer.

Although the highest-molecular-weight treatments produced the largest cadmium reductions, they sometimes suppressed cabbage biomass under certain conditions, emphasizing the need to optimize application rates to balance remediation benefits with crop productivity.

Overall, the study provides a molecular blueprint for designing “precision” soil amendments from agricultural residues and fertilizer components—by tuning DOM fraction size to steer cadmium toward stable, less bioavailable forms.

News Publication Date: 6-May-2026

Web References: https://doi.org/10.48130/aee-0026-0008

References: Wei L, Liu D, Chen W, Huang L, Jiang S, et al. 2026. Enhancement of organic fertilizer-derived dissolved organic matter fractions on cadmium immobilization by biochar composites in contaminated soil. Agricultural Ecology and Environment 2: e013. doi:10.48130/aee-0026-0008