A team of agricultural and environmental scientists has developed a simple biochar based technology that can strip self toxic chemicals from pepper growing soils and restore healthy seed germination. The work offers a promising new tool to help farmers overcome "continuous cropping obstacles" that have long plagued high value capsicum production.
"Pepper farmers often feel forced to choose between meeting market demand and protecting their soil. Our study shows they do not have to make that trade off," said Xueyan Zhang, the study's first author from the Agro Environmental Protection Institute of the Ministry of Agriculture and Rural Affairs in Tianjin, China. "By combining a natural enzyme with an engineered biochar, we created a robust material that removes toxic phenolic acids from soil and helps pepper plants thrive again."
Pepper is one of the world's most important vegetable crops, but limited arable land and strong demand mean many fields are planted with capsicum year after year. Over time, the pepper roots release and accumulate phenolic acids such as ferulic acid, p hydroxybenzoic acid and related compounds that act as self toxins, weakening plants, suppressing growth and in severe cases killing them. These allelochemicals interfere with cell division, hormone balance and root water and nutrient uptake, making continuous cropping a serious barrier to sustainable production.
Existing physical and chemical treatments to remove these compounds can be energy intensive and may cause secondary pollution, while biological approaches based on beneficial microbes are often unstable under real field conditions. This leaves a critical technology gap for farmers who need effective, practical and environmentally friendly ways to clean up allelochemicals in soil.
Turning tobacco stems into an enzyme reactor
To address this challenge, the researchers converted waste tobacco stems into a highly porous biochar and then chemically etched it with potassium carbonate to create a "carbonate modified biochar" with an ultra high surface area and pore volume. They then used glutaraldehyde crosslinking to immobilize horseradish peroxidase an oxidizing enzyme widely used in biosensors and pollution control onto the modified biochar, producing what they call HRP CBC.
This engineered material could load horseradish peroxidase up to 311.46 units per gram, far higher than many previously reported supports, while maintaining high enzyme activity. Microscopy, spectroscopy and surface area measurements confirmed that the biochar's tailored pore structure and oxygen containing functional groups created abundant sites for stable enzyme attachment and helped protect the enzyme under changing pH and temperature.
Fast removal of toxic phenolic acids
In water tests designed to mimic soil solutions, HRP CBC consistently outperformed both free horseradish peroxidase and enzyme loaded on unmodified biochar across a wide range of conditions. At pH 7 and 35 degrees Celsius, 2 units per milliliter of HRP CBC completely removed a 20 milligram per liter solution of ferulic acid within six hours, two hours faster than the other treatments.
The material also degraded a suite of other phenolic acids linked to yield loss in continuous pepper cropping including vanillic, cinnamic, coumaric and p hydroxybenzoic acids achieving at least 50 percent removal within two hours. Total organic carbon measurements and advanced mass spectrometry showed that ferulic acid was broken down into smaller, less toxic organic molecules through a free radical based mechanism involving reactive oxygen species. Toxicity modeling indicated that as the reaction proceeded, the products shifted from moderately or acutely toxic to low or non toxic, supporting the technology's detoxification potential.
Reviving pepper seed germination
To test whether these chemical changes translate into real biological benefits, the team exposed pepper seeds to ferulic acid solutions with and without HRP CBC treatment. Seeds exposed to ferulic acid alone showed a 17 percent drop in germination rate and a 0.79 centimeter reduction in root length compared with water controls.
When the ferulic acid solution was first treated with HRP CBC for six hours, the inhibitory effect disappeared, and both germination and root growth rebounded to levels statistically similar to the control group. In soil spiked with ferulic acid, HRP CBC reduced the toxin concentration by 84.68 percent within 11 days, suggesting strong potential for practical soil remediation.
Toward field ready green remediation
HRP CBC also demonstrated improved stability and reusability, retaining more than half of its activity after 30 days of storage and maintaining substantial degradation capacity over seven reuse cycles. The authors note that the biochar support not only shields the enzyme from harsh environmental conditions but also concentrates pollutants in its pores, increasing contact between enzyme and substrate.
"By upgrading agricultural waste into a smart enzyme carrier, we offer a green and scalable strategy to tackle phenolic self toxicity in continuous cropping systems," said corresponding author Feng Wang. "The next step is to move from laboratory tests to longer term field trials so that farmers can safely apply this technology to real pepper fields."
The study points to a future in which waste biomass, tailored surface chemistry and biocatalysis work together to maintain soil health and protect crop yields under intensive production.
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Journal Reference: Zhang, X., Lv, S., Yuan, T. et al. Efficient allelochemical removal from continuous capsicum cultivation using horseradish peroxidase–loaded biochar. Biochar 8, 2 (2026).
https://doi.org/10.1007/s42773-025-00512-9
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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.
